Experimental Physics Division

The LEP Programme

ALEPH

In 2003 the ALEPH Collaboration (Aachen, Annecy, Barcelona, Bari, Beijing, CERN, Clermont-Ferrand, Copenhagen, Demokritos, Ecole Polytechnique, Firenze, Frascati, Glasgow, Haverford College, Heidelberg, Imperial College, Innsbruck, Lancaster, Louvain-la-Neuve, Mainz, Marseille, Milano, MPI München, Orsay, Pisa, RAL, Royal Holloway, Saclay, Santa Cruz, Shefﬁeld, Siegen, Trieste, Washington, Wisconsin, Zurich) completed and published several ﬁnal physics analyses. The data collected during the life of the experiment and the software developed over many years have been archived to allow long-term analysis of ALEPH data.

The ﬁnal results on the search for the lightest supersymmetric particle (LSP), one of the main candidates for explaining the existence of the dark matter in the universe, have been complemented by a thorough search for stable hadronizing squarks and gluinos. The analysis of event-shape variables and inclusive particle spectra at the highest LEP energies was completed and the energy evolution of the strong coupling constant was studied in detail. The cross-section of the process e+e– → W+W– was measured with high precision. Many interesting results in two-photon physics were published.

Overall, 15 papers were published or submitted for publication by ALEPH during 2003.

Searches

Charginos and Neutralinos were searched for in the data collected at centre-of-mass energies up to 209 GeV. In the many topologies considered, the number of candidates observed was consistent with the background expected from Standard Model processes. An absolute lower limit of 43.1 GeV/c2 was derived on the mass of the LSP, assumed to be the lightest neutralino, in the framework of MSSM and R-parity conservation. The effect of stau mixing was studied in great detail. It was shown that stau mixing would only slightly degrade the above limit. The ﬁnal 95% CL limit on the LSP mass, as a function of tanβ, is shown in Fig. ALEPH–1.

Another important achievement in the search for supersymmetry is the completion of the search for stable hadronizing squarks and gluinos. The ﬁnal publication presents several searches at the Z pole and higher energies. The existence of LSP gluinos is excluded for masses below 26.9 GeV/c2, ﬁnally closing the long-standing low mass gluino window. Down-type (up-type) LSP squarks are excluded for masses below 92 (95) GeV/c2. Stop decaying to gluinos are excluded up to masses of 80 GeV/c2.

Experimental Physics Division 5

Fig. ALEPH–1: The 95% CL lower limit on the mass of the lightest neutralino, as a function of tanβ. The dashed curve indicates the limit from chargino searches 2 β alone for m0 = 500 GeV/c . The grey area at small tan shows the improvement obtained if chargino and neutralino searches are combined. The other limits are obtained from (right to left) slepton searches in the corridor, Higgs boson searches in the corridor, chargino searches for large sfermion masses and Higgs boson searches.

QCD and the Strong Interaction Coupling

Improved tests of QCD have been completed using hadronic ﬁnal-state observables with data collected at LEP1 and LEP2. The measurements include event shape variables, jet rates, and inclusive charged-particle distributions. Particular attention has been given to the study of the energy evolution of these variables. A large α part of the long paper dedicated to this subject discusses the measurement of s from event shape variables. α Non-perturbative aspects of the determination of s are studied by means of power law techniques, which are α corrections scaling with Q, the four-momentum transfer. The ﬁnal result is s = 0.1214 ± 0.0048. The energy evolution of the coupling constant is shown in Fig. ALEPH–2.

Inclusive and Two-Photon Physics

In the area of inclusive physics the publication of a detailed investigation of Bose–Einstein correlations in hadronic Z decays is worth mentioning. The two-pion correlation function is measured in both one and two dimensions, using either unlike-sign or mixed-events reference samples. The results indicate that the correlation radii values depend on the chosen kind of reference sample and on the two-jet purity.

6 Experimental Physics Division

α Fig. ALEPH–2: The measurements of the strong coupling constant s between 91.2 and 206 GeV. The results using six different event-shape variables are combined and correlations are taken into account. The inner error bars exclude the perturbative uncertainty, which is expected to be highly correlated between the measurements. The outer error bars indicate the total error. A ﬁt to the three- loop QCD evolution formula using the uncorrelated errors is shown.

The year 2003 saw the publication of several results on two-photon physics. Charm production in γγ ∗ ∗ collisions has been measured by selecting events containing D + mesons. The differential D + production has been determined as a function of pseudorapidity and transverse momentum and found to be in agreement with NLO QCD calculations. The exclusive production of pion and kaon meson pairs in two-photon collisions has also been investigated and compared to predictions. The angular distributions of these simple exclusive processes are described by QCD, but the data are found to have a signiﬁcantly higher normalization. Another important measurement is related to the hadronic structure of the photon, which has been studied in two regions of momentum transfer (〈Q2〉 = 17.3 GeV2, 〈Q2〉 = 63.2 GeV2) using γγ collisions where one of the scattered electrons is detected.

Electroweak Physics

A precise determination of the W+W– production cross-section, using all of the data collected by ALEPH at LEP2, is ready for publication. Individual cross-sections for the different topologies arising from W decays into leptons and hadrons, as well as the total W-pair cross-section, are measured at ten centre-of-mass energies. The results are found to be in agreement at the one per cent level with recently developed Standard Model calculations. The branching fraction of the W boson into hadrons is measured to be + → BR(W hadrons) = 67.13 ± 0.38 ± 013%, from which the CKM matrix element |Vcs| is determined to be

Experimental Physics Division 7

0.958 ± 0.017 ± 0.007. The W+W– cross-section as a function of the centre-of-mass energy is shown in Fig. ALEPH–3.

The study of anomalous gauge boson couplings is close to completion. Constraints on the existence of anomalous quartic gauge couplings have been obtained from acoplanar photon pairs, and the results are ready for publication. Finally the long, thorough studies related to the measurement of the W mass are essentially completed, and the ﬁnal publication is in preparation.

Fig. ALEPH–3: Measurement of the W-pair production cross-section as a function of the centre-of-mass energy, compared to Standard Model predictions.

DELPHI

The DELPHI Collaboration consists of teams from Ames, Amsterdam, Antwerp, Athens, Bergen, Bologna, Bratislava, Brussels, CERN, Cracow, Dubna, Genoa, Grenoble, Helsinki, Karlsruhe, Lisbon, Liverpool, Ljubljana, Lund, Lyon, Marseille, Milan, Mons, Orsay, Oslo, Oxford, Padua, Paris, Prague, Rio de Janeiro, Rome, Rutherford, Saclay, Santander, Serpukhov, Stockholm, Strasbourg, Torino, Trieste, Udine, Uppsala, Valencia, Vienna, Warsaw and Wuppertal.

The barrel part of the DELPHI detector is being prepared as a permanent exhibit for CERN visitors. It has been moved to its ﬁnal position in pit 8, compatible with the spatial arrangement of the LHCb counting houses. A visitor platform has been installed. Several subdetectors are being prepared to allow viewing of internal construction details. It is foreseen to make the detector exhibit available to the public from summer 2004 onwards.

During 2003 the DELPHI Collaboration continued the analysis of data collected both at the Z peak (LEP1) and at centre-of-mass energies 161–209 GeV (LEP2). Many analyses were ﬁnalized. A total of 15 papers were published or accepted for publication in refereed journals in 2003 and an additional 12 papers were submitted for publication. Out of these, nine papers are based on LEP1 data and covered mainly B and τ physics topics.

8 Experimental Physics Division

A further 16 papers are in preparation and it is expected that ongoing analyses will lead to another 25 papers in 2004–2005.

A total of 47 contributions were submitted to the 2003 Europhysics Conference on High-Energy Physics in Aachen and the Lepton–Photon Symposium at Fermilab. DELPHI and other LEP results were presented by some 45 DELPHI members at conferences during 2003.

Heavy Flavour and τ Physics

Using high-performance neural network techniques, precise measurements of B+, B0 and mean b-hadron τ τ lifetimes have been obtained: B+ = 1.624 ± 0.014(stat) ± 0.018(syst) ps, B0 = 1.531 ± 0.021(stat) ± τ + 0.031(syst) ps and b = 1.570 ± 0.005(stat) ± 0.008(syst) ps. The B and average b-hadron lifetime are the most accurate to date.

The measurement of the fraction of B+ mesons in a sample of weakly decaying b-hadrons from Zbb→ decays is so far the most precise one: f =±()40.99 0.82(stat) ± 1.11(syst) % . Bu

0 → ∗+l − ν The CKM matrix element |Vcb| has been measured from the decays BDd l using exclusively ∗ reconstructed D + decays. Combining this measurement with a more inclusive measurement, previously published by DELPHI, results in |Vcb| = 0.0414 ± 0.0012(stat) ± 0.0021(syst) ± 0.0018(theor).

In the τ sector, the final results on the τ lifetime and on the exclusive and semi-exclusive hadronic branching ratios of final states with up to five (resp. six) hadrons have been submitted for publication. The results are in good agreement with current world averages and have slightly smaller or similar errors compared to measurements from other experiments. Tau-pair production has also been studied in photon–photon collisions at LEP2 energies. The measurement of the production cross-sections has been used to establish limits on the anomalous magnetic moment and electric dipole moment of the τ lepton. The results are –0.052 –16 < aτ < 0.013 and |dτ| < 3.7 × 10 e⋅cm respectively.

QCD

The measurement of ﬁve event-shape distributions and their mean values at CMS energies from 183 to α 207 GeV have been compared to QCD predictions. From the mean values the strong coupling constant s was α determined using four different methods and the running of s with energy was veriﬁed. An example of a result is shown in Fig. DELPHI–1. Combining the new results with those obtained at lower LEP2 energies and α β at those obtained around the Z peak gives s(MZ) = 0.1157 ± 0.0033. The QCD function is described by

− dα 1 s = 1.11 ± 0.09(stat) ± 0.19(syst), dslog to be compared with the QCD expectation of 1.27.

Experimental Physics Division 9 s α 0.15 αs from means with power corrections 0.14 1/logE fit

0.13 QCD evolution

0.12

0.11

0.1

50 100 150 200 √s (GeV) α Fig. DELPHI–1: Energy dependence of s as obtained from event-shape variables. The total and statistical (inner error bars) uncertainties are shown. The band displays the average values of these measurements when extrapolated according to the QCD prediction. The dashed lines show the result of the 1logs ﬁt.

Searches

After the completion of the search for the SM and MSSM neutral Higgs bosons last year, several other searches for new particles were ﬁnalized during 2003. No evidence for the production of these particles was found and mass limits could be set. The lower mass limit for a Higgs boson produced according to the SM, but which decays invisibly was set at 112.1 GeV/c2. The lower mass limits for the charged Higgs boson in a type- II Two Higgs Doublet Model (2HDM) are shown in Fig. DELPHI–2 as a function of the branching ratio into 2 2 τντ. A charged Higgs boson with a mass lower than 74.4 GeV/c (type-II 2HDM) or lower than 76.7 GeV/c (type-I 2HDM) is excluded at 95% CL.

Higgs boson production with the Higgs decaying into photons was also searched for. In a model where the Higgs couplings to bosons have SM values, but the couplings to fermions vanish (fermiophobic Higgs), a lower limit on the mass of the h0 could be set at 104.1 GeV/c2. Exclusion limits were also derived in the mass plane ()MM, of the fermiophobic 2HDM scenario. hA00

The measured single- and multiphoton cross-sections are in agreement with expectations from the SM for + – the process e e → ννγ(γ) and were used to determine the number of light neutrino generations: Nν = 2.84 ± 0.10(stat) ± 0.14(syst). Several model-independent limits on the production of new neutral states have been determined. In particular, new limits were set on the gravitational mass scale connected to the number of extra dimensions of space in which only gravity can propagate (see Fig. DELPHI–3).

10 Experimental Physics Division ) 1

0.9 → τν

0.8 Br(H

0.7

0.6

0.5

0.4

0.3

0.2 observed limit expected median 0.1

0 40 50 60 70 80 90 2 MH (GeV/c ) Fig. DELPHI–2: The observed and expected exclusion regions at 95% – → τ–ν conﬁdence level in the plane of BR(H τ) vs. MH. These limits were + – – obtained from a combination of search results in the τ νττ ντ, csτ ντ and cscs channels at s = 189–209 GeV, under the assumption that the W∗A decay is forbidden. The non-excluded region around BR = 0.35 becomes excluded at 92% CL.

+ – → γ 104 e e G HPC+FEMC acceptance √s = 180-209 GeV

103

95% C.L. 102 Limit

2 MD = 1.31 TeV/c

Cross-section at 208 GeV (fb) MD = 10 0.82 TeV/c2

2 MD = 0.58 TeV/c

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2 MD (TeV/c ) Fig. DELPHI–3: The cross-section limit at 95% C.L. for e+e– → γG production at s = 208 GeV and the expected cross-section for 2, 4 and 6 extra dimensions.

Experimental Physics Division 11 Standard Model Electroweak Results

In 2003 several ﬁnal results on four-fermion production processes were published. The WW production cross-section as a function of the centre-of-mass energy is shown in Fig. DELPHI–4(a). These measurements alone are a tremendous conﬁrmation of the SM prediction, where large cancellations of the three tree-level Feynman diagrams occur. The measured cross-sections, when compared to the latest theoretical calculations that include full O(α) corrections to the three tree-level processes, and combined over all energies, give a ratio exp./theory = 1.001 ± 0.015.

Also the branching ratio for the leptonic decay of the W boson has been measured and its value, averaged over the three lepton species, is Br(W → ν) = (10.85 ± 0.14(stat) ± 0.08(syst))%, in good agreement with the SM expectation of 10.83%. From this measurement the value of the CKM matrix element |Vcs| can be derived: |Vcs| = 0.973 ± 0.019 ± 0.012. Further analysis of the production and decay angular distributions of the W boson show no evidence for the presence of anomalous couplings between the gauge bosons.

Another channel studied is e+e– → W+W–γ, which involves the coupling of four gauge bosons. The expected cross-section from the SM at LEP2 energies is small. The measured cross-sections are in agreement with the SM expectation [see Fig. DELPHI–4(b)] and are used to establish limits on anomalous couplings γγ γ –2 Λ2 –2 among the four gauge bosons WW and WW Z, e.g. –0.063 GeV < ac/ < +0.032 GeV .

Final papers on the measurements of the W mass, TGCs, single boson (Z, W) and Zγ∗ production are in preparation.

20 (a)700 ± % (b)

(fb) SM 5

γ 17.5 2 –2

YFSWW and RacoonWW WW Λ 600 ac/ (GeV ) σ +0.06 15 500 +0.02 12.5 –0.06 –0.02 18 400 10

WW Cross Section (pb) 17.5 300 7.5 17 16.5 200 5 16 100 2.5 15.5

187.5 190 192.5 195 197.5 200 202.5 205 207.5 0 0 160 170 180 190 200 210 180 185 190 195 200 205 210 √s (GeV) √s (GeV) Fig. DELPHI–4: Left: Measurements of the WW cross-section compared with the Standard Model prediction given by the YFSWW and RacoonWW programs. The shaded band represents the uncertainty on the theoretical calculations. Right: W+W–γ cross-section as a function of the centre-of-mass energy. The measured cross-sections (crosses) are compared to the SM prediction from WPHACT/ YFSWW. The cross-sections obtained with EEWWG for indicative values of the Λ2 –2 anomalous parameter ac/ (in GeV ) are also shown.

12 Experimental Physics Division L3

L3 is a collaboration of institutes from Aachen (RWTH), Amsterdam (NIKHEF and Amsterdam), Ann Arbor (Michigan), Annecy (LAPP), Basel, Baton Rouge (Louisiana State), Beijing (IHEP), Bologna (INFN), Boston (Northeastern), Bucharest, Budapest, Cambridge (MIT), CERN, Chandigarh (Panjab), Debrecen, Dublin, Florence (INFN), Geneva, Hamburg, Hefei, Lausanne, Los Alamos, Lyon (IPN), Madrid (CIEMAT), Melbourne (Florida Tech.), Milano (INFN), Moscow (ITEP), Mumbai (Tata), Naples (INFN), Nicosia (Cyprus), Nijmegen, Pasadena (Caltech), Perugia (INFN), Pittsburgh (Carnegie Mellon), Princeton, Riverside (UCR), Rome (INFN), St Petersburg (NPI), Salerno (INFN), San Diego (UCSD), Soﬁa, Taegu, Taiwan, Villigen (PSI), West Lafayette (Purdue), World Laboratory, Zeuthen (DESY) and Zürich (ETH).

The L3 experiment was designed as a general-purpose detector with emphasis on the measurement with good spatial and energy resolution of electrons, photons, muons and jets produced in e+e– interactions at LEP. During the year 2003, the L3 Collaboration continued the analysis of the data collected at centre-of-mass energies around and above the Z pole up to s = 209 GeV. Many analyses were ﬁnalized and their results published, while some more studies continued and are now approaching completion.

In 2003, the L3 Collaboration submitted 18 papers to Physics Letters B and contributed 50 papers to the 2003 Europhysics Conference on High Energy Physics, EPS 2003, held in Aachen (Germany). Members of the collaboration were often invited to give presentations of L3 results or for LEP-wide reviews. More than 20 talks were given by L3 members at conferences and workshops.

By fully exploiting the L3 performance for photon detection, a precision study of events with photons and missing energy was completed, with the results presented in Fig. L3–1. These data, published in a form which allows future interpretations, improve the direct measurement of the number of light neutrino families to Nν = 2.98 ± 0.05 ± 0.04. Dedicated triggers allow measurements of photons with very low energy which yield stringent limits on possible manifestations of supersymmetry and Extra Dimensions.

Direct searches for scalar leptons and scalar quarks were completed, and resulted in severe constraints on the mass of these particles. No evidence was found for pair- and single-production of charged and neutral excited leptons in a comprehensive study which gave mass limits for any possible coupling of excited leptons. In 2003, L3 completed its search for Higgs bosons produced in models beyond the Standard Model. No evidence was found for charged or doubly-charged Higgs bosons. According to the Higgs branching ratio, 95% conﬁdence level (CL) mass limits were established between 76.5 GeV and 82.7 GeV for charged Higgs bosons and between 95.5 GeV and 100.2 GeV for doubly-charged Higgs bosons. In addition, a ﬂavour- independent search was performed for neutral Higgs. The current hypothesis that neutral Higgs bosons mainly decay into b quarks was relaxed and no candidate events were observed in excess of the background expectations. For a Higgs production mechanism analogous to that of the Standard Model Higgs boson, a lower limit of 110.3 GeV (95% CL) was derived for the mass of the Higgs boson.

One of the main objectives of the high-energy programme at LEP is the study of properties of the W boson. The L3 Collaboration measured the triple-gauge-boson couplings of W bosons to be in agreement with the Standard Model expectations, hence confirming the cornerstone prediction of the existence of self-couplings among gauge bosons. In a complementary study, significant spin correlations between the W bosons produced in the e+e– → W+W– process were observed for the first time. While the measurement of the cross-section for

Experimental Physics Division 13 W pair-production at LEP is nearing completion, several dedicated studies, aimed to control the systematics in the complex measurement of the mass of the W boson, were ﬁnalized. First, the reconstruction methods were validated by measuring the mass of the Z bosons produced in association with a photon, in a study which also gave information on the LEP beam energy. Another potential source of systematic uncertainty in the determination of the W mass is the ‘cross talk’ between hadrons stemming from different W bosons. A dedicated study of the particle ﬂow in W pair-production events found that extreme models for this phenomenon are disfavoured. A novel investigation of three-jet events at the Z pole supplied additional information on many models for colour reconnection.

(a) Data Data (b) 300 _ _ ννγ(γ) ννγγ(γ) 20

200

10 Events / 4 GeV 100 Events / 4 GeV

0 0 0 50 100 150 200 0 50 100 150 200 Recoil Mass (GeV) Recoil Mass (GeV)

30 (c) Data_ Data_ (d) 300 ννγ(γ) ννγγ(γ)

20 200

10 100 Events / 0.04 Events / 2 GeV

0 0 0 0.25 0.5 0.75 1 02040 |cosθγ| Eγ2 (GeV) Fig. L3–1: Distributions of a) the recoil mass and c) the polar angle for single- photon events with large missing transverse momentum and of b) the recoil mass and d) the energy of the second most energetic photon for events with two photons and large missing transverse momentum. The pronounced mass peaks are due to the resonant production of a Z boson decaying into neutrinos and the remaining events come from neutrino pair-production mediated by a W boson.

Other measurements were also performed. The branching fraction of hadronic decays of the tau lepton were determined with an accuracy similar to that of the current world average. The Z-boson pair- production cross-section was measured to be in agreement with the Standard Model predictions, as presented in Fig. L3–2. The high-energy predictions of QED were veriﬁed with the measurement of the O(α4) production of muon and tau pairs in two-photon collisions, as displayed in Fig. L3–3.

14 Experimental Physics Division 2 e+e− → ZZ Data e+e− → ZZ Theory e+e− → ZZ → bbX Data + − 1.5 e e → ZZ → bbX Theory

1 Cross Section (pb) 0.5

0 170 180 190 200 210 √s (GeV) Fig. L3–2: Measurements and Standard Model predictions for the e+e– → ZZ and e+e– → ZZ → bbX cross-sections as a function of s .

800

e+e– → e+e–µ+µ–

e+e– → e+e–τ+τ– 600 QED cross section (pb)

400

160 180 200 √s (GeV) Fig. L3–3: The cross-section of the e+e– → e+e–µ+µ– and e+e– → e+e–τ+τ– processes for an invariant mass of the lepton pair, Wγγ , respectively, satisfying 3 ≤ Wγγ ≤ 40 GeV and Wγγ > 2 mτ . The data are compared to QED predictions.

The exploration of the rich field of two-photon interactions was continued by several additional studies. Previous investigations of inclusive hadron production were complemented with measurements of the production of jets and Λ baryons. Baryon pair-production was further studied in proton anti-proton final states, confirming the predictions of the quark–diquark model and excluding those of the three-quark model. A detailed study of ρ0 production at high Q2 with the full LEP data sample was completed. The cross-section for

Experimental Physics Division 15 the process γγ∗ → ρ0ρ0 is well reproduced by the GVDM model and a ﬁt inspired by QCD calculations is in agreement with the observed differential cross-section of the process e+e– → e+e–ρ0ρ0, as presented in Fig. L3–4.

In conclusion, many data analyses were completed in 2003 and important progress was made toward the ﬁnal publication of many important results on W physics, fermion pair-production, and both exclusive and inclusive ﬁnal states of two-photon collisions.

(a) 102 (b) Data 10 GVDM √s = 91 GeV

] 10 ρ-pole 2 < √s > = 195 GeV QCD fit

] 1 pb/GeV [ nb

[ 1

2 γγ –1 σ 10 / dQ ee σ

d –2 10–1 10

10–3 110 1 10 Q2 [GeV2] Q2 [GeV2] Fig. L3–4: a) The cross-section as a function of Q2 of the process γγ∗ → ρ0ρ0 compared to two theoretical models and b) the differential cross-section as a function of Q2 of the process e+e– → e+e–ρ0ρ0. The solid line represents the result of a ﬁt to a form expected from QCD calculations. In both cases, the two- photon centre-of-mass energy Wγγ is in the interval 1.1 ≤ Wγγ ≤ 3 GeV.

OPAL

The OPAL Collaboration consists of groups from Alberta, Birmingham, Bologna, Bonn, RMKI-KFKI Budapest, Cambridge, Carleton, CERN, Chicago, ATOMKI Debrecen, DESY/Univ. Hamburg, Freiburg, Heidelberg, Indiana, Kobe, Queen Mary and Westﬁeld College London, University College London, Manchester, Maryland, Montréal, LMU München, MPI München, Oregon, Rutherford Appleton Laboratory, Technion, Tel Aviv, Tokyo, Victoria, UBC Vancouver, UC Riverside, Weizmann Institute and Yale.

The general-purpose OPAL detector at the LEP e+e– storage ring is used for a wide range of physics studies. After more than eleven years of successful data-taking starting 13 August 1989, the operation of LEP and the OPAL detector was ﬁnally terminated on 2 November 2000. No major detector failures occurred throughout the entire operation: all 9440 channels of the electromagnetic barrel calorimeter were still fully functional, and none of the 19 776 wires in the central Jet Chamber ever broke.

From 1989 to 2000, a total integrated luminosity of 900 pb–1 was collected, with an overall efﬁciency of 90%. Of these data, 700 pb–1 were recorded at energies above the W+W– threshold up to a centre-of-mass energy of 209 GeV. The analyses performed in 2003 used all data available up to the highest energy unless stated otherwise.

16 Experimental Physics Division Standard Model, Heavy Flavour and QCD Studies

Cross-sections and angular distributions for hadronic and lepton-pair final states were measured and used α to determine the electromagnetic coupling constant em at LEP2 energies. In addition, the results were used together with OPAL measurements at 91–183 GeV within the S-matrix formalism to determine the γ–Z interference term and to make an almost model-independent measurement of the Z mass (Fig. OPAL–1). Non- Λ commutative QED would lead to deviations from the Standard Model depending on a new energy scale NC + – → γγ Λ and a unique direction in space. The process e e was evaluated and NC was found to be larger than 141 GeV for all angles η, defined between the unique direction and the rotation axis of the Earth. These are the first limits obtained on non-commutative QED from an e+e– collider experiment.

5 par fit tot had 1.4 j

1.2

0.8

0.6 LEP1 only 0.4 68% CL 0.2 SM

0 LEP1 + LEP2 –0.2 68% CL 39% CL –0.4 91.17 91.18 91.19 91.2 mZ / GeV − tot Fig. OPAL–1: Confidence level contours in themjZ had plane from the S- matrix fits with lepton universality. The dashed curve shows the 68% confidence level contour from the fit to LEP1 data alone, while the full and dotted curves show the 68% and 39% confidence level contours, respectively, from the fit to LEP1 and LEP2 data. The horizontal band indicates the Standard Model value of tot σ jhad . The vertical band is the 1 error on the Z mass from the five-parameter fit which should be compared with the 39% confidence level contour from the S- matrix fit.

+ – + – A study of W W events accompanied by hard photon radiation, Eγ >2.5 GeV, was made. The W W γ cross-section was determined at five values of s . The results were consistent with the Standard Model expectation and provided constraints on the related O(α) systematic uncertainties on the measurement of the W-boson mass at LEP. Finally, the data were used to derive 95% confidence level upper limits on possible anomalous contributions to the W+W–γγ and W+W–Z0γ vertices. Triple gauge boson couplings were measured from W-pair events. Only CP-conserving couplings were considered and SU(2) × U(1) relations were used, zzλ resulting in four independent couplings,kγγ,, g15 and g . Couplings were determined both in separate fits and allowing some of the couplings to vary simultaneously. All results are consistent with the SM predictions.

Experimental Physics Division 17 A study of Z-boson pair production was made with ﬁnal states containing only leptons, (+–+– and +– νν), quark and lepton pairs, (qq+–, qqνν), and only hadrons (qqqq). In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags were used to separate bb pairs from qq ﬁnal states. Limits on anomalous ZZγ and ZZZ couplings and on low-scale gravity with large extra dimensions were derived using an optimal observable method.

A study of b quark hadronization was made using inclusively reconstructed B hadrons. The data were compared to different theoretical models, and fragmentation function parameters of these models were ﬁtted. The average scaled energy of weakly decaying B hadrons was determined to be

± +0.0036 xE = 0.7193 0.0016(stat) ±0.0031 (syst).

∗∗ ∗∗0 ∗ ∗ The decay chain b → B → D 0–νX, D → D +π–, D + → D0π+, D0 → (Kπ or K3π) was identified P + ∗0 (Fig. OPAL–2) and was used to measure the branching ratio. For decays into the J = 2 ()D2 state, an upper limit of 1.4 × 10–3 was placed on the branching ratio at the 95% confidence level. A measurement of the forward–backward asymmetries of e+e– → bb and e+e– → cc events and the average B mixing parameter χ was made using electrons and muons produced in semileptonic decays of bottom and charm hadrons. The results, obtained using neural networks and a maximum likelihood fit, were combined with other OPAL measurements of the b and c forward–backward asymmetries, and used to derive a value for the effective electroweak mixing angle for leptons.

D D ∗ ↓↓1 2

25 OPAL D0 → Kπ and K3π D events = 28.7 ± 8.6 1∗ D2 events = 3.1 ± 6.9 20 Background events = 213.1 ± 16.6 γ = 0.44 ± 0.12 β = 3.8 ± 0.5 15

Events/20 MeV 10

0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 ∆m∗∗ (GeV) ∗∗ Fig. OPAL–2: ∆m distribution for D0 → Kπ and D0 → K3π combined. The superimposed lines show the overall ﬁt and the background ﬁtted shape. The 0 ∗0 expected positions of the D1 and D2 are indicated by the arrows.

Bose–Einstein correlations in π0 pairs produced in Z0 hadronic decays were studied using LEP1 data. The chaoticity parameter and the source radius were obtained. According to Monte Carlo models, the Bose– Einstein correlations largely connect π0’s originating from the decays of different hadrons. Prompt pions formed at string break-ups or cluster decays only form a small fraction of the sample.

18 Experimental Physics Division Higgs and Other Searches

A search for stable and long-lived massive particles of electric charge |Q/e| = 1 or fractional charges of 2/3, 4/3, and 5/3 was made. Within the framework of the Constrained Minimal Supersymmetric Standard Model (CMSSM), a lower limit of 98.0 (98.5) GeV on the mass of long-lived right- (left)-handed scalar muons and scalar taus was obtained. Long-lived charged heavy leptons and charginos were excluded below 102.0 GeV. A search was performed for charginos with masses close to the mass of the lightest neutralino. Upper limits were derived on the chargino pair-production cross-section, and lower limits on the chargino mass in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated supersymmetry breaking scenarios. Searches for R-parity-violating decays of charged sleptons, sneutrinos and squarks were made and limits on the production cross-sections of scalar fermions in R-parity-violating scenarios were obtained. Constraints on the supersymmetric particle masses were also made in an R-parity- violating framework analogous to the CMSSM.

A search for anomalous production of di-lepton events with missing transverse momentum was performed. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. Upper limits were determined on the production cross- section for sleptons (Fig. OPAL–3), leptonically decaying charginos, and charged Higgs bosons. A search was made for pair-produced leptoquarks, which are produced via couplings to the photon and the Z0, and lower limits on masses for scalar and vector leptoquarks were calculated. The results improve most of the LEP limits derived from previous searches for the pair-production process by 10–25 GeV, depending on the leptoquark quantum numbers.

100 0.35

0.3 80

0.25

60 0.2

40 0.15

20 0.1

0.05 0 lightest neutralino mass (GeV)neutralino (GeV) 50 60 70 80 90 100 stau mass (GeV) Fig. OPAL–3: Contours of the 95% CL upper limits on the stau pair cross-section 2 ττχ→ 0 timesBR (ƒƒ1 ) at 208 GeV based on combining the 183–208 GeV datasets assuming a β3/s dependence of the cross-section. The kinematically allowed region lies below the dashed line. The unshaded region at very low ∆m is experimentally inaccessible in this search.

Experimental Physics Division 19 A search for the single production of doubly-charged Higgs bosons was performed and upper limits were ±± derived on hee, the Yukawa coupling of the H to like-signed electron pairs. Additionally, indirect constraints ±± on hee from Bhabha scattering at centre-of-mass energies between 183 GeV and 209 GeV, where the H would contribute via t-channel exchange, were derived for M(H±±) < 2 TeV (Fig. OPAL–4). These were the ﬁrst results both from a single production search and on constraints from Bhabha scattering reported from LEP.

The data from the four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, were used to search for the Standard Model Higgs boson. The results of the four collaborations were combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. A lower bound of 114.4 GeV/c2 was established for Standard Model Higgs boson mass. Upper bounds on the HZZ coupling for various assumptions on the decay of the Higgs boson were set.

0.7 ee H++→ e+e+ 0.6 limit on h 0.5

0.4

0.3

0.2 limit from direct search 0.1 limit from Bhabha scattering excluded by pair production

0 102 103 mH++ (GeV)

Fig. OPAL–4: Limits at the 95% conﬁdence level on the Yukawa coupling hee assuming a 100% branching fraction of the H±± → ee. The direct limit is calculated with the combined results of the two-lepton and three-lepton analyses.

The indirect limit on hee obtained from Bhabha scattering is also shown. The shaded regions for masses below 98.5 GeV are excluded in Left–Right Symmetric models by the OPAL pair-production search.

Two-Photon Physics

The exclusive production of proton–antiproton pairs in the collisions of two quasi-real photons was studied for pp invariant masses, W, in the range 2.15 < W <3.95 GeV. The cross-section measurements were compared with previous data and with recent analytic calculations based on the quark-diquark model. Di-jet production was studied in collisions of quasi-real photons. Jets were reconstructed using an inclusive k⊥-clustering algorithm and a cone jet algorithm. The inclusive di-jet cross-section and angular distributions were measured and the inﬂuence of an underlying event was studied. The results were compared to next-to-leading-order perturbative QCD calculations and to PYTHIA leading order predictions. For the ﬁrst time at LEP the

20 Experimental Physics Division production of prompt photons was studied in the collisions of quasi-real photons. The total inclusive γ production cross-section for isolated prompt photons in the kinematic range of transverse momentum pT > γ 3.0 GeV and pseudorapidity |η | < 1 was determined. Differential cross-sections were compared to the predictions of a next-to-leading-order (NLO) calculation.

Summary

In total, 385 papers over a wide range of topics have been published since 1989. Of the 19 papers which were published or were accepted by journals in 2003, 15 reported results obtained using data up to highest energies of 209 GeV. In addition, many OPAL results were presented at conferences throughout the year. At the major summer conferences in Aachen (EPS) and at Fermilab (Lepton–Photon), OPAL contributed 60 papers. In total, 41 talks were given at international conferences. As in previous years, students contributed strongly to the physics output, and 11 PhD theses were completed.

The analysis of OPAL data will still continue over the next years. Major results from various searches were published in 2003. Standard Model physics and related topics will be ongoing for a longer time. Twenty-six PhD students are still working on OPAL data analysis and expect to complete their theses within the next few years. More than 50 physics analysis projects are still ongoing.

The LHC Programme

ATLAS (A Toroidal LHC Apparatus)

Scientific Potential

ATLAS is a general-purpose experiment for recording proton–proton collisions at the LHC. The detector design has been optimized to cover the largest possible range of LHC physics: searches for Higgs bosons and alternative schemes for the spontaneous symmetry-breaking mechanism; searches for supersymmetric particles, effects from extra dimensions, new gauge bosons, leptoquarks, and quark and lepton compositeness indicating extensions to the Standard Model and new physics beyond it; studies of the origin of CP violation via high-precision measurements of CP-violating b-decays; high-precision measurements of the third quark family such as the top quark mass and decay properties, rare decays of b-hadrons, spectroscopy of rare 0 b-hadrons, and Bs -mixing.

Overall Layout

The detector, shown in Fig. ATLAS–1, includes an inner tracking detector inside a 2 T solenoid providing an axial ﬁeld, electromagnetic and hadron calorimeters outside the solenoid and in the forward regions, and barrel and end-cap air-core-toroid muon spectrometers. The precision measurements for photons, electrons, muons, τ-leptons and b-quark jets are performed over |η| < 2.5 (muon spectroscopy extends to |η| < 2.7). The complete hadronic energy measurement extends over |η| < 4.9.

Experimental Physics Division 21 Fig. ATLAS–1: The ATLAS facility.

Inner Tracking Detector

The inner tracking detector consists of straw drift tubes interleaved with transition radiators (TRT) for robust pattern recognition and electron identification, and several layers of semiconductor strip (SCT) and pixel detectors providing high-precision space points. The TRT straws have been produced and the straw reinforcement has been completed. The TRT barrel module production is completed, the end-cap module production is on-going. The front-end electronics have been prototyped as radiation-hard circuits and the performance before and after irradiation has been verified. The production chips have been delivered and are undergoing final tests. For the two silicon systems the two most central components are the silicon sensors and FE ASICs. The sensor production in completed for the SCT and ongoing for the PIXEL system, and overall the quality is good. Both systems have confidence that their designs can handle the LHC operation conditions. The radiation-hard electronics for the SCT has been built into hybrids, assembled to barrel and forward SCT modules, and evaluated as larger systems. The barrel module series production is at the 50% level and the endcap module production is approaching the 5% level. The PIXEL readout electronics has been successfully transferred to radiation-hard processes and the production version of the crucial FE chips evaluated. The support structures, hybrids, and cooling for both systems are being produced. The macro-assembly of staves, barrels and disks with final modules are being prepared and these many-module systems are the next important steps for the SCT and PIXEL system assemblies. The ID integration preparation in the SR1 surface building at CERN is progressing well. The area is ready to receive the first TRT and SCT parts while the PIXEL parts will arrive in 2005. The tracker operates in a 2 T magnetic field provided by the superconducting central solenoid which has been at CERN since 2001. In 2003 the preparations for inserting the solenoid in the liquid argon cryostat were completed as well as the set-up for the final on-surface testing of the entire system. The power and cryogenic services and controls for the solenoid are tested and accepted. The next step is the integration of the solenoid into the LAr barrel cryostat and a combined system test in spring 2004. The final installation of the integrated system in the cavern is planned for the end of 2004.

22 Experimental Physics Division Calorimeter

The electromagnetic calorimeter is a lead-LAr sampling calorimeter with a ﬁne granularity ﬁrst sampling for shower pointing and π0 rejection and a pre-sampler layer immediately behind the cryostat wall for energy recovery. The end-cap hadronic calorimeters also use liquid argon technology, with copper absorber plates. The end-cap cryostats house the electromagnetic, hadronic and forward calorimeters (tungsten-LAr sampling). The barrel hadronic calorimeter is an iron-scintillator sampling calorimeter with longitudinal tile geometry.

In 2003 as the last of the detectors of the LAr system, the forward calorimeter has taken test beam data with series modules. The results are very satisfactory and compatible with Monte Carlo results. Results of the previous beam runs of the other LAr detectors are being prepared for publication; two papers have been published in Nuclear Instruments and Methods. During 2003 the module assembly of the three types of modules of the forward calorimeter has proceeded at the foreseen rate, the modules for both end-caps have been finished and one half cold-tested at CERN. The series production has been completed for the hadronic end-cap calorimeter. Production of cold electronics is finished. Integration of the modules into wheels was completed to 90%. For the electromagnetic calorimeter, assembly of series modules has continued and about 90% have been assembled. The series production of the mechanics as well as of the electrodes has been finalized with good rate and efficiency. Integration of the two barrel wheels was successfully completed. One of the two end-cap wheels was assembled. A major step forward was made in the fabrication of the barrel and end-cap cryostats as well as in the final design and continued production of the cryogenic system. The barrel cryostat has been filled with the two barrel wheels. It is in preparation for the commissioning cold test. Both end-cap cryostats have been accepted by ATLAS. One of the end-caps was integrated with presampler, electromagnetic end-cap, and two hadronic end-caps. All feedthroughs for both barrel and end-cap have been installed in the cryostats. Finally, the various parts of the radiation-tolerant electronics continued through a large number of design reviews and PRRs. The production of critical parts in radiation-tolerant technologies continued and is close to completion. Final radiation-hard prototypes are available for acceptance tests. Major system tests both for the front-end and the back-end are in progress. Their results will lead to the final PRR in spring 2004. For the tile calorimeter two out of three cylinders have been assembled on the surface. In April 2003 one of the two extended barrels was completed followed by the pre-assembly of the central barrel in October. The weight of the LAr cryostat has been simulated by a dummy weight structure. The preparation of the modules of the second extended barrel for the assembly is ongoing. About 25% of the drawers with the tile front-end electronics have been produced and inserted into modules and tested. Design and integration works of the low-voltage power supplies have continued. Most of the services (cables and pipes) have been identified and the procurement started. The first test routing of the services was done and first cosmic-ray signals have been detected with assembled barrel modules. The calibration of the tile calorimeter modules in standalone mode in the test beam was completed in 2003.

Muon Spectrometer

The Barrel and End Cap Toroids (ECT), which provide the magnetic field for the muon detectors, are in production in industry. The production in industry of the Barrel Toroid components is practically finished. At CERN the cold mass and cryostat integration work is progressing and all cold masses are integrated. Already two coils are in their final stage of cryostat integration. The production of the installation tools and warm structure components is under way and substantial parts of the system have arrived at CERN. The two 11 m

Experimental Physics Division 23 diameter vacuum vessels for the ECTs arrived and the first-stage integration of thermal shields and super- insulation is completed. Next will be the arrival of the complete cold masses. The first ECT cold mass is in its final stage of assembly and will arrive at CERN in early 2004. The manufacture of the required cryogenic, power and control systems, partly in industry, partly at CERN, is progressing well. The helium refrigerators and associated equipment like compressors, gas storage and distribution systems are already installed and under commissioning. The installation of the bedplates and feet that will carry the magnet system is nearly complete and the preparation for receiving the first coils in the cavern is in progress. The toroids will be instrumented with Monitored Drift Tubes (MDT) except in the very forward inner region where Cathode Strip Chambers (CSC) will be used. Resistive Plate Chambers (RPC) in the barrel and Thin Gap Chambers (TGC) in the end caps provide the muon trigger and second coordinate measurement for muon tracks; both kinds of detector have good time resolution. During 2003, the emphasis was placed on running the chamber production of all the muon detectors, and the cruising speed for the full production was achieved. For the trigger chambers, the TGCs continued production; a total of 2765 chambers have been constructed, out of a grand total of 3600 chamber (77%). Furthermore, 57% of the chambers produced have been fully tested with their final electronics in a cosmic-ray set-up and in a high radiation environment. For the RPC production, over 3400 gas volumes, out of a total of 4000, have been produced and over 400 chambers, containing typically four gas volumes have been constructed. For the tracking chambers, in the case of the MDTs, a total of 850 chambers (78% of the non-staged chambers) have been constructed. Forty per cent of the constructed chambers are also equipped with all the gas services and Faraday cages. The non-staged part of the CSCs production has been completed.

Trigger and Data Acquisition

The trigger has three hierarchical levels. The Level-1 Trigger System uses information from the calorimeters and from the muon-trigger chambers to search for high-transverse momentum muons, electrons, photons, isolated hadrons (and hadronic tau decays) and jets, and large missing and total transverse energy.

Development of the level-1 trigger is well advanced, and full functionality prototypes of custom integrated circuits and many types of electronic modules are being evaluated. Tests of full processing chains for the level-1 calorimeter and muon triggers are being mounted. Successful tests of the muon trigger were made in September 2003 using a test beam with 25-ns time structure. Production has started for some of the on- detector electronics for the muon trigger.

The high-level trigger (HLT) system, comprised of the Level-2 Trigger (LVL2) and Event Filter (EF), provides the final selection of event candidates. The level-2 trigger processes information from regions of interest identified by the first level, accessing the data from different detectors sequentially, making early rejection where possible. The Event Filter accesses data from the whole event. The Data Acquisition systems (DAQ) are the DataFlow and Online Software. The former receives, buffers, and transports partial (the so called ‘region of interest’) or full event data from the detector to the HLT and finally to mass storage for the selected events. The Online Software provides overall control, configuration, and monitoring.

The overall system architecture was presented in the HLT/DAQ/DCS Technical Proposal in 2000. This architecture has since been further developed and completed. Its design has been documented in the High Level Trigger, Data Acquisition and Controls Technical Design Report, submitted in June 2003 to the LHCC and recommended for approval in November. The architecture has been validated via extensive testing on a

24 Experimental Physics Division number of testbeds, whose results allowed the final choice of a few technical and architectural options, in particular in the areas of network organization and Read-Out System. The configuration of the custom modules in the DataFlow, the point-to-point link from the detectors to TDAQ (SLink), and the Read-Out Buffer unit (ROBIN) have also been finalized. Their Final Design Reviews are scheduled between March and May 2004. The overall system of both the DataFlow and Online systems has been measured on a full vertical slice of the size of ~10% of the final system, as well as with large-scale tests on the Lxshare cluster at CERN (involving ~200 PCs) and in the test beams of the ATLAS detectors. For the HLT, a common trigger selection software system has been designed for use in both the LVL2 and EF systems. The design makes maximal use of ATLAS offline concepts and packages while respecting the stricter constraints of the trigger environment. The close interaction between the trigger and offline groups for this work has proved to be mutually beneficial to both projects. Dedicated studies, endurance tests, and performance measurements of the specific LVL2 and EF aspects of the system have been performed on PC testbeds of varying size and are presented in the Technical Design Report. A small farm of PCs running the Event Filter system was implemented in the testbeam runs for the muon detector and successfully used for both detector monitoring analysis and some simple event selection. More comprehensive testing and use is planned for the testbeam running in 2004.

The Detector Control System (DCS) provides a distributed control system for the ATLAS apparatus. Its key hardware and software components, including a commercial Supervisory Control and Data Acquisition (SCADA) system and a radiation-tolerant, microprocessor-based Front-End system, the Embedded Local Monitor Board (ELMB), are being widely used for developing control and monitoring applications for all ATLAS detectors. The mass production of the ELMB has started. The architecture of the Back-End system has been deﬁned using the SCADA, organized in a 3-level hierarchy, and a prototype is being set up for the 2004 testbeam. The ﬁrst infrastructural services like rack control and Detector Safety System are being prepared for deployment later in 2004.

Computing

At the beginning of 2003 the organization of the Software & Computing project was restructured, in order to be better adapted to the current phase of software development and deployment. The new Computing Management Board, which includes in addition to the Computing Coordinator, the Software Project Leader, the Grid, Data Challenge and Operations Coordinator, the Database Coordinator, the chair of the International Computing Board and of the Computing Model Working Group, the Planning Coordinator, the Physics Coordinator and the T-DAQ Liaison, organizes and oversees all computing activities.

Software development has continued with the completion of the full GEANT4-based simulation suite, the new digitization procedures in ATHENA, the second cycle of design of OO/C++ reconstruction software, and the implementation of the POOL-based persistency mechanism. The software development and deployment environment and infrastructure have been considerably improved in order to ease the distribution to external labs and the deployment on Grid infrastructures.

Data Challenge 1 was completed with the reconstruction in spring 2003 of all the events produced earlier. A sizeable fraction of this work was done on Grid infrastructure, NorduGrid in Scandinavia and APG (ATLAS Production Grid) in the USA. Extensive tests and partial productions were run by ATLAS collaborators with ATLAS software on the European DataGrid testbeds and, more recently, on the ﬁrst installations of the LCG-1 system.

Experimental Physics Division 25 Installation and Commissioning

The main experimental cavern, shown in Fig. ATLAS–2, was handed over by the civil engineers in May 2003. A special ceremony took place in the presence of the president of Switzerland. Since then the ATLAS installation work has started. The first phase included the installation of the necessary infrastructure (painting of the cavern, cranes, ventilation system, metallic structures around the experiment, forward shielding, cryogenics lines, various support structures, cryogenics tanks, temporary electrical infrastructure, etc.). All this complex work (pending some finishing of the ventilation work on the ceiling of the cavern) was achieved by the end of December according to specifications and schedule. The dimensions of ATLAS, the height of the cavern, the important amount of subcontractors working in parallel (~50), had made the execution of this work very intense and challenging. In October ATLAS started the installation of the main detector supports: a large stainless-steel structure, placed in the centre of the cavern and manufactured in Russia. This will allow the start of the installation of the various detector components in early 2004.

Substantial progress was also made in the service cavern. After completion of a large, 3-ﬂoor metallic structure, two large He refrigerators were installed and connected, all rooms were constructed. Most of the pipe work for ventilation, gas, cooling water and cryogenics has been completed. The two large rooms that will host the detector electronics have been instrumented with all necessary infrastructure (cooling water, HVAC, cable trays) and are ready for the proper electronics racks installation. The secondary cooling plant was installed and is now instrumented and ready for commissioning.

Fig. ATLAS–2: Installation status.

During 2003 all surface buildings were also completed by CERN-ST/CE and delivered to ATLAS. All of them have been equipped with the necessary infrastructure by the CERN technical sector. In all of them the installation of the speciﬁc services and equipments has advanced very well and according to the initial planning. At the end of 2003 the external cryogenics building and the cooling infrastructure (air and water) entered the commissioning phase.

26 Experimental Physics Division Organizational Issues and Schedule

The ATLAS Collaboration consists of 151 participating institutions (October 2003) with about 1700 scientific collaborators. A Memorandum of Understanding signed by all participating funding agencies specifies the construction deliverables expected from each participating institute. Another Memorandum of Understanding has been agreed for the operation phase. The whole construction project is described in a baseline schedule linked to the installation schedule. The baseline schedule contains milestones that are regularly monitored by the experiment management. By the end of 2003, about 60% of the construction milestones were met, and 80% of the construction payments were made. A new estimate of cost to completion showed that 68 MCHF supplementary funding is required. Commitments for about two-thirds of this have been received, thanks to the effort of many funding agencies. Another resource issue that became apparent during 2003 was a deficit in software engineers for the central computing effort. This has also been addressed with the funding agencies with good indications for its solution. Continued interactions between ATLAS and the agencies are expected during 2004 to further address these issues. Within the constraints of available resources a staging scenario giving a consistent initial detector able to meet the needs of the initial low-luminosity physics run, has been integrated into the planning. The global detector commissioning is expected to begin in autumn 2006. For more information, please consult the Web site http://atlas.ch and the newsletter http://aenews.cern.ch .

CMS (Compact Muon Solenoid)

The CMS Collaboration consists of 2030 scientists and engineers from 162 institutes in 36 countries (February 2004).

All detector sub-systems have started construction. CMS is following an assembly sequence, v33, that allows a complete detector (except for ME4, some RPC chambers at low angles and the pixel detector that will be installed after the LHC pilot run) to be ready for the ﬁrst LHC beam in April 2007. A brief description, together with the status, of each element of CMS is given below.

Civil Engineering

Civil engineering works at Point 5 (located at Cessy, France) are advancing well. The second phase of the construction of the surface hall has started with the removal of the crown of the experiment shaft and the extension of surface SX slab. The surface control room building, SCX, should be delivered to CMS in January 2005. The underground cavern UXC5 (for the experiment proper) is expected to be given to CMS in summer 2004. The underground cavern USC5 (for the counting rooms and services) will be accessible in April 2004 when the installation of infrastructure will start. The CMS experiment cavern will be ready to receive detector elements around September 2005.

A problem of water ingress in the two shafts, PM54 (services) and PX56 (experiment) has appeared. Ingress in PM54 is small and no sensitive equipment will be below this shaft. It will not be repaired though the situation will be reviewed in Spring 2004. On the contrary PX56 will be repaired immediately after the delivery of the UXC5/SX5 complex in Summer 2004.

Experimental Physics Division 27 Installation

Services (gas and cooling pipes etc.) for Muon CSCs have been installed on all endcap disks, and this work will continue for Muon DTs and Muon RPCs on the barrel wheels.

Magnet

The detector (Fig. CMS–1) will be built around a long (13 m), large bore (inner diameter of 5.9 m) and high-ﬁeld (4 T) superconducting solenoid. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m, and a total weight of 12 500 tonnes. All ﬁve barrel rings and six endcap disks (three for each endcap) of the return yoke have been assembled in the main surface building (SX5) at Point 5. The yoke also acts as the principal support structure for all the detector elements. All metallic structures have been assembled around the rings and disks, for the support of electronics, cryogenics etc. The outer vacuum tank has been installed in the central barrel ring, while the inner vacuum tank is currently in a vertical position equipped with the inner thermal shield. The dummy thermal load and the 6000 litre cryostat have been installed on the central wheel and the outer cryogenics will be tested in early 2004.

Current leads have been manufactured and tested to 20 kA at Saclay. The power converter has been delivered and the power circuit will be tested soon.

1.23 % 0.00 m 6.61 m 3.954 m 1.268 m

10.83 m .8cm .5cm η = 1.1 η = 1 η = 0.5 g 7.430 m 7.380 m MB/2/4 MB/1/4 MB/0/4 Y 6.955 m 7.000 m YB/2/3 YB/1/3 YB/0/3 MB/2/3 MB/1/3 MB/0/3 ME/1/3 5.975 m Z η = 1.479 YB/2/2 YB/1/2 YB/0/2 MB/2/2 MB/1/2 MB/0/2 ME/4/2 ME/3/2 ME/2/2 YB/2/1 YB/1/1 YB/0/1 4.905 m MB/2/1 MB/1/1 MB/0/1 4.020 m 3.800 m

ME/1/2 CB/0 YE/3 η 2.950 m = 2.4 YE/2 2.864 m 2.700 m

YE/1 1 HE/1 HB/1 1.932 m ME/4/1 ME/3/1 η = 3.0 ME/2/1 1.700 m 1.790 m 1.750 m ME/1/ EB/1 1.290 m 1.185 m HF/1 EE/1 SB/1 η = 5.31 0.440 m 0.00 m SE/1

9.75 m 8.49 m 7.24 m 6.68 m 6.45 m 5.68 m 4.25 m 3.88 m .25cm 14.96 m 14.56 m 14.53 m 10.63 m 2.935 m 0.000 m 10.91 m 10.86 m

Fig. CMS–1: Transverse view of CMS.

All 21 lengths of the reinforced conductor (superconducting strands, pure Al insert and Al alloy reinforcement) have been produced at Techmeta, France. Impregnation of the first two of five coil modules (CB-2, CB-1) has been completed in Ansaldo (Genova, Italy). CB0 has been wound and is ready for impregnation. Work is advanced on the final two mandrels. All the coil modules should be delivered to CERN by autumn 2004. The magnet test in the surface building should be completed by Autumn 2005.

28 Experimental Physics Division Inner Tracking

The inner tracking sub-system has been designed with the principal objectives of efﬁcient reconstruction and precision momentum measurement of high-transverse-momentum charged tracks. The tracking volume is given by a cylinder of length 6 m and diameter 2.6 m. About 210 square metres of silicon microstrip detectors (10 M channels) provide the required granularity and precision in the bulk of the tracking volume. Pixel detectors (~67 M channels) placed close to the interaction region improve measurements of the track impact parameters and allow accurate reconstruction of secondary vertices.

The microstrip tracker comprises an inner barrel (TIB), inner discs (TID), outer barrel (TOB) and endcaps (TEC). All module components have entered production. One-third of the sensors from Hamamatsu (Japan) have been delivered. The quality of the STMicroelectronics (Italy) sensors is being assessed. Several hundred modules have been assembled comprising silicon sensors, support mechanics, and front-end electronics. Module production was delayed by difﬁculties in the industrial manufacture of hybrids suitable for automatic bonding but has now restarted.

System tests of the tracker modules (TEC petal, TOB rod, TIB shell) were successfully carried out in May 2003 using the ‘25 ns bunched’ beam. These involved modules with the full electronics chain, the analog optical data links, together with the ﬁnal control system (including ASICs and the digital optical link) both in laboratories and in particle beams. A series of prototype readout modules (FED) have been under test since the beginning of 2003. The manufacture of pre-series FEDs will commence in Q1-2004. The schedule foresees the integration of the TIB, TOB, TEC and TID in the second half of 2005.

Good progress has been made on pixel electronics and sensors. The 0.25 µm deep-sub-micron (DSM) readout chip (ROC) was received in August 2003. The chip works well. DSM ROC allows a better performance, in terms of spatial resolution, noise, power consumption, lifetime and data losses, than was possible with the DMILL ROC. Several prototype modules (sensors bump-bonded with DMILL electronics chips) have been tested. Final tooling for mass-production is now being developed. Pre-production modules using DSM ROCs will be made in Q2-2004 and the mass production should start in Q1-2005.

The Muon System

Centrally produced muons are measured three times: in the inner tracker, after the coil and in the return flux. They are identified and measured in four identical muon stations inserted in the return yoke. Each muon station consists of many planes of aluminium drift tubes (DTs) in the barrel region and cathode strip chambers (CSCs) in the endcap region. The four stations include resistive plate chamber (RPCs) triggering planes that also identify the bunch crossing and enable a cut on the muon transverse momentum at the first trigger level.

Barrel Drift Tubes: The three sites at CIEMAT (Madrid), Aachen and Legnaro (Padova) are continuing to produce chambers at the required rate of 18 chambers/year/site. The production at the fourth site, Torino, will start at the beginning of 2004. Over a hundred chambers (40%) have been assembled and over seventy chambers have been delivered to CERN. The chambers are ‘dressed’ (with external piping and cabling) in the CERN-ISR area and ~20 chambers will be installed in the yoke wheels in Q1-2004. A chamber with the ﬁrst ‘minicrate’ (housing external electronics) was successfully tested in the 25-ns-bunched beam in May 2003. The mass production of minicrates has started after a successful Electronics System Review (ESR) in November 2003.

Experimental Physics Division 29 Endcap Cathode Strip Chambers: All the chambers (482 including spares) have been assembled in sites in China (IHEP, Beijing), Russia (Dubna, PNPI, St Petersburg) and the USA (FNAL). Most have been tested with on-board electronics in the FAST (Final Assembly and System Testing) sites at the Universities of Florida and UCLA, Dubna, PNPI and IHEP. Over a quarter of the chambers are at CERN and after ﬁnal tests about a ﬁfth (90 ch) have been installed of the magnet yoke disks. Station ME4/1 has been reinstated and is not staged anymore.

Barrel RPCs (RB): The gap and chamber production is proceeding well. Over 100 chambers (20%) have been assembled and ~70 are at CERN. Two final RB1 chambers have been operating in the gamma irradiation facility (GIF) for over six months and so far have integrated a charge corresponding to approximately the first five years of LHC operation. Good performance has been observed.

Endcap RPCs (RE): An RPC gap factory has been installed in Korea and mass gap production, using Italian Bakelite and linseed oil, has started. The gaps will be sent to Pakistan and to CERN (for a Chinese team) to be assembled into chambers.

Alignment: The alignment bench for the ‘calibration’ of reference points with respect to the wire position in the DT chambers is being used at the ISR. The design for the ‘Link’ system (tracker-muon) has been changed and improved.

The Electromagnetic Calorimeter (ECAL)

Scintillating crystal calorimeters offer the best performance as far as electromagnetic energy resolution is concerned. Lead tungstate (PbWO4) has been chosen because it offers the best prospects of meeting the diverse requirements for operation at the LHC. The scintillation light is detected by silicon avalanche photodiodes (APDs) in the barrel region (EB, |η| < 1.48) and vacuum phototriodes (VPTs) in the endcap region (EE, 1.48 < |η| < 3.0). A preshower system (ES) is installed in front of the endcap calorimeter (1.579 < |η| < 2.6) to improve rejection of neutral pions.

About 25 000, out of 62 000, barrel crystals have been delivered and are being used to construct modules (each comprising 400 or 500 crystals) in CERN and Rome. Forty modules, out of 144, have been produced. Seven bare supermodules (SM) (1700 crystals) have been assembled. A delay in crystal production has been caused by the slow transition to ‘2in1’ (2 crystals from one boule) production. The new schedule now has the last barrel crystal being delivered in Q4-2005. The bulk of endcap crystal production will now occur after the completion of barrel production.

Delivery of the 140 000 APDs is due to terminate in Q1-2004. Over 6000 VPTs have been delivered and tested to 1.8 T.

Much progress was made in 2003 on DSM front-end electronics (made to be baseline in mid 2003). Several DSM ASICs (FENIX that generates the EB/EE trigger primitive, MGPA – EB/EE preamplifier, AD41240 ADC, PACE3 – ES front-end, K-chip – ES concentrator) returned in May 2003 from fabrication. The EB/EE DSM system was tested in beam in October 2003 and returned a better performance with a significant reduction in cost than the previous FPPA-based system. An ESR held in early October 2003 authorized the launch of pre-series production (yielding sufficient electronics for 3 SMs). The first SM

30 Experimental Physics Division equipped with the ﬁnal electronics will be tested in beam in autumn 2004. The ECAL schedule foresees the calibration of at least 3 SMs in beams in 2004 and one endcap Dee in 2006. It is hoped that the ECAL can be completed and commissioned by April 2007.

Pre-shower: Mass production of the silicon sensors has started in Russia and India (about 1/3rd of sensors have been produced and tested) and is starting in Taiwan. Very encouraging performance has been attained with the DSM chips (PACE3 and K-chip). A new engineering design, constructing the ES as two ‘Dees’ similar to the EE, was endorsed in early 2003. This gives ﬂexibility to installation/repair scenarios.

The Hadronic Calorimeter (HCAL)

The HCAL has three geometrically distinct parts. The central pseudorapidity range |η| < 3.0 is covered by the barrel (HB) and endcap (HE) parts, while the region 3.0 < |η| < 5.0 is covered by the forward calorimeter (HF). In addition there is a tail-catcher in the central barrel ring called HO.

The barrel and endcap brass/plastic scintillator sampling calorimeters sit inside the 4 T ﬁeld of the CMS solenoid. The two HB half-barrels have been assembled in SX5 and are awaiting their readout electronics. Both the endcap absorbers have been mounted and optics (scintillators and ﬁbres) installed. All of the HO optics have been delivered to CERN.

Modules of all geographic parts of HCAL HB, HE, HO and HF were tested in beam in the summer of × 2003. In addition HB, HE and HO were tested with a 7 7 PbWO4 crystal matrix in front. The crack through which the cables pass, from the tracker and ECAL, was scanned. The results will be used to tune GEANT4- based simulation. Preproduction electronics were used. In 2004 the photodetectors and readout electronics will be installed on HB and HE in SX5 and a ‘ﬂying’ data acquisition system will be used to commission HB and HE.

All 36 steel absorber wedges for the HF have been produced and delivered to CERN. Insertion of quartz fibres (the active medium) into all 36 wedges will be finished in early 2004. The support structures for the two HF have been manufactured in Iran, and the first one will be delivered in early 2004.

Trigger and Data Acquisition (TriDAS)

The trigger and data acquisition consists of four parts: the detector electronics, the calorimeter and muon ﬁrst-level-trigger processors, the readout network, and an online event ﬁlter system.

The CMS level-1 trigger decision is based upon the presence of physics objects such as muons, photons, electrons, and jets, as well as global sums of Et and missing Et (to infer the presence of neutrinos etc.).

The level-1 trigger system is initially expected (at low luminosity) to reduce the bunch-crossing rate of 40 MHz to an event rate of 50 kHz. Each physics event (1 Mbyte large) is contained in about 600 front-end buffers. The High Level Trigger (HLT) System is expected to reduce the level-1 event rate by a factor 1000, leading to a maximum rate of sustainable physics events of 100 Hz for a nominal level-1 event rate of 100 kHz. The physics algorithms of the HLT are implemented in software which is executed in a conventional

Experimental Physics Division 31 computer. A large number of such computers (~1000), organized in a so-called ‘ﬁlter farm’, are required to process events at the rate delivered by the level-1 trigger.

The Data Acquisition (DAQ) System assembles event fragments from the ~600 front-end buffers into complete events, which are then delivered to the HLT for processing in the filter farm. This ‘event building’ is implemented with high-capacity networks, which connect ~600 data sources to 500 data sinks that act as interfaces to the filter farm. The absence of commercial, very large, high-capacity network switches led to an event builder architecture in two stages that are decoupled through sizeable buffer memories. In the first stage, 64 front-end builder networks assemble event fragments from 8 or more data sources into event super- fragments that are buffered in readout units. In the second stage, eight 64 × 64 port switches assemble super- fragments from the readout units into full events, which are then ready for processing in the high-level trigger farm. The choice of carrying the HLT process in a single farm has been validated.

A key characteristic of this design is the modularity that allows a staged deployment. The system can operate with full functionality with fewer than eight networks in the second stage, albeit at reduced capacity. The initial DAQ can thus be tailored to the expected luminosity at LHC start-up while keeping the possibility to grow with time to meet the requirements of the full LHC design luminosity. This provides maximum ﬂexibility in the online physics selection process.

Level-1 Trigger: Many full-function prototypes have been manufactured and ﬁnal validation tests are being done. Integration tests of detector primitive generators, trigger system, and DAQ are underway. Tests with structured ‘LHC-like’ beam (25 ns bunched beam) have been very valuable to establish latencies. Software is now being developed for testing and operation.

DAQ: The Data Acquisition and High-Level Trigger Technical Design Report was approved by the LHCC. FrontEnd Readout Link (FRL) prototype boards are being tested and preproduction has started. FED and Readout Builder (RB) demonstrators are running at CERN. The ﬁrst event ﬁlter sub-farm prototype is running under realistic conditions

Software and Computing

The CMS Software and Computing Project is organized as a single Project called CPT: Computing and Core Software (CCS), Physics Reconstruction and Selection (PRS), and software and computing aspects of TriDAS.

The emphasis of the CCS group has moved to the preparation of the Computing TDR and to the Data Challenges required to validate key features of the Computing Model. A few tens of million events have been simulated using OSCAR (simulation using GEANT4) and POOL (persistency). The data challenge in spring 2004 (DC04) is designed to test the initial LCG-GRID implementation. The data challenge itself will involve the reconstruction of the simulated data at a prototype Tier0 at CERN and the distribution of appropriate datasets to the regional Tier1 and Tier2 centres with a set of real-time analysis tasks operating at the remote centres. The scale of the challenge is set to be 25% of LHC startup conditions.

CMS has placed priority on a full understanding and veriﬁcation of the Higher Level Triggers (HLT). Since CMS does not employ distinct physical intelligences for the would-be level-2 and level-3 triggers, but

32 Experimental Physics Division only a single processor farm, the task of selecting events is intimately linked with that of reconstructing the τ associated detector information online. The four PRS groups (electron/photon, muon, jet/missing Et, and b/ vertexing) aim to develop the reconstruction and selection procedures (algorithms and software) starting from the output of the level-1 trigger to the ﬁnal event-recording on mass storage.

‘Full detail’ physics studies have started that employ GEANT4 simulation and the OO reconstruction and analysis packages. The already existing PRS groups have been augmented by four new Analysis PRS groups (labelled SM (Standard Model), SM and SUSY Higgs, Beyond the SM and Heavy Ions) to prepare for physics. A Physics TDR will be written for the end of 2005. The Physics TDR will be a test of validity/ readiness of CMS to extract initial physics.

The LHC Computing Grid (LCG) project was launched in 2001 and CMS participated heavily in this joint project in 2003. The aim is to allow the possibility of data analysis in a distributed environment, where physicists are scattered all over the world. The optimum mix of storage, networking, and processing has to be ascertained as technology develops.

Physics

The physics performances of the individual sub-detectors are summarized below:

TRACKER: in high-pt events the track-finding efficiency for tracks not interacting in the tracker is >96% |η| ∆ for pt > 2 GeV and within < 2.5. The momentum resolution is: pt/pt ~ 0.15 pt + 0.5% (pt in TeV). The use of pixel detectors close to the interaction point leads to b-tagging efficiency of ~50% for a rejection of ~100 against non-b jets.

ECAL: the mass resolution for a 100 GeV Higgs boson decaying into two photons is found to be 650 MeV at low luminosity and 690 MeV at high luminosity. A large fraction of the conversions are recovered when an appropriate energy-clustering algorithm is used.

HCAL: the missing energy resolution is not much degraded w.r.t. an ideal Gaussian detector response. The jet–jet mass resolution for Ws from heavy Higgs is found to be about 8.5 GeV. In the search for a low-mass Higgs boson an interesting channel is qq → qqH (H → tt). Maximization of the S/N requires dedicated τ-triggers, efﬁcient forward jet tagging, and good missing transverse energy resolution to enable cuts to be placed as low as 30 GeV.

MUONS: the excellent momentum resolution of the muon and inner tracking system is reﬂected in a mass resolution of about 1 GeV for a 150 GeV Higgs boson decaying into ZZ*, each of which in turn decays into two muons.

There are strong physics arguments for supersymmetry (SUSY). Squarks and gluinos weighing up to 2 TeV can be detected, using as signature events with one or more charged leptons, missing transverse energy, and two or more jets. Sleptons weighing as much as 400 GeV can be found by looking for events without hadronic jets, but with lepton pairs and missing transverse energy having distinctive kinematic characteristics. Three-lepton states are particularly promising for the detection of charginos and neutralinos. In many cascade decays a heavier neutralino is produced that subsequently decays into the lightest one with the emission of a

Experimental Physics Division 33 pair of charged leptons. For low to moderate values of tanb the spectrum of the di-lepton invariant masses shows a strikingly sharp end-point determined by the difference in neutralino masses. This feature can be used to select and almost fully reconstruct some events yielding, for example, the mass of the bottom squark.

The above studies of speciﬁc SUSY models indicate that it is possible to detect a large fraction of the expected SUSY spectrum in CMS. Within the SUGRA models it should be possible to determine the fundamental parameters at the GUT scale.

Studies were performed to explore the physics reach of CMS during the ﬁrst year of LHC operation. With an integrated luminosity of 10 fb-1 per CMS/ATLAS the SM Higgs can be discovered up to a mass of 1 TeV. The SUSY reach can be characterized by the discovery of squarks/gluinos for masses less than about 2 TeV.

Detailed studies have been carried out of the capabilities of CMS for heavy-ion physics. CMS is found to 0 γ be an excellent detector for high-pt probes (quarkonia, jet quenching, photons and Z ), correlations (jet– , jet– Z0), and global event characterization (energy ﬂow, charged particle multiplicity, centrality) etc.

A plan for the CMS Physics Technical Design Report, to be submitted at the end of 2005, has been drawn up. CMS will produce two volumes:

– Volume I: Detector response, physics objects, calibration and parametrization

– Volume II: High-level analyses, e.g. Higgs, SUSY, extra dimensions etc.

– Part I: (Small) number of full analyses demonstrating how we can do physics

– Part II: General physics topics (will be done with full simulation or detector parametrization) demonstrating what physics we can do.

ALICE (A Large Ion Collider Experiment)

ALICE is a general-purpose, heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. The ALICE collaboration currently includes more than 900 physicists and senior engineers – from both nuclear and high-energy physics – from about 80 institutions in 30 countries.

The detector is designed to cope with the highest particle multiplicities anticipated for Pb–Pb reactions

(dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and p–nucleus), which provide reference data for the nucleus–nucleus collisions.

ALICE (see Fig. ALICE–1) consists of a central part, which measures event-by-event hadrons, electrons and photons, and of a forward spectrometer to measure muons. The central part, which covers polar angles from 45° to 135° over the full azimuth, is embedded in the large L3 solenoidal magnet. It consists of an inner tracking system (ITS) of high-resolution silicon detectors, a cylindrical TPC, three particle identiﬁcation arrays of Time-of-Flight (TOF), Ring Imaging Cherenkov (HMPID) and Transition Radiation (TRD) detectors, and a single-arm electromagnetic calorimeter (PHOS). The forward muon arm (2–9°) consists of a complex arrangement of absorbers, a large dipole magnet, and fourteen planes of tracking and triggering

34 Experimental Physics Division chambers. Several smaller detectors (ZDC, PMD, FMD, T0, V0) are located at forward angles. An array of scintillators (ACCORDE) on top of the L3 magnet will be used to trigger on cosmic rays.

The experiment was approved in February 1997. The ﬁnal design of the different detector systems has been laid down in Technical Design Reports (TDRs) between mid 1998 and end 2001; the TDR for the online systems (Trigger/DAQ/HLT/DCS/ECS) was submitted in 2003. Construction is well advanced for many of the detector systems and installation of support structures is in progress.

Fig. ALICE–1: Layout of the ALICE detector.

Inner Tracking System (ITS)

The main purpose of the ITS is the detection of secondary vertices (hyperons and heavy quarks) and the stand-alone track ﬁnding of low-momentum charged particles. The system consists of six cylindrical layers of coordinate-sensitive detectors, covering the angular range 90 ± 45°. The innermost planes consist of silicon pixel detectors and silicon drift detectors, whereas the two outer layers are made from double-sided silicon microstrip detectors.

Silicon Pixel Detectors: Several thin ladders, with 150 µm thick chips bump-bonded to 200 µm sensor tiles, have been produced with yield exceeding 99%. The full readout chain, including the multi-chip-module with PILOT ASICs and the custom optical link package, has been validated in laboratory and beam measurements. A full system has been installed and successfully operated with a 158 GeV/A indium beam on a Pb target to test resolution and track reconstruction at high multiplicity. The two construction centres have set up the assembly and mounting equipment and the associated control systems. A half-stave has been produced and is under test.

Experimental Physics Division 35 Silicon Drift Detectors: A first batch of detectors is being fabricated by Canberra on the new NTD silicon and on the old (validated) Wacker silicon in order to check all the production steps. The regular production should start in April/May of 2004 at a rate of 16 good SDDs per month. The engineering run of the final FEE chips (PASCAL-64 and AMBRA-4) was submitted in October 2003 after the successful beam test of the prototypes, performed in August 2003 with the final front-end hybrid layout implemented on a PCB. The test included the compressor chip (CARLOS) and the DDL link. The first mechanical prototypes of the front-end hybrids in Upilex–aluminium have been produced, showing the feasibility of the assembly procedure. The support of the ITS services in the full-scale ITS-integration mock-up is being modified to reduce the amount of material in front of the PMD.

Silicon Strip Detectors: After optimization of the process parameters at the producer, the yield problems with the front-end chip (HAL25) could ﬁnally be solved and the engineering run has produced excellent yield. The silicon strip detector production is ongoing by three suppliers with good results from one manufacturer but not quite satisfactory results with the other two. Several modules have been produced and tested together in the test beam. Preparations for mass production are in progress.

Time Projection Chamber (TPC)

The TPC, the main tracking detector of ALICE, is central to the design of the experiment. Its task is track finding, momentum measurement, and particle identification by dE/dx. In 2003 a major problem had to be solved after discovery of a faulty glue joint, which led to the rebuilding of the inner field cage cylinder. The initial delay of about seven months has now been almost recovered from and the assembly of the field cage at SXL2 is now well advanced, with the inner equipment like HV rods, laser system etc. about 50% complete.

The series production of TPC inner readout chambers (IROC) in Bratislava (second half of chambers) has been running smoothly throughout 2003. About 90% of the IROCs are assembled and the production is expected to finish in March 2004. The series production of the larger outer readout chambers has reached 60% and is expected to finish in May 2004. The service support wheel, carrier of the FEE cards, is nearing completion. The front-end electronics of the TPC has entered the mass-production phase. The front-end card was ordered in October 2003 and the first pre-series of 50 cards has been tested successfully; full delivery of the remaining cards is scheduled for June 2004. The readout control unit (RCU) has finished prototyping, the final layout of the motherboard is under way and production will start in May 2004.

Particle Identification System (PID)

Particle identification over a large part of the phase space and for many different particles is an important design feature of ALICE with several detector systems dedicated to PID: a TOF array optimized for large acceptance and average momenta, a small system (HMPID) specialized on high-momentum hadrons, a TRD for electron identification above 1 GeV/c, a small acceptance high-resolution photon spectrometer (PHOS), and a forward muon spectrometer. In addition, the tracking detectors (ITS, TPC, TRD) provide energy-loss measurement for electron and hadron identification.

36 Experimental Physics Division Multigap Resistive Plate Chambers (MRPC) for TOF

The TOF detector, with a total area of about 140 m2 and 160 000 channels, will identify pions, kaons and protons produced in the central region with momentum below about 2.5 GeV/c for pions and kaons, and up to 4 GeV/c for protons. Several test beam periods have been devoted to the test of the new front-end cards equipped with the analog FE ASIC (second and third, final, prototype). The full electronics chain, including FE ASIC, HPTDC (High Performance TDC v.1.3) and a TRM (TDC Readout Module) prototype, has been successfully tested. The results show that the performance of this ASIC chip (‘NINO’) is comparable to or even better than that of the commercial MAXIM components, thus allowing a substantial reduction of the power dissipation. The first prototype of the TOF intermediate module (19 strips) with services (HV+DCS, LV DC-DC converters) has been tested with beam. The TRM has also been successfully tested inside a magnet up to a field value of 5 kG. A multiboard prototype of the Data Readout Module (DRM) has been built and functionality tests have started. Two prototypes of the LV DC–DC converters have been successfully tested in a magnet of up to 5 kG; hence the final decision of using this system has been taken. The 20 000 HPTDC chips have been produced with packaging and testing ongoing.

The ﬁnal tests of two strips irradiated at the GIF with a total charge of 0.0133 C/cm2 (equivalent to between 1000 and 1500 days of Pb–Pb run at LHC with a rate of 50 Hz/cm2) did not show any sign of ageing effects. Moreover, a gas analysis did not show any presence of ﬂuorine; the current drawn by the two chambers was stable and normal along the full period of irradiation.

High Momentum Particle Identification Detector (HMPID)

The HMPID is a proximity focusing RICH using a liquid radiator, in conjunction with a reflective CsI photocathode, evaporated on the pad-segmented cathode of a multiwire proportional chamber. The project is in full production with three modules (out of seven in total) already assembled. Module no. 1 has been successfully tested in beam. The entire batch of Gassiplex FEE cards has been delivered to CERN. The complete set of about 4000 readout DILOGIC-III ASIC chips has been tested showing a yield above 97%. The order to purchase the MCM cards has been launched. The production of the cathode planes has started and a first batch of 12 planes has been delivered. The VUV scanner has been commissioned and used to crosscheck on beam QE measurements. The glove box for mounting the CsI coated photocathode in an inert atmosphere has been delivered and used during the beam test of module no. 1. A detailed engineering design study to define the cradle mechanics has been carried out; and the PRR successfully done in October 2003. Cooling tests on PROTO-3 using a composite panel equipped with water circulation pipes have established the specifications of the cooling system.

The prototype interface to the DDL and TTCRx systems has been produced and tested with the PROTO-3 detector. The detector was operated using the ﬁrst prototype of the ALICE Experiment Control System (ECS) to control and synchronize the Detector Control System (DCS), the DAQ and the Trigger sub-systems. Calibration, electronics conﬁguration, and physics runs have been performed and controlled from the main ECS panel, fully exploiting the bi-directionality of the DDL link.

Experimental Physics Division 37 Transition Radiation Detector (TRD)

The transition radiation detector (TRD) for ALICE will identify electrons with momenta above 1 GeV/c to study production rates of quarkonia and heavy quarks (charm, beauty) near midrapidity. It consists of six layers of xenon/CO2-filled wire chambers preceded by a composite radiator (foam and fibres). The TRD in its final configuration will provide full coverage of the central barrel region of ALICE between TPC and TOF. With the currently available funding, about half of the detector can be installed initially.

Significant work has gone into the quantitative understanding of the production and absorption probabilities for transition radiation photons. Including these results into the simulations has led to a complete description of the energy loss observed in the detectors. The electronics development has made significant progress. The PASA has been fully evaluated and is now undergoing integration tests on the detector in conjunction with the digital readout chip. A second version of that chip has been received containing 21 ADCs, digital filters, registers, and tracklet processors necessary for the trigger capability of the detector. This marks the final step before launching production of the chips. The two chips were assembled together on Multi-Chip Modules (MCMs), and a readout board containing eight MCMs was successfully read out at 120 MHz. Design and prototyping of the Detector Control System (DCS) is completed and the board has been under extensive radiation tests.

Production of the TRD detector has started and about 30% of the radiators have been produced. All necessary tooling for the production of readout chambers was completed and ordered for duplication at the production sites in Darmstadt, Dubna, and Bucharest. Mass production of the profiles, back panels, and readout boards has started. In December the first set of chambers was completed in Heidelberg fulfilling all specifications in terms of leakage current, gain uniformity, and gas tightness.

Photon Spectrometer (PHOS)

The PHOS detector is a single-arm, high-resolution, electromagnetic calorimeter made with lead tungstate π0 η crystals (PbWO4) designed to search for direct photons and to measure and spectra at high momentum.

Production of PbWO4 crystals continues in the North Crystal Co plant, Apatity, Russia. A production rate of about 300 crystals per month is being achieved, which is governed by available funding. Produced crystals are certiﬁed at the test facility of the Kurchatov Institute. Crystal geometry, optical transmission, and light yield are measured. For the time being, in total almost 4500 crystals (more than 25% of the PHOS crystals) have been accepted, of which 500 crystals have been delivered to CERN in 2002, and 3100 crystals in 2003. A 256-channel (16 × 16 array) prototype of the PHOS spectrometer, coupled to an APD with a low-noise preampliﬁer and equipped with a cooling/thermo-stabilization system and an LED monitoring system, was tested with electron and pion beams. Good performance was demonstrated. The PHOS Front-End Electronics (FEE) project has been re-organized, and R&D for the new FEE (based on components developed for the TPC) is under way. Beam tests of two options of the FEE design were performed to measure energy and time resolution; data analysis is under way.

38 Experimental Physics Division Forward Muon Spectrometer

The forward muon arm is designed to cover the complete spectrum of heavy quark resonances, i.e. J/Ψ, Ψ′, Υ, Υ′, Υ′′. It will measure the decay of these resonances into muons, both in proton–proton and in heavy-ion collisions, with a mass resolution sufﬁcient to separate all states.

Dipole Magnet: The infrastructure, including power cabling and cooling pipes, for the preassembly of the magnet in UX25 was completed in April 2003. The preassembly of the magnet could only be started with the beginning of the shipment of the yoke components in October 2003 and will be continued during the ﬁrst quarter of 2004. Both magnet coils were delivered to CERN in September 2003 and the coil supports have been manufactured. The instrumentation of the magnet, i.e. ﬂow-meters, cooling water hoses, has been procured. The design study for the coil manipulation jig is completed. A prototype of the magnet control system is ready for testing in early 2004.

Muon Tracking Chambers: After analysis of the defects discovered on the first quadrant of station 1, a new detector was constructed with increased mechanical stiffness. Tests have shown good performance and mass production has started. The PRR of station 2 was held in June and the first quadrant was successfully tested in the PS in November permitting the launch of the production. Most of the components for the construction of stations 3, 4 and 5 are ready, the four construction sites are fully equipped and the mass production has started. The production of the carbon sandwich frames for the three last stations is ongoing. The electronics PRR was successfully passed and the FEE production has started; however, some problems still have to be solved concerning calibration of the MANAS preamplifiers. A final prototype of the readout board (CROCUS) is currently under test.

Muon Trigger Detectors: The muon trigger is based on single-gap Resistive Plate Chambers (RPCs) made with low resistivity (a few 109 Ω.cm) Bakelite plates and operated in streamer mode. A preproduction RPC completely equipped with FE electronics was tested at GIF (gamma + muons) in summer 2003. The PRR for the detector construction was completed at the end of 2003 and one-third of the gas gaps have been produced. The PRRs for the FE electronics and trigger electronics were completed in 2002 and 2003, respectively. The whole FE chip production (~4000) has been delivered and a production sample of 10% of the FE board is currently being built. The test bench is fully operational. All FPGAs (~1500) circuits for the trigger electronics have been delivered and a call for tender for the printed circuits and cabling will be submitted soon.

Forward Detectors

ALICE uses a number of smaller detector systems (ZDC, PMD, FMD, T0, V0) located at small angles to deﬁne and trigger on global event characteristics; in particular impact parameter and event reaction plane.

The Zero Degree Calorimeters (ZDC) are two sets of hadronic calorimeters located 116 m from the central ALICE barrel on both sides of the interaction. Two neutron calorimeters have already been built and tested. In October 2003 a test was carried out at the SPS with the indium ion beam, whose energy corresponds to 6–7 spectator neutrons in a central collision at ALICE; the measured energy resolution of the calorimeters (~2.9%) agreed with the expectations. Integration of the detector with the LHC infrastructure is progressing.

Experimental Physics Division 39 The Photon Multiplicity Detector (PMD), consisting of a few m2 of pre-shower detectors (a lead converter sandwiched between two planes of cellular honeycomb gas detectors) mounted behind the TPC, will search for non-statistical fluctuations in the ratio of photons to charged particles and measure collective flow and transverse energy of neutral particles. The PMD has been relocated to a position at z = 360 cm from the vertex in order to reduce the background from upstream material. The detector R&D has been completed with the new cell granularity and a pre-production prototype has been assembled and successfully tested using electron and pion beams. The final design has been documented in an addendum to the TDR and production is about to start.

The FMD detector (silicon pad detectors) will measure charged-particle multiplicity over a large fraction of phase space (–5.1 < η < 3.4); the T0 counters (24 Cherenkov radiators with PMT R/O) will provide the event vertex online and the event time with a precision of less than 50 ps; the V0 counters (36 or 72 scintillator paddles with PMT R/O) will be used as main interaction trigger. All systems underwent several successful beam tests in 2003 in order to ﬁnalize the design and validate the performance in preparation for a common TDR to be submitted early in 2004.

Trigger, HLT and DAQ

The Technical Design Report (TDR), produced jointly for the DAQ, HLT, ECS and DCS groups, was submitted at the end of 2003.

Trigger: In 2003 the Local Trigger Unit (LTU) was to be designed and built at RAL in the U.K. However, unforeseen compatibility problems between RAL and Birmingham software delayed the board design and layout was completed only in December 2003. A ﬁrst version for testing should be available before the end of January 2004, with the full production completed by about June of 2004.

High Level Trigger (HLT): Extensive studies have been conducted in order to develop and benchmark the dimuon trigger and the TPC jet trigger in the HLT. Both the TPC cluster deconvolution and the Hough transformation algorithms were further developed and performance studies are ongoing. The interface between HLT and DAQ has been deﬁned and agreed upon. A discrete event simulation framework, based on Ptolemy, was developed. The HLT communication framework was further improved. Several system integration tests have been conducted, in particular showing the fault tolerance of the framework. It has been demonstrated that any node can be lost at any time without the system loosing a single event or even stalling. A task manager was developed, allowing automatic orchestration of jobs on the various computers. The rule- based cluster fault tolerance framework is released and being used at several sites.

Data Acquisition system (DAQ): A first batch of the second generation of Detector Data Link (DDL), based on new opto-electronics components at 2.1 Gbit/s, has been produced for the detector tests and the test beams. The D-RORC (64 bit PCI interface card to the DDL and to the HLT) has been designed and a few prototypes have been produced. It performs according to specifications with a demonstrated nominal bandwidth of 245 MBytes/s. A test of the DAQ software framework (DATE V4) has been performed during the ALICE Data Challenge V with realistic data traffic based on simulated physics data. It has shown that DATE V4 is capable of reaching the performances needed for ALICE with an efficient usage of the computing and network resources and a fair load-balancing between several event-builders. A successful integration of detector electronics readout chain with the DDL and DATE has been realized in collaboration with the ITS drift and the

40 Experimental Physics Division HMPID detectors groups and used during test beams. The design and the implementation of the Experiment Control System (ECS) have been carried on in close collaboration with the teams of the TPC, the HMPID, and the Trigger. A ﬁrst version of the ECS has been integrated with the DAQ run control and the Detector Control System of the HMPID, and used during the test beam. The design of a new package for the monitoring of online data quality (MOOD) has started. MOOD provides a framework for the analysis of data from DATE in the ROOT environment. The new release of the Trigger/DAQ simulation program developed in collaboration with the Trigger project includes reﬁned models of the detector readout and of the trigger system behaviour. It has indicated critical areas for sharing of the DAQ resources between the data streams of different triggers. A solution based on dynamic downscaling of frequent triggers has been simulated and shown to solve the problem.

Detector Control System (DCS): The SCADA system PVSS, which has been selected as software platform for the controls systems of the four LHC experiments, has been improved and a new version is being prepared for release in early 2004. A framework of tools and components has been developed by the Joint Control Project (JCOP), forming the basis of the ALICE DCS back-end system. A major effort has been devoted to further deﬁne the control requirements of the experiment in User Requirements Documents and identify common solutions; a few of them have already been prototyped and tested. The Detector Safety System (DSS) has been prototyped and is ready for installation. A ﬁrst Magnet Control System (MCS) was installed and tested during the powering of the ALICE solenoid in the summer. A software interface between DCS and DAQ has been tested to verify the principle of the Experimental Controls System (ECS) layer.

Offline

The ALICE framework for global reconstruction has been extended and now includes all detectors and the complete reconstructed event information is stored in an Event Summary Data format. The offline group participated actively in the Alice Data Challenge to test the basic ROOT I/O system for its suitability for the storage of raw data at very high rates. For the first time the files have been stored into the AliEn system and monitoring code provided by the HLT project has been included in the simulated online data stream. Preparation for the Physics Data Challenge to be held in the first half of 2004 has taken most of the resources of the Offline Project. This large exercise aims at generating and processing 10% of the data of a standard data-taking year and will involve several computing centres and participating institutions on four continents. A prototype for interactive distributed analysis using the Parallel ROOT Facility (PROOF) and AliEn will be used to analyse the results of the data challenge. The AliEn GRID system has been further developed, hardened, and deployed in more than 30 sites. ALICE Offline is participating actively in the LCG project. A review of the Offline manpower mandated by the LHCC took place in September. The ALICE Offline project strategy to cope with the manpower limitations has been endorsed by the review committee; however, a shortfall of 3–4 people in the Core Offline of ALICE was also identified. The Collaboration is now trying to find the necessary resources.

Installation Activities at Point 2

The overall installation schedule for the ALICE experiment has been rearranged and adapted to the requirement set by the delivery of components and the commissioning of subdetectors. The large central support beams, which will support the central detector complex, have been installed inside the L3 solenoid.

Experimental Physics Division 41 The construction of the new control room for the ALICE experiment has been completed. The experimental area has been cleaned and painted. A temporary foundation for the vertical assembly of the dipole magnet has been constructed inside the experimental area and the vertical assembly of the magnet has started.

The construction of all major support structures is proceeding according to plan. Several support structures have already been delivered to CERN and are undergoing ﬁnal assembly at Point 2. The tendering for the main components of the muon absorber has been completed and most items have been delivered to Point 2. The design work is now concentrating on the assembly and installation procedures. All work on the L3 magnet has been completed and the magnet was successfully powered to its nominal ﬁeld of 0.5 T.

LHCb

The LHCb Collaboration has completed the reoptimization of the detector and submitted a Technical Design Report (TDR) in September. It describes the overall layout of the reoptimized detector as well as the technical design, cost, and construction milestones of the subsystems which were affected by the reoptimization process. The physics performance of the experiment is re-evaluated and the overall cost and schedule are revisited in the document. A TDR for the trigger system was also submitted in September and all the TDRs related to the detector subsystems have now been completed. The only TDR that still needs to be produced is that for computing and is expected in 2005.

The physics performance studies presented in the reoptimization TDR are considerably more realistic than those given in the Technical Proposal. Simulated detector responses have been adjusted to the test beam results and event reconstruction has been performed in the same way as for the real data without referring to any information from the event generation. The performance studies show that the reoptimized detector, together with its trigger, can achieve the physics goals given in the Technical Proposal. Furthermore, the cost of the detector is slightly reduced and the experiment should be ready for physics in 2007.

The layout of the LHCb detector is shown in Fig. LHCb–1 and the magnet under construction is shown in Fig. LHCb–2.

y M4 M5 M3 M2 5 m SPD/PS HCAL Magnet ECAL RICH2 T3 M1 T1T2 RICH1 250mrad

100mrad Vertex TT Locator

5 m 10 m 15 m 20 m z Fig. LHCb–1: LHCb detector.

42 Experimental Physics Division Fig. LHCb–2: LHCb magnet under construction.

Experimental Area

The refurbishing of the underground experimental area, UX85, has been essentially completed. The LHCb dipole magnet is being constructed there, although the area is mainly used by the LHC machine group for the installation of the LHC cryogenic equipment in the tunnel and the assembly of a cryogenic plant in UX85.

The LHCb detector

Magnet

The construction of the yoke is advancing in UX85. The lower half and the two sides have already been ﬁnished. The installation of the coils is under way.

Beam Pipe

The detailed technical design of the beam pipe has been reviewed and the production of the ﬁrst 25-mrad beryllium section has been completed. This section passed all its mechanical and vacuum tests, and thus can be used in the experiment.

VELO

The engineering design of the vacuum tank housing the silicon sensor planes has been completed. While further prototype work and the review process will continue, the design has been accepted by the LHC vacuum group. Following this approval, construction of the vacuum tank has started. Beetle chips based on 0.25 µm CMOS technology are used for the readout by both the VELO and silicon trackers. Intensive tests of the Beetle 1.2 revealed a signiﬁcant number of problems. After correcting the design faults, a new version of the chip, Beetle 1.3, has been produced and is now being tested.

Experimental Physics Division 43 RICH

In October, the Hybrid Photo Diode (HPD) was ﬁnally selected to be the photon detector of the LHCb RICH system. A detailed production schedule is being discussed with all the manufacturers involved and a rigorous plan for the quality control is being worked out. Construction of the RICH2 detector is advancing. The large entrance and exit windows have been manufactured and the assembly of the super structure has started. The construction of the mirror system is advancing. The RICH1 detector has been redesigned as part of the reoptimization. A detailed engineering design is being worked out.

Silicon Tracker

In the reoptimized LHCb detector, the silicon tracker consists of the Inner Tracker (IT) and the Trigger Tracker (TT). After carefully evaluating the results from the beam test with different prototype sensors, the thickness of the sensors has been chosen to be 400 µm for the inner tracker and 500 µm for the trigger tracker. The sensor arrangements are being re-evaluated and detailed engineering designs are in progress. A full chain of the optical data link was assembled and a radiation test of the crucial components was successful.

Outer Tracker

The preparation of the three production centres for the outer tracker is being completed. Final prototypes are being constructed to test the procedure which will be used for the serial production. Based on this experience, further improvements to the production procedure will be implemented. In parallel, ageing studies are continuing. No conclusion has yet been reached on whether to use CF4 in the ﬁnal gas mixture.

Calorimeter System

The production of the electromagnetic calorimeter modules has been completed. More than 30% of the hadron calorimeter modules have been constructed and the serial production of the preshower detector and scintillator pad detector has started. Photomultipliers are being delivered and tested as planned. A Cockcroft– Walton system has been selected for the high-voltage supply system.

Muon System

Preparation of the five production sites for the multiwire proportional chambers is being completed. At two sites, several chambers have been produced using the facilities for the serial production. The quality control procedure is being finalized. In parallel, ageing studies of the chambers are continuing to define the final gas mixture.

Trigger

The Trigger TDR was completed in September. The system is based on the ﬁrst-level hardware trigger (level-0) followed by software trigger levels, level-1 and High Level Trigger (HLT), where the algorithms will run in an online processor farm with ~1500 CPUs. Prototype development for the level-0 hardware modules is advancing well. The level-1 trigger algorithm looks for events where tracks with high transverse momentum and large impact parameter are present. For the high level trigger, all the detector information is available to select events with interesting B meson decays.

44 Experimental Physics Division Computing

Ofﬂine: The LHCb software used for event generation, detector simulation, event reconstruction and physics analysis, is now in a stable production phase. For the reoptimization and trigger TDRs, a total of more than 30 million events were generated and reconstructed using 19 production sites. The resulting data were collected at CERN and used for the analysis work. Progress has been made with the new C++ based simulation application (GAUSS) and digitization application (BOOLE). The LCG (LHC Computing Grid Project) software components are progressively incorporated as they become available. The LHCb software team is also making major contributions to the LCG developments.

Online: The level-1 trigger was integrated into the DAQ system and this involved no major architectural changes. Work has started to adapt the LHCb software framework to the online environment for the level-1 and HLT. Full system tests with existing prototypes for the timing and fast control system show that the performance required by the front-end electronics can be met.

TOTEM

The major achievement of the TOTEM experiment in the year 2003 has been the presentation of the Technical Design Report to the LHC Committee. The document presents all the physics potentialities of the TOTEM detector alone or in conjunction with CMS and describes all the relevant aspects of the hardware and software necessary to perform the experiment.

The measurement of the total cross-section and of the machine luminosity is the ﬁrst objective of the experiment. The total cross-section will be determined with the luminosity-independent method based on the simultaneous measurement of low-momentum-transfer elastic scattering and of the rate of inelastic interactions with fully inclusive trigger. Elastic scattering events will be detected with the ‘Roman Pot’ technique using a suitable machine optics obtained by properly tuning the quadrupoles in the intersection region. The measurement of the total cross-section will be followed in due course by the study of elastic scattering at large momentum transfer and of diffractive processes.

The total cross-section measurement by means of the ‘luminosity-independent’ method is based on the simultaneous detection of elastic scattering at low t (t ~ p2θ2) and of the inelastic interactions.

Elastic Scattering

The elastic proton–proton scattering has to be measured down to the smallest possible t-values (few 10–3 GeV2) to allow an accurate extrapolation to t = 0, i.e. to the ‘optical point’, assuming a simple exponential dependence which is known to describe the data for t < 10–2 GeV2.

A detailed study has been performed to determine the accuracy in the extrapolation to t = 0 taking into account the various effects related to the apparatus and to the machine performances. The result is that, with realistic assumptions, the elastic rate can be measured with a precision of better than 0.5%.

Experimental Physics Division 45 The detectors have to approach the beam as close as possible. In practice this is achieved by placing high- resolution silicon detectors in special movable sections of the beam vacuum chamber known as ‘Roman Pots’. During injection and beam tuning the detectors will be retracted to be moved close to the beam only during stable conditions.

Elastically scattered protons have to be detected at very small emission angles of typically 10 µrad. In ∗ 2003 a new superior beam optic with β = 1540 m has been calculated by a collaboration between TOTEM and the ABP group. The main new feature of this optics is that parallel-to-point focusing can be achieved in both projections at almost the same location, dramatically improving the resolution in the momentum transfer and the azimuthal angle of the scattered protons.

Figure TOTEM–1 shows the position of the Roman Pots along the beam line at 147 m and 220 m. A station at 180 m may be equipped later. At each station two Roman Pots about 4 m apart allow an accurate angle determination, necessary for background reduction. It is important to note that the 147 m Roman Pots are located before the D2 magnet, while the 220 m tracking station is well behind it. This geometry naturally implements a magnetic spectrometer in the standard insertion, permitting TOTEM to measure particle momenta, with an accuracy of a few parts per thousand. This will allow the accurate determination of the momentum loss of quasi-elastically scattered protons in diffractive processes.

Fig. TOTEM–1: The inelastic TOTEM detectors T1 and T2 embedded in the CMS experiment and the Roman Pots at 147 m, 180 m, and 220 m along the LHC beam line.

The large bunch size (0.45 mm) resulting from the high-β optics requires a crossing scheme with zero crossing angle, hence a number of bunches reduced to 43, which is compatible with the LHC injection scheme and is also foreseen for machine development studies.

46 Experimental Physics Division The design of the mechanics of the Roman Pots station has been completed and a prototype has been built. Tests on the technology to implement the very thin window of 0.2 mm have demonstrated the feasibility of the option chosen.

Roman Pot Detectors

The experiment needs detectors which are fully efﬁcient very close to the physical edge of the detector itself. In other words, the detector has to be edgeless on one side (the side facing the beam). This is a really special requirement of the experiment.

The sensitive area of the detectors inside the pots is ~3 × 3 cm2. The required spatial resolution is ~20 µm to match the physics requirements and the properties of the beam optics.

Two innovative silicon detectors technologies have been tested with good results in the beam during the year 2003:

– Planar silicon strip detectors (1 × 1 cm2) with two (miniaturized) current terminated guard rings could be operated at room temperature.

– 3D detectors with an area of about 10 mm2 exhibit a dead zone of at most a few microns and could easily be operated.

Planar Silicon Detector

The conceptual idea of the new approach is to allow the full detector bias to be applied across the detector chip cut, and to collect the resulting current on an implanted ring, which surrounds the active area and is biased at the same potential as the detecting strips.

The ﬁrst sample of detectors based on this principle and with different design parameters has been been developed with a joint effort between the TOTEM group at CERN and Megaimpulse, a spin-off company from the Ioffe PT Institute in St Petersburg (Russia). These detectors were successfully tested in the X5 beam at CERN in September 2003.

The detectors were read out with the APV chip from CMS which is the electronics that will be ﬁnally used by TOTEM. Data were taken to study simultaneously the edges of two different modules at a ﬁxed distance overlapped by a third reference detector. The 300 µm thick detectors operated at room temperature with a S/N = 20.

A sharp decrease of the efﬁciency close to the cut detectors’ edge is observed on both sides. The end of the strips at the cut edge of each detector was measured with micrometric precision (10 µm) with respect to the 50 µm strip of the corresponding reference detector. The position of the sensitive edges can be determined with high precision from the distributions of the tracks. We estimate a combined statistical and systematic error of 20 µm. Since the strips start at 40 and 50 µm away from the physical edge respectively, the detectors exibit an insensitive edge region of 60–70 µm.

Experimental Physics Division 47 3D Silicon Detectors

S. Parker proposed 3D detectors in 1995 and C. Kenney ‘active edges’ in 1997. This technology, which combines micro-machining and standard VLSI (Very Large Scale Integration) processing, takes full advantage of the development of high-precision etching techniques in silicon. 3D and planar-3D detectors, both provided with active edges, have been fabricated at the Stanford Nanofabrication Facility (SNF), USA.

In 2003 these were tested with X-rays at the Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory, Berkeley, California, and with the X5 high-energy particle beam at the CERN SPS. The aim of the high-energy test beam experiment was to test the operation and edgelessness of 3D detectors in a high-energy particle beam. The system efﬁciency was measured with reference to a silicon microstrip beam telescope. The 3D devices under study had a dimension of 3.195 × 3.948 mm2. The thickness was 180 µm. Three of these detectors were bonded to ATLAS SCTA128VG readout electronics chips developed for the ATLAS SCT silicon tracker.

Using the telescope predictions for both track projections, two-dimensional efficiency maps of the 3D detectors were obtained. The data demonstrate that the sensor width, known from the photolithography process, is reproduced by the efficiency curve within two statistical standard deviations, which confirms the ‘edgeless’ nature of the 3D detector technology. This property is further underlined by the steep efficiency rise from 10% to 90% within only (18±7) µm on average.

Final-sized detector prototypes are under construction for a test in the beam in 2004.

Trigger

The trigger of the leading proton detector in the Roman Pot is obtained with the VFAT chip developed by the MIC group. This allows the extraction from the detectors installed in the Roman Pots of a fast-OR signal in time to be used for trigger selection within the CMS latency.

A prototype of this newly developed chip exists and will be tested together with ﬁnal-sized silicon prototypes in the test beam foreseen for the summer of 2004.

Inelastic Detectors

The measurement of the total inelastic rate is performed with telescopes in the forward region covering between 3.1 and 6.8 in η. The telescopes will trigger on minimum-bias events and will have a tracking capability sufﬁcient to reconstruct the interaction vertex in such a way as to discriminate between interactions and background events (beam halo, beam gas, or interaction in the vacuum chamber).

The measurement of the inelastic rate requires a trigger as inclusive as possible and a clear discrimination of beam–beam events from background interactions. The telescopes allow the following triggers to be used:

– double-arm trigger, which detects more than 99% of non-diffractive events;

– single-arm trigger, which detects the events escaping the double-arm trigger, mostly diffractive interactions with all visible tracks in one arm only.

48 Experimental Physics Division The trigger signals will be compatible with the CMS triggering scheme to allow common runs for luminosity calibration and diffractive physics measurements to take place.

Detailed Monte Carlo simulation of the different processes to be measured by the inelastic telescopes has shown that the loss of single diffractive events is mainly due to events with a very low mass M, where all the particles have pseudo-rapidity above 7 and hence escape detection by the telescopes.

To obtain the total inelastic rate, the fraction of events escaping detection due to the incomplete angular coverage can be estimated by extrapolation. In the case of single diffraction, the reconstructed 1/M2 distribution has been linearly ﬁtted for M > 10 GeV and the extrapolation to low masses have then been compared with the Monte Carlo. For single diffraction, the extrapolated number of events differs from the Monte Carlo by 4% corresponding to a 0.6 mb uncertainty on the total cross-section. The same estimate for the double-diffraction and double-Pomeron exchange gives 0.1 mb and 0.02 mb of uncertainties, respectively.

The uncertainty on the inelastic cross-section has been estimated to be 0.78 mb.

Combining the uncertainty from the elastic and inelastic rate gives an overall uncertainty on the measurement of the total cross-section of ~1%.

The telescope to trigger and partially reconstruct the inelastic events will be placed in the forward region of CMS (see Fig. TOTEM–1). In order to cover a sufﬁcient range in rapidity, it will be split into two telescopes:

– T1 ( 3.1 < η < 4.7) will be installed in the end-cap of CMS in a detector-free region between the vacuum chamber and the iron of the magnet on each side. The region reserved for TOTEM is between 7.5 m and 10.5 m from the IP.

– T2 (5.3 < η < 6.7) will be installed in the forward shielding of CMS between the vacuum chamber and the inner shielding of the HF calorimeter, in front of the newly proposed CMS CASTOR calorimeter, at a distance of 13.5 m from the IP.

T1 Telescopes

Each detector plane of T1 is composed of six overlapping detectors to obtain a full azimuthal coverage. The solution proposed also makes it possible to obtain an overlap of the sensitive region between the two halves of the telescope. The telescope consists of ﬁve planes of Cathode Strip Chamber (CSC) detectors distributed over a distance of 2–5 m to trigger and properly track the traversing particles and to reconstruct the vertex of the interaction. The trigger of the telescope will be built from the anode signals using CMS-like electronics.

In 2003 three full-sized CSC detectors were built and tested in X5 demonstrating that the foreseen trigger scheme will be effective up to a bunch separation of 75 ns. The measurement of the gain and precision of the detectors reproduced what is required by the experiment.

A solution for an easy installation in CMS which fulﬁls all the requirements and can be accomplished in the short time available has been found and discussed in detail with CMS.

Experimental Physics Division 49 T2 Telescopes

Two possible technologies have been studied for T2.

A solution using for tracking the same silicon microstrips detectors designed by CMS for the Tracker Outer Barrel has been studied: most of the technical details of the detectors are fully understood from the CMS development. Each T2 telescope will be made of ﬁve silicon detector planes. Eight silicon detectors are overlapped to form either a tracking or a trigger plane. Two single-sided detectors are mounted orthogonally back to back to obtain a two-coordinate measurement in the plane. The readout will be either with the APV for tracking or the VFAT chip for trigger.

A new option considered is to use triple Gas Electron Multiplier (GEM) detectors with pad and strip readout. The GEM is a detector which has already been employed in various experiments (HERA-B and COMPASS). It combines good spatial resolution with very high rate capability and a good radiation tolerance.

The detector’s sensitive area can be tailored into the shapes required by the experiment. This ﬁts nicely with the TOTEM need for a detector to be installed around a small-diameter vacuum chamber. Eight planes are envisaged for this option. Two identical detectors are needed to complete a measuring plane.

The technology to build the readout board is such as to extract simultaneously the two-coordinate information of the position of the ionization deposit in the detector. The conﬁguration of the board will allow a precise reconstruction of the traversing particle position in the radial direction (the coordinate useful for vertex reconstruction) using analog information by strips with 400 µm pitch. The surface of the board will then be subdivided in pads of varying size to cover the same ∆θ and ∆ϕ and read out by the trigger chip VFAT. The pads will provide information for trigger and pattern recognition.

The design of a GEM prototype to be fabricated and tested in 2004 is well under way.

Besides the very precise measurement of the total cross-section and the elastic scattering performed using only TOTEM detectors, the integration of TOTEM into the general-purpose detector CMS offers the prospect of more detailed studies of diffractive events. The TOTEM triggers, combining information from the inelastic detectors and the silicon detectors in the Roman Pots 220 m upstream, can be incorporated into the general CMS trigger scheme, thus allowing them to be combined with other CMS triggers.

The CMS experiment extended by the TOTEM detectors into the very forward region and the Roman Pot detectors along the LHC beam line will be the largest acceptance detector ever implemented at a hadron collider.

50 Experimental Physics Division The SPS Fixed-Target Programme

NA48/1

Rare kaon decays offer a broad window of opportunity to test the Standard Model of particle physics. Of particular interest are those decays mediated by Flavour Changing Neutral Currents (FCNCs) that are highly suppressed in the Standard Model because they can proceed only via quantum loops. These studies are complementary to those performed in B decays. Results are typically displayed in terms of unitarity relations (triangles) in the complex plane. The relevant kaon decays are depicted in Fig. NA48/1–1.

(ρ,η) → π0νν– α K+ → π+νν– KL K → π0e+e– S η → π0 + – → π0γγ KL e e KL K → eeγγ L γ β (0,0)(1,0) (1.4,0) ρ

K → γγ, K → e+e–γ K → µ+µ– L L L → + – + – + –µ+µ– KL e e e e , e e Fig. NA48/1–1: The rare kaon decays related to the study of the unitarity triangle.

→ π0 + – The highlight of the NA48/1 activities during 2003 was the ﬁrst observation of the rare decay KS e e . The physics interest is to measure the long distance contribution that generates CP violation from mixing in → π0 + – λ KL e e and, if not well measured, prevents the extraction of Im t, the relevant Cabibbo–Kobayashi– Maskawa (CKM) matrix element. A rectangular signal region (2.5 standard deviations in M(γγ) and M(e+e–γγ) resolution) and a rectangular control region of 6 times 6 standard deviations, both centred around the kaon and π0 mass, were kept masked until the background studies were completed in order to avoid any human bias. A comparison between the NA48/1 data and the Monte Carlo simulation is shown in Fig. NA48/1–2 for the 2 2 events satisfying the relation: 0.09 GeV/c < Mee < 0.165 GeV/c . These events have the same topology as the signal but fall outside the masked search region and can be used to check the reconstruction procedure. The data is well described by the simulation (the normalization is absolute). One can notice that the π0 → e+e– (BR ≈ 6 × 10–8) contribution is quite visible and gives an idea of how small the residual backgrounds due to π0 Dalitz decays and conversions are. This is due, to a large extent, to the very good energy resolution of the detector, a liquid krypton electromagnetic calorimeter.

No events reconstructed with two electrons of the same sign were found in the corresponding signal → π0 region. This demonstrates that KS 2 events in which one pion Dalitz decays and a photon converts with subsequent loss of two charged particles of opposite sign are not of concern. The radiative background due to → + –γγ KL,S e e was measured analysing data collected by NA48 in 2001 from a pure KL beam. The data set contains ten times more K → e+e–γγ events than the 2002 sample and a precise measurement of the radiative background can therefore be made. Background from the accidental overlap of different kaon decays has also → π ν to be taken into account. It typically originates from the time overlap of a KL e decay where the pion is → π0π0 π0 misidentiﬁed as an electron with a KS decay where one is lost outside the acceptance. Given the

Experimental Physics Division 51 very good time resolution of the detectors and the wide readout window, this background is measured by counting the events that pass the analysis in the time side-bands and extrapolating the result in the signal region. The summary of the expected backgrounds is reported in Table NA48/1–1.

→ π0 + – Table NA48/1–1: Sum of the backgrounds to KS e e

Source Control region Signal region →ππ00 KSDD 0.03 < 0.01 → + –γγ KS e e 0.11 0.08 Accidentals 0.19 0.07 Total 0.33 0.15

Many other sources of background, for example those originating from neutral cascade decays, were investigated and found to be negligible. The inspection of the control box surrounding the signal region revealed no events, which is consistent with an expected background of 0.33 events. In the signal box seven candidate events were found. The candidates are displayed in Fig. NA48/1–3.

90 0.65 2002 data 80 0.5 π0π0 > D (mee 0.09 GeV) 0.6 70 0.49 π0π0 + conversions 0.134 0.136

60 ) 0.55 π0π0 2 D + conversion kevlar 50 π0π0 + conversion DCH1H1 0.5

D (GeV/c

40 γγ ee No. events π0π0 (ee) m 30 0.45 π0π 0 DD 20 0.4 10

0 0.35 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 2 2 mee (GeV/c ) mγγ (GeV/c )

γγ γγ Fig. NA48/1–2: The Mee invariant mass Fig. NA48/1–3: The M(ee ) vs. M( ) distributions for events that satisfy a ±2.5σ cut distribution for the seven candidate events. The

on Meeγγ around the kaon mass. same events are shown in the inset in more detail.

52 Experimental Physics Division Given the background expectation of 0.15 events, the probability that all seven events are background is ≈ –10 → π0 + negligibly small ( 10 ). The events are therefore interpreted as the first observation of the KS e e ππ00 decay. The flux, measured counting D events which are collected by the same trigger, amounts to × 10 3.51 10 KS decays. After correcting for the acceptance and dividing by the flux the measured branching ratio for M(ee) > 0.165 GeV/c2 is found to be:

→>π02+− =±+−15. × 9 BR() KS e e,(). M ee0165 GeV /c () 30 .−12. ( stat ) 02 .() syst 10 .

Assuming a vector interaction and unity form factor, the result extrapolated to the full phase space becomes:

→ π0 +− =±+−28. × 9 BR() KS e e()58.().()−23. stat 08 syst 10 , where the systematic error is totally dominated by the form factor uncertainty. This measurement can be related to the parameter:

=±+026. as 106..−021. 007.

λ The sensitivity of the total CP-violating branching ratio as a function of Im t is shown in Fig. NA48/1–4 for the two signs of aS. If the interference is constructive, as preferred theoretically, the observation of the → π0 + – decay KL e e could be within the reach of possible future, neutral, rare kaon experiments.

10 λ Global fit for Im t

8 aS = –1.06 ) 11 – (10 6 CPV ) – e + e 0 4 → π L aS = +1.06 BR(K 2

0 01234 λ –4 Im t (10 ) → π0 + – Fig. NA48/1–4: The sensitivity of the total CP-violating KL e e branching λ ratio as a function of Im t for the two signs of the interference term.

Experimental Physics Division 53 NA48/2

A high-precision study of charged kaon decays is in progress at the SPS using a novel design for simultaneous K+/K– beams and an upgraded NA48 set-up. The main goal is to search for CP violation in K± → π+π–π± decays. The experiment is designed to reach a sensitivity, limited by statistics rather than –4 + – + – systematics, of ~10 in the measurement of the direct CP-violating asymmetry Ag = (g – g )/(g + g ), where g+ and g– are the slope parameters describing, respectively, the linear dependence of the K+ and K– ∗ decay probabilities on the u kinematic variable of the Dalitz plots. The u variable is related to the energy ()Eπ of the odd pion (the pion having the sign opposite to that of the decaying kaon) in the kaon centre-of-mass 2 ⋅ ∗ system as follows: u = (2MK/m ) (MK/3 – Eπ ), where MK and m are the kaon and pion mass, respectively.

In order to achieve the required sensitivity, in addition to the capability of withstanding high rates, the experiment has to be carried out according to a strategy which ensures the highest possible immunity to detector asymmetries and perturbations. The approach followed consists in considering only slopes of ratios of u distributions which, alone or in suitable combinations that assure automatic compensation, can be distorted only by the simultaneous presence of time instability between data samples and Right–Left asymmetry in the detector acceptance.

Exploiting the high detection efﬁciency and precision in energy measurement for photons of the NA48 0 ± → π0π0π± Liquid Krypton calorimeter (LKr), the corresponding asymmetry Ag in K decays will also be measured, with a sensitivity again limited by statistics.

± At the same time, semileptonic decays of K can be studied in order to measure the Vus element of the CKM matrix with better precision than currently available.

6 π π 0 High statistics (~10 ) of Ke4 decays can be analysed, allowing the – scattering length parameter a0 to be measured with an accuracy of better than 1 × 10–2. This permits the size of the qq condensate of the QCD vacuum postulated in χPT to be measured.

± ± The present knowledge of several rare decays of the charged kaon such as: K → e±ν(ν), K → π±π0γ, ± ± ± ± K → π±π0γγ, K → π±π0l+l–, K → π±l+l–, K → l±νl+l–, and others, can be extended as well. This will allow in particular χPT predictions at next-to-leading order to be tested.

The NA48/2 experiment was commissioned and the beam line, detector, and triggers properly tuned during the ﬁrst weeks of beam operation in 2003.

As mentioned above, the new K12 beam line was designed and built to transport simultaneously positive and negative particles with central momentum 60 GeV/c to the upgraded NA48/2 detector in the ECN3 underground hall at the SPS.

The charged particles are produced in the target station T10 in TCC8 by 400 GeV/c primary protons – transported via the P42 beam line – at a chosen nominal intensity of 7 × 1011 ppp on target (with 16.8 s cycle time and 4.8 s ﬂat-top) (Fig. NA48/2–1).

54 Experimental Physics Division SIMULTANEOUS K+ AND K– BEAMS Final TAX 17 TAX 18 FD FD collimator Defining Protecting – K collimators collimator Magnet Cleaning collimator Decay volume NA48 K– KABES 1 KABES 3

0.36 MUV Target mrad Hodoscopes Calorimeters K+ KABES 2 DCH1 DCH4 K+ He tank D F D F Vacuum tank + Quadrupole 2nd Spectrometer FRONTEND ACHROMAT Quadruplet ACHROMAT Fig. NA48/2–1: Schematic vertical section of the simultaneous K+ and K– beam line (not to scale). Outside the dipole magnets the lower and upper envelopes, respectively, of the K+ and K– beams are shown. Their axes are steered to coincide to a precision of ≤ 0.3 mm.

The positive beam flux at the exit of the final collimator is estimated to be 3.8 × 107 particles per pulse (of which 2.2 × 106 are K+); the negative beam flux is 2.6 × 107 ppp (1.3 × 106 K–). The corresponding fluxes of positive and negative muons from K and π decays in the 114 m decay volume are 1.1 × 106 and 0.8 × 106 per pulse, respectively. Using a series of magnetized-iron sweeping elements around the beam line upstream of the final collimator, the total flux of muons crossing the area (~5 m2) of the detector around the central beam tube is limited to ~1.5 × 106 per pulse.

A new beam detector, KABES, was integrated into the beam line to provide particle-by-particle momentum and position measurement. KABES is a TPC-type detector using MICROMEGAS with an ampliﬁcation gap of 50 µm.

The peak rate on the strips located in the centre of the beam was measured to be ~2 MHz.

Spatial resolutions of ~100 µm have been achieved in the horizontal drift direction and of ~130 µm in the vertical direction using the strips. A time resolution of 0.65 ns has been measured.

The data accumulated in the 2003 run corresponds to only a part (~50%) of the planned statistics for the measurement of the direct CP-violating asymmetry in charged-kaon decays.

A preliminary express analysis of a part of the data accumulated shows that the estimated statistical precision and systematic uncertainties of the measured asymmetry Ag are in agreement with those indicated in the proposal. More details can be found elsewhere. The experiment will continue data taking in 2004.

Experimental Physics Division 55 NA49

The NA49 experiment (NIKHEF Amsterdam, Univ. Athens, Comenius Univ. Bratislava, KFKI Budapest, CERN, INP Cracow, GSI Darmstadt, JINR Dubna, IKF Frankfurt, IP Kielce, Univ. Marburg, MIT, MPI Munich, IPNP Prague, INPNE Sofia, Univ. Sofia, INS Warsaw, Univ. Warsaw, Univ. Washington Seattle, RBI Zagreb) investigates hadron production in p+p, p+A, and A+A collisions at the SPS. Its high-precision tracking and particle identification in a wide acceptance allows for a unique study of soft hadronic phenomena ranging from the most elementary hadronic interactions over impact parameter controlled p+A collisions to heavy-ion interactions with different masses and energies.

The experimental set-up comprises mainly two medium-sized TPCs (VTPC-1,2 with 3 m3 each) located inside two superconducting vertex magnets, a small TPC (G-TPC) positioned between the two VTPCs on the beam and filling the acceptance gap due to the insensitive region of the VTPCs around the beam, and two large-volume TPCs (MTPC-R,L with 20 m3 each) positioned downstream of the vertex magnets symmetrically to the beam for tracking and particle identification via dE/dx. Highly segmented scintillator TOF arrays complement particle identification. Calorimeters for transverse-energy determination and triggering, a detector for centrality selection in p+A collisions, beam definition detectors and two Veto- Proportional-Chambers (VPCs) for detection of neutrons in connection with one of the calorimeters complete the set-up.

In 2003 a lead glass detector was added to the set-up and successfully tested. It is positioned 5 m downstream of MTPC-R, consists of 192 modules recuperated from the OPAL detector, and covers a surface of 150 × 110 cm2. The aim of the test run was to determine the design parameters of a new detector to be built for a possible new physics programme with the NA49 detector.

Data analysis is continuing and the CERN group concentrated its activities on the study of the consequences of isospin symmetry on the behaviour of certain observables especially investigated in heavy- π+ π– + – ion collisions. To this intent the pT distributions at ﬁxed values of xF were determined for , and K , K produced in p+p and n+p interactions. Typical distributions are shown in Fig. NA49–1a. One observes that the π+ π– pT distributions of and change position when going from a proton to a neutron projectile, i.e., the distribution of π– produced in n+p interactions corresponds to the distribution of π+ produced in p+p collisions + – and vice versa. On the other hand, the pT distributions of K and K stay ﬁxed and do not depend on the projectile particle. This must of course have immediate consequences on the K+/π+ ratio in heavy-ion collisions as they are dominated by neutron fragmentation modulated with a threshold cut-off for strangeness production. In fact, the K+/π+ ratio is claimed to show an interesting non-monotonic behaviour as a function of sqrt(s) in central Pb+Pb collisions. But it turns out that knowing that the π+ production in p+p interactions corresponds to the π– production in n+p collisions, and knowing the proton and neutron content of the Pb + π+ nucleus (fp = 0.4 and fn = 0.6, respectively), the sqrt(s) dependence of the K / ratio in Pb+Pb collisions can be deduced experimentally from the sqrt(s) dependence of the π+/π– and K+/π+ ratios measured in p+p interactions via the formula

+ π+ + π+ ⋅ π+ π– π+ π– (K / )AA = (K / )pp ( / )pp/(fn + fp ( / )pp) .

The curve shown in Fig. NA49–1b represents a compilation of p+p data on the π+/π– ratio measured at various energies and the dashed curve in Fig. NA49–1c is achieved with the above formula using a parametrization of the K+/π+ data measured in p+p at various energies as displayed in the same ﬁgure. It

56 Experimental Physics Division becomes evident that the non-monotonic behaviour in the sqrt(s) dependence of the K+/π+ ratio observed in central heavy-ion collisions is indeed to be expected from the underlying elementary interactions.

3 a) b) 158 GeV/c π+ in p+p 158 GeV/c 10 π+ in n+p 2.5 π– in p+p π+/π– in p+p –

– π 2 π in n+p / +

π xF = 0 x = 0.2 F 1.5 1 1

+ 0.12 K in p+p c) K+ in n+p 0.1 K– in p+p 0.08 0.1 K– in n+p + π /

+ 0.06

x = 0.1 K F K+/π+ in p+p 0.04 x = 0 0.02 F 0.01 0 0 0.2 0.4 0.6 0.8 1 010203040506070 pT [GeV/c] sqrt(s) [GeV] π+ π– + – Fig. NA49–1: a) pT distributions of , and K ,K produced in p+p and n+p interactions at 158 GeV/c; b) compilation of data on π+/π– ratio measured in p+p interactions at various energies; c) data on K+/p+ ratio measured in p+p collisions as a function of sqrt(s) together with a parametrization of these data (solid curve) and a prediction of this ratio for central Pb+Pb collisions (dashed curve) assuming 40% protons and 60% neutrons in a Pb nucleus.

NA50

The NA50 Collaboration (Alessandria, Annecy, Aubière, Bucharest, Cagliari, CERN, Lisbon, Moscow, Orsay, Palaiseau, Torino, Villeurbanne, Yerevan) collected its last samples of Pb–Pb and p–A data in 2000 at the CERN SPS. The aim of the experiment, which started in 1994, has been to study heavy-ion interactions and, in particular, J/ψ production, considered since 1986 as a potential signature for the transition of normal nuclear matter to the predicted Quark Gluon Plasma state.

The last Pb–Pb data collection was made with an improved trigger system and with a single thin target kept in a vacuum container which avoided lead–air interaction background and any ambiguity in the origin of the interaction. The study of J/ψ production could thus be extended down to very peripheral Pb–Pb interactions.

The new p–A data, together with two other sets collected with different beam-target conditions, in particular different beam intensities and incident momentum, provided the necessary basis to minimize systematic effects and study J/ψ normal production in proton-induced reactions. The study of lighter systems like p–A, and S–U interactions and their comparison with Pb–Pb collisions is a must in order to experimentally establish that, in the latter case, an abnormal behaviour is indeed observed.

Experimental Physics Division 57 The year 2003 was fully devoted to data analysis, with improved versions of the analysis programs together with homogeneous data selection and analysis procedures for the various data sets. This effort was extended to the reanalysis of J/ψ production in sulphur–uranium interactions from data collected by the NA38 Collaboration more than 10 years ago.

The p–A data samples were analysed separately in the framework of the Glauber model taking into account the production of the charmonium state and its absorption in nuclear matter. The absorption cross- section deduced from these data and, separately, from S–U interactions exhibit good compatibility so that there is no experimental evidence of suppression mechanisms appearing speciﬁcally in S–U interactions and different from those already present in proton–nucleus collisions. From a simultaneous ﬁt on all the p–A and S–U reanalysed data, the normal absorption cross-section of J/ψ in nuclear matter can be determined, leading to:

σabs =± J/ ψ ()43.. 03 mb .

The comparison of the measured J/ψ production cross-section per nucleon–nucleon collision (or, equivalently, normalized by the corresponding Drell–Yan cross-section) with the expected values as deduced from the measurements in proton and sulphur-induced collisions is displayed in Fig. NA50–1 as a function of L, the mean path of nuclear matter seen by the cc pair, a useful centrality estimator for ion–ion collisions. It shows that while peripheral Pb–Pb interactions follow the normal nuclear absorption behaviour, accurately determined from the analysis of our p–A data, there is, for mid-central interactions, a departure from this normal absorption which is followed by a steady decrease of the J/ψ yield with increasing centrality.

1.8 ψ J/ / DY4.2-7.0 Pb-P b 1.6 S-U p-A 1.4

1.2

0.8

0.6 Measured / Expected

0.4 ψ′ / DY4.2-7.0 Pb-P b 0.2 S-U p-A 0 0246810 L (fm) Fig. NA50–1: Charmonium production cross-section, normalized by the Drell– Yan cross-section, as a function of L, the mean path of nuclear matter seen by the cc pair. The measured values are divided by the ‘expected values’ as deduced from proton and sulphur-induced reactions for J/ψ and from proton-induced reactions only for ψ′.

58 Experimental Physics Division A complete study of ψ′ production has also been performed. The results show a signiﬁcantly different behaviour between proton- and ion-induced reactions with a much stronger absorption cross-section in ion collisions. They also show a very similar suppression, as a function of L, between sulphur- and Pb-induced reactions. The normal absorption cross-section, as determined from p–A reactions only, amounts to:

abs σψ′ =±()79.. 06 mb and is already signiﬁcantly higher than measured for the J/ψ. A comparison of the measured and expected values of the ψ′ production cross-section, is also displayed on the ﬁgure and allows one to compare the J/ψ and ψ′ different behaviours.

NA57

The NA57 Collaboration (Athens, Bari, Bergen, Birmingham, Bratislava, Catania, CERN, Kosice, Legnaro, Oslo, Padua, Prague, Rome, Salerno, St Petersburg, Strasbourg and Utrecht) studies the production of strange and multistrange particles in ultrarelativistic nucleus–nucleus collisions at the SPS.

As ﬁrst observed by experiment WA97, while the yields per nucleon participating in the collision of strange baryons and antibaryons have similar values in p–Be and p–Pb collisions, in Pb–Pb collisions they are instead all clearly above the p–A values. The effect is larger for particles of higher strangeness content, up to a factor about 20 for the |s| = 3 (Ω– + Ω+). Such a behaviour was predicted long ago (Rafelski and Müller, 1982) as a possible signature of the deconﬁnement phase transition from standard hadronic matter to a plasma of quarks and gluons. Microscopic hadronic collision models do not reproduce these data. Hyperon enhancements are one of the main pieces of evidence for the creation in Pb–Pb collisions at the SPS of a new state of matter presenting many of the expected features of the Quark Gluon Plasma.

NA57 is designed to investigate the origin of this enhancement by measuring the variations of the effect as a function of the energy and centrality (i.e. number of participants) of the nucleus–nucleus collisions. The apparatus consists of a telescope of silicon pixel detectors (about 1.1 M channels) and silicon microstrip detectors, and of a set of multiplicity detectors. Pb–Pb data have been collected at both 160 and 40 A GeV/c. Reference p–Be data at 40 GeV/c have also been recorded. WA97 p–Be and p–Pb data are used as reference for the 160 A GeV/c samples.

In the course of the year 2003 the determination of the energy and centrality dependence of the hyperon enhancement factors was almost completed. In particular, we extracted:

– the centrality dependence of the 40 A GeV/c Pb–Pb mid-rapidity yields of Λ, Ξ–,Ω– (and antiparticles),

– the 40 GeV p–Be mid-rapidity yields of Λ, Λ, and Ξ–, necessary for the determination of the Pb–Pb vs p–Be enhancements,

– the centrality dependence of the 160 A GeV/c Pb–Pb mid-rapidity yields for Ξ– and Ξ+ on the full statistics sample.

Experimental Physics Division 59 Hyperon production is found to be enhanced also at 40 GeV. As at 160 GeV, the 40 GeV enhancements are found to increase with centrality. However, the centrality dependence is steeper. For the most central events, the enhancement is larger at 40 GeV than at 160 GeV. Quantitatively, the increase of the enhancements is less than predicted by statistical canonical model calculations, suggesting that perhaps at 40 GeV the canonical suppression is not yet completely removed.

NA58

COMPASS is a ﬁxed-target experiment investigating hadron structure. It is set up on the M2 beam line of the SPS which can deliver both high-energy muon and hadron beams. About 250 physicists from 26 institutes participate in the experiment. A 60 m long, two-stage magnetic spectrometer is used to track particles produced at the target and to determine the particle type. The main objective for the programme with muons is the determination of the gluon polarization ∆G/G in the nucleon.

The distribution of gluons inside the nucleon can be probed by the Photon Gluon Fusion (PGF) reaction, ∗ γ g → qq. Experimentally, one has to measure the double-spin asymmetry for PGF in the scattering of polarized muons on polarized nucleons. In the case where a cc charm quark pair is produced, the PGF is identiﬁed by detecting the D meson which results from the hadronization of the c quark. In the case of a light qq quark pair, the PGF is identiﬁed by selecting a pair of hadrons with large transverse momenta, pT, produced by the hadronization of the qq pair.

The principal achievements in 2003 are a successful data taking with the 160 GeV polarized muon beam of 2 × 108 muons per SPS spill and the ‘initial layout’ spectrometer set-up, and a full processing and a subsequent analysis of the 2002 data out of which first physics results have emerged including two highlights: the first significant observation for COMPASS of the PGF reaction via the production of D0 mesons, and a measurement of the longitudinal spin asymmetry in the yield of high-pT hadron pairs.

In 2003, out of the ~92 days of SPS beam alloted, about one-third was unfortunately lost due to major incidents in the SPS North Area beam transfer system. During the remaining available beam time, data were recorded with the 6LiD target material polarized successively in the Longitudinal (L) and the Transverse (T) direction with respect to the incoming beam with a sharing of time of 77.5% for L and 22.5% for T.

ε The global data-taking efficiency can be roughly described by the product of two factors: BEAM ε (efficiency of beam delivery) and SPECTRO (spectrometer availability for physics data taking). In 2003, we ε ε ε ε obtained BEAM = 0.63 and SPECTRO = 0.83 compared to BEAM = 0.89 and SPECTRO = 0.76 in 2002, which shows degraded beam performances but an improved spectrometer efficiency. Finally, thanks to constant ε improvements during the run, we could reach values of SPECTRO above 95% during the last two weeks of running where the 5% loss includes mandatory calibrations and alignments.

The various pieces of equipment which provide altogether the tracking of beam particles, the tracking of scattered particles both near and away from the beam, the muon identiﬁcation, and the hadron and electromagnetic calorimetry have performed very well. The stability and the performances of the complex RICH detector, required to identify K and π, have improved considerably.

60 Experimental Physics Division The Polarized Target had excellent performances as in 2002. However, we still do not have the large bore radius COMPASS superconducting solenoid magnet, therefore the SMC magnet of somewhat reduced acceptance had to be used.

The performances of the triggering system have signiﬁcantly improved from 2002 to 2003. The COMPASS Data Acquisition System that handles the read out of more than 200 k electronic channels operated reliably. An additional online ﬁltering system that could help in reducing the huge volume of data (260 Tbytes in 2003) was successfully tested.

Data analysis has made significant progress. Figure NA58–1 shows for the 2002 data the resonance peak for the D0 mesons identified by their two-body hadronic decay D0 → Kπ. The large combinatorial background coming from the other inelastic interactions of quasi-real photons has been significantly reduced by tagging ∗ the D decay into D0 + π and also rejecting collinear decays. This first step towards the extraction of the spin asymmetry for this channel is a very important one.

350

300

250

200

150

100

50 Preliminary 0 –400 –300 –200 –100 0 100 200 300 400

MKπ–MD0 (MeV) Fig. NA58–1: Invariant mass of the Kπ system coming from the D0 decay, as ∗ obtained from 2002 data. This peak is obtained by tagging the D decay and applying kinematical cuts to reduce combinatorial background.

From the 2002 data, the preliminary gamma–deuteron asymmetry for high-pT hadron pairs with longitudinal target polarization is:

γ → ′ A d hh = –0.065 ± 0.036(stat) ± 0.010(syst) .

This channel provides a higher statistics, compared to the D0 channel. However, backgrounds from processes like γ∗q → q and γ∗q → qg compete with PGF, and their contributions have to be removed, which may result in non-negligible additional systematic errors. The next step, which involves a Monte Carlo

Experimental Physics Division 61 simulation to calculate and subtract backgrounds, should lead to the ﬁrst estimate of ∆G/G from this asymmetry. It should be noted that for the PGF process, a positive gluon polarization results in a negative asymmetry.

The analysis of data obtained with transverse polarization is well advanced and results are expected soon for the Collins asymmetry at several values of the xBjorken variable.

More physics results have been derived from the 2002 data. They concern the production of ρ0 and φ vector mesons at low Q2, the measurement of polarization of Λ and Λ, and the ﬂavour decomposition of polarized parton distribution functions using semi-inclusive events. As an illustration, Fig. NA58–2 shows the very large statistics available for the study of the angular distributions for production and decay of ρ0 mesons. Provided a precise modelling of the spectrometer acceptance is obtained, a high-precision measurement of spin density matrix elements will be achieved. It will allow us to address important physics issues, like the s-channel helicity conservation.

=0.125 =0.405 =1.06 =3.31 θ 0.8 0.8 0.8 0.8

0.6 0.6 0.6 0.6

. 0.4 0.4 0.4 0.4

0.2 0.2 0.2 0.2

0 0 0 0 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 cos(θ) cos(θ) cos(θ) cos(θ)

=0.125 =0.405 =1.06 =3.31 0.3 0.3 0.3 0.3 ψ

. 0.2 0.2 0.2 0.2

1/N dN/d0.1 1/N dN/dcos 0.1 0.1 0.1

0 PRELIMINARY0 0 0 01234560/2≠≠3≠/2 2≠ 01234560/2≠≠3≠/2 2≠ 01234560/2≠≠3≠/2 2≠ 01234560/2≠≠3≠/2 2≠ ψ [rad] ψ [rad] ψ [rad] ψ [rad] Fig. NA58–2: ρ0 decay angular distributions for different Q2 intervals. θ is the polar angle of π+ in the rest frame of ρ0. ψ = φ – Φ, where Φ is the angle between the scattering and production planes and φ the angle between the production and the decay planes.

COMPASS has demonstrated the capability to detect open charm from the scattering of high-energy polarized muons on a polarized target and has produced results for spin asymmetries. 2004 will be a full year of data taking before the scheduled shutdown of CERN accelerators in 2005. Data taking will resume in 2006 and plans until 2010 are being worked out by the Collaboration to pursue the completion of the spectrometer beyond the ‘initial Lay-out’ and to carry out the full physics programme.

62 Experimental Physics Division NA60

In the year 2000, 14 years after the start of CERN’s heavy-ion physics programme and when RHIC started data taking at BNL, at much higher colliding energies, it seemed natural to close down the SPS heavy-ion experiments. Nevertheless, a new experiment, NA60, was exceptionally approved in that year, in spite of the financial constraints imposed by the construction of the LHC. This new experiment was different from the previous ones in a fundamental way: rather than being an exploratory experiment, looking for whatever new phenomena could appear when approaching a new frontier in the energy density of strongly interacting matter, it was explicitly designed to clarify three specific questions raised by the previous experiments, all of them addressing physics topics accessible through the measurement of dilepton production. These three questions are briefly summarized in the following lines:

1. Is the strongly interacting dense medium created in heavy-ion collisions changing the properties of the ρ meson? If so, is it a signal of chiral symmetry restoration? 2. What is the physics mechanism driving the suppression of the J/ψ meson? A thermal phase transition to a quark–gluon plasma or a geometrical transition (percolation) to a system of deconﬁned (but not necessarily in thermal equilibrium) partons?

3. What causes the excess of intermediate-mass dimuons seen in nuclear collisions with respect to the expected sources (Drell–Yan and charm decays) extrapolated from proton–nucleus data? Thermal dimuon production? What is the charm production yield in heavy-ion collisions?

In order to significantly contribute to the clarification of these open questions, NA60 collected indium– indium collisions, at 158 GeV per incident nucleon, during a period of five weeks, at the end of 2003. The first question, raised by the CERES observations, will be studied with considerable statistics (around 1 million signal events, thanks to the high luminosity and very selective dimuon trigger of NA60), a good mass resolution (20 MeV at the ω peak), and a good signal-to-background ratio (between 2:1 and 1:2, depending on the collision centrality). It is important to underline that the phase space coverage of NA60 is very good, down to zero transverse momentum even for dimuons of very low mass. The interpretation of the observations will also benefit from the study of the data in several bins of charged-particle multiplicity, or forward hadronic energy deposited in the zero degree calorimeter. The centrality evolution of the J/ψ production yield and its comparison with the Pb–Pb pattern previously obtained by NA50, should allow us to determine the physics variable driving the suppression mechanism (local energy density, density of partons, number of participant nucleons, etc.), an important step towards answering the second question. Finally, NA60 will also be able to separate the intermediate-mass dimuons into two event samples, one of prompt dimuons and the other of events where both muons come from displaced vertices, thanks to the measurement of the offset of the muon tracks with respect to the collision vertex. These studies will be complemented in year 2004 with proton– nucleus data, essentially aimed at providing a robust reference baseline with respect to which the heavy-ion observations can be compared.

The vastly improved quality of the NA60 measurements, with respect to the previous ﬁxed-target dimuon experiments, is mainly due to the use of radiation-tolerant silicon pixel detectors, which allow us to track the hundreds of charged particles produced in a high-energy nuclear collision and select, among them, those that best match the two muons that gave the trigger. For the indium run, NA60 built a tracking telescope composed of 16 silicon pixel planes, using ALICE1LHCb pixel read-out chips. After an initial setting-up period of a few days, the pixel detectors worked without problems up to the end of the data-taking period. The dimuon mass distributions shown in Fig. NA60–1 give an idea of the quality of the collected data.

Experimental Physics Division 63 Fig. NA60–1: Left: Opposite-sign dimuon mass distributions, before track matching, collected with two settings of the magnetic ﬁeld of the muon spectrometer (less than half of total statistics). Right: Low mass signal dimuons produced in peripheral In–In collisions, after track matching, showing the good mass resolution (less than 1% of total statistics).

WA103

The WA103 experiment, dedicated to the determination of the energy and angle distributions of positrons generated by crystal sources, was carried out on the X5 transfer line of the SPS in 2000 and 2001. In these tungsten crystal converters high-energy electrons (from 5 to 40 GeV) are channelled along the 〈111〉 axis and radiate higher rates of photons than with the ordinary bremsstrahlung mechanism. These photons, in turn, materialize in a large number of electron–positron pairs. The main results obtained in this experiment concern tungsten crystals (4 and 8 mm thick) and an amorphous tungsten converter 20 mm thick. An amorphous disk 4 mm thick was also used, close behind the 4 mm crystal to convert the photons into electron–positron pairs. Most of the data gathered on the positrons concerned incident electron energies of 6 and 10 GeV. The ﬁrst analyses showed:

– A good agreement between simulations and experiment bringing a validation of the former results.

– An important enhancement in photon and positron production along the 〈111〉 axis of the tungsten crystal (referring to a comparison of oriented/disoriented targets of the same thickness). This enhancement being somewhat larger than 3.5 for the 4 mm crystal and than 2 for the 8 mm crystal.

– A dependence of the photon and positron yields on the incident electron energy; yields for the 6 GeV electron beam are slightly lower than for the 10 GeV electron beam. Comparisons between rocking curves (e+ yield with respect to the angle between crystal and beam axes) obtained at 10, 20 and 40 GeV on the positron counters (Fig. WA103–1) show clearly this dependence. An enhancement value of about 2 is observed between 20 and 10 GeV as between 40 and 20 GeV, on-axis orientation (peak of the rocking curve).

64 Experimental Physics Division – A signiﬁcant positron yield value (about 2.5 positron/electron, for the 8 mm crystal with an electron

incident energy of 10 GeV) in the acceptance domain: 5 < E < 30 Mev and pT < 8 MeV/c; such an acceptance domain is often considered in the Linear Collider projects for the positron source. A representation of the measured positron tracks in the (pL,pT) space shows the highest density in the low-energy region, which is of interest for actual positron matching systems between the target and the accelerator (Fig. WA103–2).

The analysis concerning the positrons is, now, completed and applications for linear collider projects that take into consideration the thermic problems are under study. Data on photons is under analysis and the results will soon be available.

2.5 4 kG

2 40 GeV 20 GeV

1.5 10 GeV

0.5

Number of positrons per electron 0 1 1.5233.5 2.5 Rotation angle, degree Fig. WA103–1: The positron rocking curves for 8 mm crystal at B = 4 kG.

12.5 2 11.25 0.025 10 8.75 0.02 7.5 0.015 6.25 5

0.01 per electron, 1/(MeV/c) 3.75 T /dP 2.5 0.005 L

1.25 n/dP 2 0 0 d 10 20 30 40 50 60 70 80

PL, MeV Fig. WA103–2: Positron density in the (pL,pT) space, for 8 mm crystal at 10 GeV.

Experimental Physics Division 65 The CNGS Programme

CNGS1

The OPERA experiment is designed for the direct observation of ντ appearance from νµ → ντ oscillations in the CNGS long-baseline beam from the CERN SPS to the Gran Sasso Laboratory. The measurements of atmospheric neutrino ﬂuxes performed by the Super-Kamiokande experiment indicate a deﬁcit of muon 2 –3 2 neutrinos with a zenith angle distribution consistent with νµ → ντ oscillations with ∆m = 1.3–3.0 × 10 eV (90% C.L.) and full mixing.

The Soudan2 and MACRO and K2K experiments also made observations compatible with this result. Therefore the primary goal of OPERA is to obtain direct evidence for ντ appearance, which would conﬁrm the ν → ν oscillation hypothesis and its nature. An important byproduct is the search for µ e oscillations which θ could lead to a ﬁrst measurement of the mixing angle 13.

A long baseline of 732 km is used between the neutrino source (the CERN beam line) and the detector (located in the Gran Sasso underground laboratory), in order to be sensitive to the oscillation parameters indicated by the Super-Kamiokande data. The CNGS neutrino beam has been optimized for the detection of ντ charged-current (CC) interactions and provides an average νµ energy of about 20 GeV. For the evaluation of the performance of the experiment an integrated ﬂuence of 2.25 × 1020 protons on target is assumed, corresponding to ﬁve years of SPS operation in shared mode. However, ongoing studies at CERN aim to obtain a beam intensity upgrade equivalent to a factor 1.5.

The main principle of the ντ search is the direct detection of the decay of the tau lepton produced by CC interactions. This is achieved by a massive (about 1.8 kton) neutrino target based on the ECC design which combines, in a sandwich-like cell, the high-precision tracking capabilities of nuclear emulsions (two 40 µm layers on both sides of a 200 µm plastic base) and the large target mass provided by the lead plates (1 mm thick). This technique has been recently demonstrated to be effective for tau detection by the DONUT Collaboration.

The basic element of the target structure is the brick, made out of consecutive series of ECC cells with transverse dimensions of 10.2 × 12.7 cm2. Bricks are arranged in planar structures (walls), which are interleaved with electronic tracker planes (Fig. CNGS1–1). These planes are built from vertical and horizontal strips of plastic scintillator 2.6 cm wide. The main purpose of the electronic target tracker is to provide a trigger for neutrino interactions, localize the particular brick in which the neutrino interacted, and perform a ﬁrst muon tracking within the target. The selected brick is then extracted for emulsion development and scanning in a quasi online sequence. Large emulsion areas can be scanned with automatic microscopes equipped with fast track-recognition processors. This technique allows for the search of the tau decay topology and, at the same time, for the measurement of the event kinematic. Track momenta are measured from their multiple scattering in the brick, and electron and gamma energies from shower development.

Figure CNGS1–1 shows the target and the tracker sections which are further arranged in two independent supermodules. Each supermodule is followed by a downstream muon spectrometer. A spectrometer consists of a dipolar magnet made of two iron walls, interleaved by pairs of vertical drift tube planes. Planes of RPCs are inserted between the magnet iron plates to allow a coarse tracking inside the magnet and a measurement of the stopping particles from the upstream target section.

66 Experimental Physics Division Fig. CNGS1–1: Artist’s view of the two supermodules of the OPERA detector.

The OPERA design is optimized to achieve low background levels for the tau appearance search. The experiment aims at the analysis of all the single-prong tau decay modes (e,µ,h). Signal events are classified as long or short decays depending on whether the tau track traverses an emulsion sheet or not. The main background sources are charm production in CC interactions, hadronic interactions in lead, and large-angle muon Coulomb scatterings. These events are rejected by the identification of the primary lepton in CC interactions and either by requiring the presence of a tau-like kink topology (long decays) or by an impact parameter method (short decays). In addition, a kinematic analysis is used to enhance the signal-to- background ratio. Overall a total background of 0.7 events is expected. If νµ → ντ oscillations occur, the average number of detected signal events ranges from 3.1 (at ∆m2 = 1.3 × 10–3 eV2) to 16.4 (at ∆m2 = 3.0 × 10–3 eV2) and corresponds to 7.3 events for the Super-Kamiokande best-fit value (∆m2 = 2.0 × 10–3 eV2, full ν → ν mixing). As far as concerns the search for µ e oscillations, still after a five-year run, OPERA will be able θ θ ∆ 2 × –3 2 2θ to constrain the 13 mixing angle at the level 13 < 0.06 at 90% C.L. (for m = 2.5 10 eV , sin 23 = 1).

The OPERA experiment was approved in 2001. During 2002 the Collaboration completed the detector design, tests and optimization phase resulting in a two-supermodule configuration. Important progress was made in 2003, as foreseen by the construction schedule, in order to finalize the design for the industrial production and enter the construction phase of several parts of the detector. The production chain for the target tracker modules was set up. The design of the brick assembly machine was completed as well as that of the target walls and of the DAQ electronics. A prototype of the brick manipulator system was fully tested. The production of many components of the detector (magnets, RPC, emulsions, target tracker strips, mechanics and readout electronics) was started. About 15% of the emulsion films were produced and an underground facility for their refreshing (the erasure of the cosmic-ray tracks accumulated during the production) was set up in the Tono mine in Japan. Since spring 2003 the detector installation in Hall C of the Gran Sasso underground laboratory has continued with the assembly of the magnetic spectrometers and the RPC system. The OPERA installation will end in 2006, when the first neutrinos from the CNGS beam are expected.

CNGS2 (ICARUS)

The ICARUS T3000 project became an official CERN experiment on 10 April 2003. The issues related to the safety and to the infrastructure at the Gran Sasso Laboratory (LNGS) have been addressed by the Collaboration, by LNGS, and by external specialized companies. The first conclusion is that the first 600 ton module (T600) completely equipped and tested could be installed and operated in LNGS Hall B. The

Experimental Physics Division 67 transportation of the T600 to LNGS is expected by spring 2004. In parallel, the preparation of the site has started. The design of the following two T1200 modules is progressing, as well as the technical design of the muon spectrometer.

Physics

The analysis of the 27 000 triggers collected with a T600 half-module, during a surface test carried out in 2001, is well advanced, as can be seen from the list of papers recently published or submitted for publication:

– Design, construction and tests of the ICARUS T600 detector, submitted for publication in Nuclear Instruments and Methods in Physics Research A on 31/12/2003.

– Measurement of the muon decay spectrum with the ICARUS T600 liquid argon TPC, accepted for publication in European Physics Journal C on 7/1/2004.

– Study of electron recombination in liquid argon with the ICARUS TPC, accepted for publication in Nuclear Instruments and Methods in Physics Research A on 30/10/2003.

– Analysis of liquid argon purity in the ICARUS T600 TPC, Nuclear Instruments and Methods in Physics Research A516 (2004) 68.

– Observation of long ionizing tracks with the ICARUS T600 ﬁrst half-module, Nuclear Instruments and Methods in Physics Research A508 (2003) 287–294.

As an example of the physics analysis being conducted, we brieﬂy describe the measurement of the Michel electron spectrum: a sample of more than 3000 stopping muons was fully reconstructed in three dimensions and analysed. Figure CNGS2–1 shows the measured Michel electron spectrum obtained by exploiting the spatial and calorimetric reconstruction capabilities of the liquid argon detector. The measurement of the Michel ρ gives 0.72 ± 0.06(stat.) ± 0.08(syst.) in agreement with the Standard Model value (= 0.75). Energy resolution for electrons below 50 MeV has been found to be 11%/√E ⊕ 2%.

Fig. CNGS2–1: Energy spectrum of electrons from stopped muons in a T600 module.

68 Experimental Physics Division The Muon Spectrometer

The proposal to upgrade the ICARUS detector with an external muon spectrometer was submitted to the SPSC and the LNGS Scientiﬁc Committees in October 2003 [CERN/SPSC 2003-030 (SPSC-P-323-Add.1), LNGS-EXP 13/89 add. 3/03].

The muon spectrometer is relevant for physics at the CNGS beam. The main topics to be addressed with ν → ν νµ → ν the artiﬁcial neutrino beam are µ τ and e oscillations. Since most of the muons escape the LAr detector, we proposed to complement ICARUS with an external magnetized muon spectrometer in order to have a precise muon momentum measurement and charge discrimination. Its resolution should be below 20% in order to match the resolution introduced by nuclear effects like Fermi motion. This apparatus is required to have an accurate knowledge of the beam composition, as well. The baseline design adopted for the muon spectrometer consists of a non-instrumented part made of almost saturated iron at 1.8 T that provides two bending regions, each of them 1.5 m long. Track deﬂection is measured in four muon stations, made of chambers with four staggered layers of drift tubes each. A precise t0 determination is given by an RPC plane located in front of the magnet (see Fig. CNGS2–2).

Fig. CNGS2–2: Schematic of the muon spectrometer of the ICARUS experiment.

The East Hall Programme

PS212

The purpose of the DIRAC experiment is to determine with an accuracy of 5% the difference between the π+π– I = 0 and I = 2 S-wave scattering lengths from a measurement of the lifetime of an exotic -atom (A2π ) . An accurate measurement of |a0-a2| will submit the current understanding of chiral symmetry breaking of QCD to a crucial test, and provide information about the value of the two-ﬂavour quark condensate.

The DIRAC apparatus consists of a double-arm magnetic spectrometer designed to measure π+π– pairs of low invariant mass.

In 2003 DIRAC was allocated three months of running to clarify the sources of systematic errors. Additionally we made tests on a micro-drift chamber. In detail we performed:

Experimental Physics Division 69 1. Data taking with two Ni targets, one being a single (single-layer) 98 µm thick foil, the other consisting of 12 foils (multilayer). 2. Direct measurement of multiple Coulomb scattering. 3. Running of the DIRAC experiment with a micro-drift chamber under high intensity (test run).

In the three months we effectively obtained 78 days of proton beam and collected 3.1 × 108 ππ triggers. Because of similar problems to 2002, the beam energy was only 20 GeV/c and the number of spills was signiﬁcantly lower (on average 1.5 spills instead of 3, but somewhat longer spill duration and better duty cycle). The lower energy alone caused a loss of atomic pairs of more than 25%. The test beam conditions were standard, however, with an intensity twice as high as in our previous runs.

Point 1. Data were taken by alternating single and multilayer (12 foils, each 7.5 µm thick, 1 mm inter- spaced) Ni targets, of identical total thickness. This procedure produces identical backgrounds but different atomic signal strength, because

– the beam interaction rate is the same,

– the backgrounds are the same,

– the yield of produced A2π is the same, – the integral multiple Coulomb scattering is the same,

– the A2π break-up probability is smaller, i.e., the atomic pair signal is smaller.

In an appropriate combination of the two measurements, the background can be made to disappear and the signal alone remains, or the signal can be made to disappear and only the background remains. From a preliminary analysis of the 2002/3 data we present in Fig. PS212–1 the difference of single and multilayer targets. The backgrounds clearly cancel in the difference but not so the signals. With respect to 2002 we have not achieved our goal of tripling the statistics but remained a factor of two lower. In Table PS212–1 we present the preliminary results on the number of events from the difference measurement. The errors have improved by about 20%.

Fig. PS212–1: Difference single–multilayer for total (Qtot) and longitudinal (QL) relative momentum of the ππ pair. The solid lines represent Monte Carlo shapes for the expected signal.

70 Experimental Physics Division Table PS212–1: Atomic signal strength for the difference of the single–multilayer spectra,

separated for Q and QL as obtained from a ﬁt of the signal shape to the spectra. The last column requires the same signal strength in Q and QL

QQL Q & QL 2002 820 ± 120 1010 ± 150 890 ± 120 2002+2003 1400 ± 150 1590 ± 200 1480 ± 150

Point 2. The present uncertainty in the description of the multiple Coulomb scattering in the target and all the material of the apparatus contributes signiﬁcantly to the magnitude of systematic errors. We have directly measured multiple scattering in all the relevant materials, in parallel with the single–multilayer measurements. Targets with appropriate thicknesses were placed just behind drift chamber No. 3. The scattering angle was measured with an estimated precision of 1% using the accurate tracking properties of the drift chamber system. The resolution function was obtained from tracks not passing the scattering targets and a deconvolution procedure provided the multiple scattering angular distributions. A preliminary analysis with only 10% of the data shows that the measurement is not in disagreement with the standard Moliere description as far as the central part of the distribution is concerned. Analysis with full statistics will provide more detailed information on the tails of the distributions.

Point 3. The micro drift chamber (MDC) is a fast drift chamber with high double-track resolution. It has a cell size of 2.54 × 2.00 × 80 mm3 and 32 cells per plane. Two planes shifted by half a cell form an X-, Y-, or U-plane. The chamber is operated with 2 atm overpressure. The maximum drift time is 25 ns. Spatial resolution is (22 ± 4) µm. Double-track resolution is expected to be 100 µm. Its total thickness is only × –3 5 10 X0. In a test in 2003 we replaced the MSCGs by a system of 18 planes of MDCs and ran the full DIRAC spectrometer. The beam intensity was 1.6 × 1011 pps, i.e., two times higher than for ordinary running. The system ran successfully for one week. However, the high rate of heavily ionizing particles caused too high currents in some chambers, and after two weeks we stopped data taking because 30% of the chambers had to be switched off. We are now working on a new readout scheme which should allow for lower currents and thus for lower high voltage. The new MDC system is a promising tracking device designed for high proton intensities.

In parallel we have worked on data processing and analysis. Up to now we have collected about 14 000 atomic pairs with restrictive cuts and 18 000 with loose cuts, with Ni and Ti targets.

PS214

The HARP experiment, approved by CERN on 17 February 2000, is part of the European R&D towards the neutrino factory. Data were taken in 2001 and 2002 successfully collecting more that 30 TB of data. HARP is performing a systematic study of hadron cross-sections at several beam momenta (from 2 GeV/c to 15 GeV/c) and on a large number of solid and cryogenic targets.

The main motivation of the experiment is twofold: to acquire adequate knowledge of pion yields for an optimal design of the proposed neutrino factory, and to improve substantially the calculation of the atmospheric neutrino ﬂux which is needed for a reﬁned interpretation of the evidence for neutrino oscillation

Experimental Physics Division 71 from the study of atmospheric neutrinos in present and forthcoming experiments. HARP (Fig. PS214–1) is a full-acceptance apparatus, capable of collecting a large number of different momenta and targets thanks to its high-rate capability, corresponding to a few million events per day. The desired overall precision of a few per cent requires keeping the efﬁciency under control down to the level of 1%, primarily by redundancies in the acceptance regions of the detectors.

Fig. PS214–1: Schematics of the HARP set-up.

In addition to the standard set of target geometries and materials, HARP also measures production cross- sections on special targets for the K2K and MiniBooNE Collaborations. Owing to the termination of Objectivity support at CERN, a migration project had to be developed in 2003 to move the HARP data and software from the Objectivity Object Database System to the Oracle Relational Database System. The successful migration of more than 30 TB of HARP data to Oracle guarantees full database functionality such as CERN-based DST production, data selection, and access. At the same time, an iDST format was used (based on MySQL) for data distribution in the collaboration.

In 2003 major progress was achieved in the understanding of all the sub-systems of the apparatus. In particular, the various sub-detectors of the forward spectrometer (drift chambers, Cherenkov, time-of-flight, electron-identifier and muon identifier) have all been calibrated and their performance is well understood. In addition, a new track reconstruction algorithm for the forward region, with an efficiency better than 90% was developed and its performance measured from the data themselves. The momentum resolution is shown in Fig. PS214–2. A software tool based on the Kalman method was developed allowing navigation along the full spectrometer; the Monte Carlo description of the apparatus based on GEANT4 reproduces the experimental data well.

A particularly important physics case is the measurement of the hadronic production cross-sections of the MiniBooNe and K2K replica targets, given the immediate interest for those experiments. HARP will present these cross-sections and results in early 2004. In 2003 the whole apparatus was dismounted with the exception of the TPC.

72 Experimental Physics Division This detector was the subject of a large calibration campaign of hardware measurements and data analysis. This has proven to be necessary to make physics analysis possible. Cosmic-ray data and data taken with radioactive sources were used to fully understand and improve the detector performances. As example (Fig. PS214–3) shows the energy spectrum obtained with a radioactive iron source where peaks at 5.9 keV and 3 keV are clearly visible.

ID 1000000 Entries 20613 Mean 0.5189 1000 RMS 0.1928 78.94 / 26 Constant 992.3 Mean 0.5978 800 Sigma 0.1248

600

400

200

0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Energy [keV/10]

Fig. PS214–2: Momentum resolution in the Fig. PS214–3: Energy spectrum obtained with forward direction. a radioactive iron source.

The AD Programme

AD1

In 2003, after the ﬁrst observation of cold antihydrogen in 2002, ATHENA has concentrated on trying to learn more about the mechanism(s) underlying the formation of antihydrogen when low-energy antiprotons are merged with a dense, cold and magnetized positron plasma. This year has also seen ATHENA make important changes to its apparatus and implement a number of on-line methodological improvements (plasma diagnostics and temperature control, sideband excitation of the radial antiproton motions, improved-efﬁciency mixing cycles, positron manipulations, improved access to the apparatus to allow the introduction of laser light into the system) that will have an impact on the controlled creation and study of antihydrogen.

The initial observation of cold antihydrogen by the ATHENA experiment was based on a complete geometrical reconstruction of the annihilation products of antihydrogen atoms on an event-by-event basis, in which both antiprotons and positrons were detected via their annihilation products. In an analysis based on a complete description of the ATHENA apparatus, we have shown that other observables (among them the total trigger rate), with a lower speciﬁcity to antihydrogen, but higher reconstruction efﬁciency, produce consistent

Experimental Physics Division 73 estimates of the production rates of antihydrogen atoms. A combined analysis of these signals has shown that in 2002 and 2003, ATHENA has produced about 1.2 million antiatoms from 8 million trapped antiprotons, with a yield of about 15%.

ATHENA has obtained a detailed picture of the antiproton dynamics during cooling through positrons, and throughout the time-regime when antihydrogen is efﬁciently formed. The onset of antihydrogen production, as monitored by the detector trigger rate, was found to depend on the dynamics of this cooling process (Fig. ATHENA–1).

Fig. ATHENA–1: a) Trap potential on axis before injection, after injection, and during mixing. b) Detector trigger rate versus time relative to injection for two

different injection energies Einj corresponding to different antiproton kinetic energies.

Investigations of the dependencies of antihydrogen formation on the positron plasma temperature and density can give important clues as to the likely formation mechanism(s) and, by inference, the range of quantum states formed. The positron plasma temperature could be changed and its increase measured in a controlled way by radiofrequency excitation of the axial dipole mode of the plasma. Mixing was carried out at different positron plasma temperatures, and antihydrogen production was detected via different observables (Fig. ATHENA–2). A clear decrease of antihydrogen production with the positron plasma temperature is visible. However, a simple power-law scaling does not ﬁt the data. The naïve three-body temperature dependence (T–9/2) is not consistent with the data, and the expected predominance of this mechanism below ~100 K is not supported by the leveling-off at low temperatures. The fall-off in antihydrogen production with plasma temperature is slow enough to be still measurable at room temperature in the ATHENA apparatus. This observation, coupled with the behaviour at high temperature, suggests that the radiative mechanism cannot be completely excluded by ATHENA, leading to anti-atomic states that are more tightly bound than those observable using ﬁeld ionization techniques. Nevertheless, the simple radiative antihydrogen production rate prediction is not obviously compatible with our data, the former being an order of magnitude lower.

The spatial distribution of the emerging antihydrogen atoms can also provide insights into the nature and dynamics of the formation process, and by inference the distribution of states formed. The model that best matches the measurements is a slightly anisotropic distribution, with a small radial excess, i.e., the spatial distribution is slightly ellipsoidal. The near-isotropic nature of the distribution suggests that the antihydrogen is mostly formed when the antiprotons are diffusing randomly in the positron plasma. The combined electric ﬁelds of the plasma and trap set lower limits on the binding energies of the emerging antihydrogen atoms,

74 Experimental Physics Division since some weakly bound atoms will be field-ionized before they drift to the trap walls. The binding energy limit is estimated to be 2.1 meV in our trap and plasma conditions. Three-body combination of an antiproton and a positron may produce more strongly bound states than this. Calculations suggest also that weakly bound states would tend to emerge along the lines of the magnetic field. A preliminary conclusion is therefore that three-body recombination, the effect of the magnetic field, the positron plasma polarization by the injected antiprotons, and the role of the guiding centre atoms need to be considered in detail in the analysis of our data. This work is in progress.

Fig. ATHENA–2: Temperature dependence of antihydrogen production using different signals for antihydrogen production. Data are normalized to the 15 K sample, from which the absolute positron temperature is obtained using the measured values of ∆T. (a) The opening angle excess for the high statistics samples. (b) The number of triggers for all samples (‘hot mixing’ background). (c) The peak trigger rate for the high statistics samples.

AD2

The year 2003 was another year of good progress for ATRAP – like 2001 and 2002 before. In 2001 we demonstrated positron cooling in a nested Penning trap – the only device and technique used to produce slow antihydrogen so far. In 2003 ATRAP and ATHENA both detected the antihydrogen produced in this way using very different detection techniques. ATRAP highlights for 2003 were an observation of more deeply bound states of antihydrogen, the ﬁrst measurement of the velocity of slow antihydrogen atoms, and the ﬁrst use of lasers to control the production of cold antihydrogen.

Experimental Physics Division 75 ATRAP’s field ionization method provided the first measurement of a distribution of internal antihydrogen orbits, reported in ATRAP’s second paper in Physical Review Letters for 2002. A first demonstration of driven antihydrogen production increased the antihydrogen production rate enough so that an electric prestripping field could be inserted between the antihydrogen production and detection volumes to analyse the internal orbits and state of the antihydrogen. At least eight theory papers were triggered by the observations of slow antihydrogen in 2002, and by the distribution of antihydrogen states measured by ATRAP in particular.

ATRAP remains steadfast in its pursuit of the long-term goal that has been advertised as the purpose of the antihydrogen experiments – to use accurate spectroscopy to compare antihydrogen and hydrogen atoms at extremely high accuracy. We are gratiﬁed by the substantial progress that brings us closer to this important, challenging and distant goal.

1. A careful study of what we learn from the field ionization of antihydrogen in a strong magnetic field is in press at Physical Review Letters. The study confirms the usefulness of ATRAP’s field ionization method, and prepares the way for more extensive measurements of the distribution of antihydrogen states. 2. A Comment to Physical Review Letters claimed that our antihydrogen state analysis was accurately described by a Monte Carlo simulation of antihydrogen production. While we would be delighted if this claim were true, our analysis suggests that this claim is somewhat premature. The Comment and the ATRAP response are in press at Physical Review Letters. Enough progress has been made in the understanding of slow antihydrogen that attempts to compare theory and experiment are now beginning. 3. A method for measuring the density and spatial distribution of the trapped antiprotons and trapped positrons used to make slow antihydrogen was completed. This is crucial for quantitative understanding of antihydrogen production. (Publication in progress.) 4. A quantitative analysis of the positron cooling of antiprotons, the core techniques used to produce all the antihydrogen observed so far, has been completed. Obtaining good agreement between our measurements of the cooling time could be obtained only by a substantial adjustment of a critical cutoff parameter – to a value that seemed more plausible to us, a conclusion with which the theorists now agree. (Publication in progress.) 5. We succeeded in greatly increasing the number of positrons that we had available for experiments to about 5 million – by reusing the positrons from repeated cycles of antihydrogen production. 6. More deeply bound antihydrogen states have been observed – states that survive an ionization field of 360 V/cm, and thus have a radius of 0.25 microns or less. This is exciting first evidence of antihydrogen atoms that are deeply enough bound to have chaotic trajectories, rather than guiding centre atom trajectories. (Publication in progress.) 7. We have successfully measured the velocity of slow antihydrogen for the first time. To do so we sinusoidally varied our prestripping field, and changed the frequency at which this field was oscillating. Faster antihydrogen atoms could pass through the prestripping field while the field was at a low value, while slower antihydrogen atoms could not help but be ionized by the prestripping field. Our first demonstration of this technique analysed only the speeds of the most weakly bound antihydrogen states that we observed, and these atoms were moving faster than we would have hoped. (Publication in progress.)

76 Experimental Physics Division 8. We have succeeded in demonstrating a second, entirely new method for producing slow antihydrogen. A pair of lasers selects the antihydrogen states that are produced, by exciting cesium atoms, which then transfer their energy by resonant charge exchange collisions – first to positronium atoms and then to antihydrogen. Our demonstration is a clear proof of principle – close to expectation – though only a relatively small number of antihydrogen atoms were observed. This method is an important alternative insofar as the antihydrogen produced by it should be as cold as the stored antiprotons used to form it. (Publication in progress.) 9. Beside the successful introduction of two lasers for the resonant charge exchange production of cold antihydrogen, we briefly introduced another laser with which we hope to look for antihydrogen states that are more deeply bound than we can ionize with our field ionization method. The idea is to excite the more deeply bound states up to states which we can field-ionize and detect with our field ionization method. 10. We have installed the major components of the much larger ATRAP II apparatus in our second experimental zone. The large-bore superconducting solenoid has been operated. An annihilation detector and most of its electronics were installed. A large-bore insert dewar has been partly installed.

The ultimate objective of antihydrogen research is precise spectroscopic comparisons of antihydrogen and hydrogen atoms. This requires useful antihydrogen atoms that are in the ground state and are moving slowly enough that their magnetic moments can be captured in a trap. For all the incredible publicity that cold antihydrogen has received, and the large numbers of atoms that are sometimes celebrated, no useful antihydrogen atoms have yet been demonstrated. ATRAP is now focused upon demonstrating the production of useful antihydrogen.

AD3

ASACUSA has for some years been tightening the limit on any possible difference between the antiproton charge and mass and those values for the proton in order to test the CPT theorem’s assertion that matter and antimatter particles have identical properties. As reported in the 2002 Annual Report this is done by tuning a laser beam’s frequency to resonate with the difference in energy between pairs of energy levels in the antiprotonic helium atom – a helium nucleus (or alpha particle) orbited by one electron and one antiproton (pHe++e–). The resonant frequency causes a quantum jump between the two levels, and its value is a measure of the square of the antiproton charge, times its mass. This can be combined with an independent measurement of the charge-to-mass ratio (given by its orbital motion frequency in a magnetic ﬁeld) to arrive at values for the charge and mass separately, relative to those of the proton. In 2003, the previous best result – that any such difference must be smaller than sixty parts per billion (ppb) – was tightened still further to ten ppb (M. Hori et al., Phys. Rev. Lett. 91 (2003) 123401). What made the improved precision possible was that a Radio Frequency Quadrupole (RFQD) was used to reduce the AD antiproton kinetic energy from 5.6 MeV to 65 keV. The reduced antiproton energy allowed the antiprotonic atoms to be formed in very low pressure (0.04 mb) helium gas, which in turn meant that systematic errors on measured laser frequencies, resulting from their collisions with ordinary helium atoms, could be better estimated and corrected for.

The 10 ppb limit may soon go down by one order of magnitude or more, since ASACUSA is presently installing a yet-higher-precision laser system for the 2004 run period. At such levels of precision a fascinating new aspect of these experiments should appear, since if the antiproton mass is related to the electron mass

Experimental Physics Division 77 instead of the proton mass, the antiproton will then be a better-known fundamental particle than the proton itself. This seemingly paradoxical situation comes about because no ‘protonic antihelium’ counterpart to the antiprotonic helium atom is available with which the corresponding proton experiments could be made.

Further experiments completed in 2003 are about to bring another exciting new prospect into sight. These showed that it is possible to create antiprotonic helium ions in a state suitable for laser spectroscopy of the kind described above. The important thing here is that this pHe++ ion is a two-body system, while the neutral atom pHe++e– comprises three bodies. The properties of two-body systems are, in principle, exactly calculable mathematically, while those of three-body systems can only be solved approximately, using extremely complex calculations with powerful computers. The results of these calculations are consequently subject to their own errors, which beyond a certain level of precision can exceed those of the experimentally determined resonant laser-frequencies. Furthermore, the pHe++ ion is the nearest thing physicists have ever had at their disposal to the semi-classical Bohr-type atom used to introduce undergraduate students to the concepts of atomic physics – in many respects it is even more hydrogenlike than the hydrogen atom itself.

Further progress was made by ASACUSA in 2003 in many other directions. In particular, the world record was achieved of confining 4.5 million antiprotons in an electromagnetic trap. This is an important step towards the ASACUSA goal of producing antiproton beams with electronvolt energies, to be used for a wide variety of further experimental studies. The first steps in this direction were taken with the extraction of some 50 000 antiprotons at 250 eV energy from a confined sample containing approximately one million antiprotons. Work is under way to increase this extraction efficiency. ASACUSA also supplemented its recent investigations of the stopping power of metallic targets like carbon, aluminium, nickel, and gold with new measurements on lithium fluoride at energies as low as 2 keV. Such measurements are important in elucidating the interaction properties of antiprotons with atoms and molecules, since these are expected to differ at extremely low velocities from those of the proton on account of the antiproton’s negative charge.

Finally, at the request of the SPSC, ASACUSA continued its study of the feasibility of an experiment to measure the ground-state hyperﬁne structure of the antihydrogen atom, one of the collaboration’s longer-term goals.

The nTOF Programme

nTOF-03, nTOF-04, nTOF-06, nTOF-08, nTOF-09

The 2003 campaign at nTOF started with the measurement of the 139La(n,γ) cross-section, a part of the nTOF-08 experiment. The aim of this measurement is to improve the accuracy of presently available data needed to meet the quality required in modeling s-process nucleosynthesis. In particular, the 139La(n,γ) reaction rate can be used as a diagnostic tool for neutron exposure and neutron ﬂux during He-burning stages of stellar evolution. In fact, the small capture cross-section expected for 139La acts as a bottle neck in the s-process ﬂow which leads to the formation of heavier nuclei. Its accurate knowledge is therefore mandatory for the stellar evolution modelling of the s-process nucleosynthesis.

78 Experimental Physics Division The measurement was performed with the standard set-up of capture measurements with the two C6D6 gamma-ray detectors placed 8 cm upstream with respect to the sample position, perpendicular to the neutron beam line.

The 139La sample was encapsulated in a 20 mm Al can. A measurement of the empty can was performed in order to evaluate the background component of the measured count rate. In addition, a measurement of a 0.5 mm thick Au sample was performed in order to obtain the capture yields relative to this standard.

The measurements of all the stable Zr isotopes, 90,91,92,94,96Zr(n,γ) cross-sections, were subsequently performed during the 2003 summer period. These measurements are also part of the nTOF-08 experiment. The motivation for accurate neutron capture cross-sections for these isotopes is the s-process nucleosynthesis modelling, in mass region (A ≈ 90).

In addition to nuclear astrophysics, a high priority requirement for accurate capture cross-sections of the Zr isotopes comes from the Nuclear Data community, where these cross-sections are required since zirconium constitutes an important component of the alloys used as structural material in nuclear reactors (cladding of fuel elements).

The measurement of the 93Zr(n,γ) cross-section, which is relevant for the nuclear astrophysics aspects as well as for nuclear technologies (93Zr is an important ﬁssion product) was postponed because of a delay in the procurement of the radioactive sample in a form suitable for use in the nTOF experimental area.

91Zr(n,γ) 1

10–1 Counts/pulse

10–2

103 104 105 106 Neutron energy [eV]

Fig. nTOF–1: Capture gamma-ray count-rate from the 91Zr(n,γ) measurement. The relevant energy range from 0.1 keV to 1 MeV is shown. This is an example of the data obtained at nTOF for the capture cross-section measurements of all the stable zirconium isotopes 90,91,92,94,96Zr(n,γ).

Experimental Physics Division 79 The standard capture set-up was used for these measurements. The procedure used for the background determination, with the measurement of the Al can and for the normalization, based on the Au standard, was adopted in the present case as well. As an example, the rich resonance structure of the capture cross-section of 91Zr is shown in Fig. nTOF–1. As one can see, the excellent nTOF energy resolution allows for a clear separation of neutron resonances in the energy region of interest for the present measurement. The data shown in the ﬁgure covers only approximately 10% of the total counts registered during the measurement.

The series of capture measurements continued with the measurement of three Mg samples. This is part of the nTOF-03 experiment which included the 151Sm(n,γ) measurement performed in 2002. Reliable cross- sections for the three stable Mg isotopes, 24,25,26Mg, are important for the interpretation of the abundance ratios found in pre-solar grains and carry information on the 22Ne(α,n)25Mg reaction as a neutron source for the s-process. The Mg samples where encapsulated in an Al can of 22 mm diameter. The masses of each MgO2 powder were, respectively, 5.2 g, 3.19 g and 3.23 g, for natMg, 25Mg and 26Mg.

The capture cross-section measurements continued with the measurements of the three isotopes 186,187,188Os. This measurement represents the core measurement of the nTOF-04 experiment, The Re/Os clock revisited. The aim here is to determine accurately the capture cross-sections of 186Os and 187Os. These two nuclei can be produced only during the s-process. In turn, a fraction of the 187Os abundance observed in Nature is due to the slow β– decay of 187Re, with a half-life of 43.2 × 109 years. It is therefore possible to derive information on the time duration of the nucleosynthesis, or on the time duration of the chemical evolution of our galaxy, from the analysis of the s-processing of 186Os and 187Os. The crucial nuclear physics information still missing here is in the accurate neutron capture cross-sections of these two nuclei (or, more in particular in their stellar capture cross-section ratio).

The samples for these measurements were obtained on loan from the Oak Ridge National Laboratory. The measurement of the 188Os(n,γ) cross-section was performed ﬁrstly because this isotope is present in a sizeable quantity in the other two samples, and the knowledge of this cross-section is required for correcting the measured count rates of the 186,187Os samples. In addition, the result of this measurement can be used to check experimentally some of the model parameters required in the calculation of the stellar rates.

The Os samples were encapsulated in Al, as for some of the previous measurements. An example of the experimental data obtained in this measurement is shown in Fig. nTOF–2.

In addition to the measurements described above, a series of calibration measurements were performed. In particular, dedicated measurements of the capture in 238U, Ir, and S were performed in order to derive experimentally the time-of-flight to energy conversion law. This is in first approximation related to the geometrical length of the TOF path. However, an energy-dependent component due to the moderation process in the target-moderator assembly starts to play a role in the energy region above 1 keV and needs to be determined experimentally. The nuclei listed above have resonances which are neutron energy standards in a wide energy range. They can be used to derive the energy-dependent component of the effective flight path length.

80 Experimental Physics Division 187Os(n,γ)

10–1 Counts/pulse In-beamIn-beam γ-ray-ray 10–2

AlAl 10–3 103 104 105 Neutron energy [eV]

Fig. nTOF–2: Count rate of the 187Os(n,γ) measurement at nTOF. In the ﬁgure, the two background components expected in this measurement are shown separately. The events due to the Al canning are well below the measured values. The component due to the gamma rays present in the neutron beam is shown as well. The total count rate is in the entire energy range well separated and above the measured background components.

Finally, a test of the BaF2 crystal to be used in the construction of the nTOF Total Absorption Calorimeter (TAC) was performed. This test allowed for an experimental determination of the response of the BaF2 detectors in the nTOF EAR-1. An assembly of eight crystals was used in the test and parameters such as the recovery time of the detector after the prompt ﬂash and the expected count rate to be transferred by the data acquisition system were obtained.

The total number of protons delivered by the CERN PS for the capture campaign was 9 × 1018.

The last period of the run was dedicated to ﬁssion cross-section measurements, with the neutron beam collimated at 8 cm diameter. Three detectors were installed in the EAR-1: two upgraded version of Fast Induction Chambers (FICs) and the Parallel Plate Avalanche Chambers (PPACs). The upgrading of the FIC detectors allowed the mounting of very radioactive unsealed targets inside the chambers. Thanks to an agreement with Russian Institutes providing most of the radioactive samples expected for the nTOF-06 and nTOF-09 programme, the following isotopes were measured: 233,236U, 237Np, 241,243Am, and 245Cm. The count rate statistics were improved for 232Th, 234U and for the references 235,238U. According to a preliminary data analysis, the very good energy resolution of the facility was conﬁrmed leading to the observation of resolved resonances for almost all isotopes. For the isotopes related to the thorium cycle there are good data with perfect resolution for 234U and 237Np. The resonances of 235U can be resolved for energies up to 20 keV. Concerning the transuranium isotopes, there are very good data and enough statistics for 245Cm but additional statistics are needed for the other isotopes.

Experimental Physics Division 81 A preliminary analysis of the data obtained with the PAPCs detectors shows that a reliable set of cross- sections can be obtained from these measurements as well. The targets used in the PPACs chamber in 2003 were 232Th, 233,234U and 237Np, in addition to the standards 235,238U and 209Bi.

The total number of protons delivered by the CERN PS for the capture campaign was 3.2 × 1018. An additional run of ﬁssion measurements for a total of four weeks is foreseen for the 2004 campaign.

nTOF-07

The interaction of neutrons with nuclei in the neutron energy region from thermal to a few tens of MeV has for long been of primary interest for conventional nuclear reactor physics. But neutron-induced reactions are also important in several other ﬁelds, including astrophysics and fundamental symmetries. In addition, important information on level densities, a key ingredient in many nuclear reaction codes, can be obtained directly from neutron resonance spectroscopy.

The neutron time-of-flight facility, nTOF, at CERN with its high instantaneous neutron flux, high resolution and low background is well suited for high-quality neutron cross-section measurements. The scientific programme of the nTOF Collaboration includes the measurements of neutron capture, fission and (n,xn) reaction cross-sections for nuclear technology, nuclear astrophysics, and fundamental nuclear physics.

Precise measurements of the neutron capture cross-sections of nuclei relevant for the thorium-based nuclear fuel cycle are of great interest for applied physics. Specifically, a more detailed knowledge of the (n,γ) cross-section for the isotopes 232Th, 231Pa, 234U and 236U is required for the possible implementation of the thorium fuel cycle in existing and innovative nuclear power devices. A thorium-based fuel cycle may significantly reduce the production of nuclear waste as compared to the actual uranium-plutonium-based fuel cycle in currently operating nuclear fission reactors.

From a fundamental physics point of view, precise measurements of the 232Th (n,γ) cross-section are desirable for the study of parity-non-conserving (PNC) effects in nuclei. In particular, they would lead to a reﬁned description of low-energy resonances and would allow an improved estimation of the mean value of PNC matrix elements. The high radioactivity stemming from the decay products of these isotopes has very much hindered or made impossible accurate capture measurements in the past. A signiﬁcantly better situation is given at the CERN-nTOF facility which has a very favourable duty cycle for measurements on radioactive targets.

The experiments of proposal nTOF-07 make use of this advantage and intend to measure the cross-sections of 232Th (n,γ), 231Pa (n,γ), 234U (n,γ) and 236U (n,γ) at the CERN nTOF facility in the neutron kinetic energy range from 1 eV up to 1 MeV. The proposed experiments are part of the scientiﬁc programme of the contract FIKW-CT-2000-00107 between the European Commission and the participating institutes.

During the year 2002, data were taken, in addition to other experiments that are part of the nTOF programme, for the cross-section measurement of 232Th (n,γ) at the nTOF facility. The experiment was performed using two optimized low-mass C6D6 gamma-ray detectors together with a pulse-height weighting technique in order to make the detector efﬁciency for the (n,γ) reaction independent of the details of the reaction gamma-ray spectrum.

82 Experimental Physics Division The data analysis of the 232Th (n,γ) measurement is now to at the point of cross-section extraction in the unresolved resonance region. At lower energies, a detailed resonance analysis will allow the reconstruction of the cross-section. The reaction rate of the measured spectrum is shown in Fig. nTOF-07–1. The remaining capture experiments of nTOF-07 will be performed in 2004.

232 3 Th(n,γ) 10 scattered photon background radioactivity background

102 dn/d(lnE)

counts per bunch 101

100 100 101 102 103 104 105 neutron energy (eV) Fig. nTOF-07–1: The count rate spectrum from the measurement of the 232Th (n,γ) cross-section, together with a ﬁrst rough estimate of the background due to radioactivity and due to scattered photons.

The ISOLDE Programme

Nuclear Physics

IS371

Studies of nuclei in the drip-line region continue to attract a large interest worldwide. This originated in the realization that the loose binding of nuclei near the border of stability and their large excess of neutrons or protons give rise to phenomena such as halo states, clusters, and new shell structures. Both on the experimental and theoretical sides there is steady progress which has been summarized in several recent review articles. The analysis of available experimental data, as well as future advances in the theoretical understanding of drip-line nuclei, is still hampered by the absence of information about the quantum characteristics of their nuclear states. It is well known that the understanding of these so-called Borromean nuclei requires information about the structure of their binary sub-systems. An examples is 11Li, where one needs knowledge of the 11Li(9Li+n) structure. The typical approach in order to obtain this kind of information is to produce the nuclear species in some reaction. When the nuclei of interest are very far from both target and beam nuclear species, as is the case for drip-line nuclei, it becomes increasingly difﬁcult to use conventional stable beams for this production. This is exempliﬁed in several recent experiments where complicated, largely unknown reaction mechanisms have been employed. One possible way to proceed is to use radioactive beams combined with simple, well-understood reactions to populate the states in question.

Experimental Physics Division 83 In this experiment we are studying the low-lying states in 10Be produced by an ISOLDE 9Li-beam accelerated in the REX-ISOLDE complex to 2.25 MeV/u and allowed to react in a proton target of suitable thickness. A preliminary analysis of the data taken during the IS371 beamtime in October 2003 has been carried out. The experimental set-up is described in Fig. IS371–1. We have studied the protons elastically scattered at forward angles by a 9Li beam, as this is stopped in a polyethylene target of 105 µm thickness. Two mechanisms contribute in the reaction: Rutherford and nuclear (resonance) scattering. We are interested only in the latter which reﬂects resonances in the 9Li+p system (i.e. what we refer to as unbound states in 10Be), and among those mainly the T = 2 states, which are the analogues of low-lying states in 10Li. Owing to the long range of the Coulomb interaction, Rutherford scattering takes place primarily at large impact parameters which leads to a (diverging) maximum of the cross-section at a proton scattering angle of 90° in the laboratory system. We thus restrict the analysis to protons that emerge at small angles to the beam in order to favour nuclear scattering. This at the same time ensures a minimum energy loss for the protons, when passing through the target, and allows us to measure the excitation function towards lower energies. By detecting the angle and energy of a scattered proton, one can calculate the CM energy at which the reaction took place, and thereby the corresponding 10Be excitation energy. The result of this test beam time looks very promising and the real experiment will take place during 2004–05.

Fig. IS371–1: Set-up in the reaction chamber mounted at the 2nd beam-line of REX. After passing through a sequence of collimators of 3 to 5 mm diameter in the beam-line and the chamber itself, the REX beam was stopped in a polyethylene (PE) foil of 105 µm thickness. The reaction products were detected in three 50 × 50 mm2 Double Sided Si Strip Detectors (DSSSD) backed by thick, 50 × 50 mm2 single-area surface barrier detectors to form detector telescopes. Centred at 0° scattering angle DSSSD1 covered the angular range of 0–30° with a resolution of about 2°. The two outer telescopes were centred at 54° and thereby covered 35–70°. Protons emitted at scattering angles above 50° did not escape the target. At 2.25 MeV/A beam energy the average range of a 9Li ion is 89 µm and the longitudinal straggling only 3 µm. Consequently, all 9Li ions were stopped inside the target.

84 Experimental Physics Division IS381

Isospin mixing in N ≈ Z nuclei is an important phenomenon in nuclear physics that has recently gained both theoretical and experimental interest. It also forms an important nuclear physics correction in the precise determination of the ft-values of T = 1 superallowed 0+ → 0+ β transitions, which are used, for example, for testing CVC and the unitarity of the Cabibbo–Kobayashi–Maskawa quark-mixing matrix. The experiment IS381 investigates isospin mixing in the N ≈ Z region by determining the isospin-forbidden Fermi component π π in Gamow–Teller dominated J → J β transitions through the observation of anisotropic positron emission from oriented nuclei.

71 59 In the past year the analysis of the data previously obtained in the decay of As (t1/2 = 65 h) and Cu 59 (t1/2 = 82 s) was completed. The results are now being prepared for publication. For Cu we have also determined the nuclear magnetic moment, in order to be able to extract the isospin impurity in the main decay of 59Cu with sufﬁcient precision. The technique of NMR on oriented nuclei (NMR/ON) was used for this. The resulting resonance curve as a function of frequency, leading to a magnetic moment value of µ = 1.891(9) µN, is shown in Fig. IS381–1. This moment is interesting in itself since 59Cu has only two neutrons more than the closed neutron shell isotope 57Cu. The experimental value is lower than the two theoretical predictions, indicating a strong shell breaking at 56Ni.

69 A new measurement with As (t1/2 = 15.1 min) was also carried out. The activity was implanted into the NICOLE 3He-4He dilution refrigerator at ISOLDE and measured in on-line conditions. The nuclei were cooled to the millikelvin region and polarized using the low-temperature nuclear orientation (LTNO) method. The sample temperature was determined from the anisotropy of a calibrated 57CoFe nuclear orientation thermometer. Beta particles were detected and their asymmetries measured with HPGe detectors mounted inside the 4.2 K radiation shield of the refrigerator and operating at a temperature of about 10 K. Also in this case we had to determine the nuclear magnetic moment in order to be able to extract the isospin impurity in the main decay of 69As with sufﬁcient precision. The results of the measurements with 69As are currently being analysed.

Fig. IS381–1: NMR/ON resonance curve.

Experimental Physics Division 85 IS389

In-beam optical pumping polarization was utilized for beta-NMR experiments on implanted short-lived light nuclei. The main goal was a precision measurement of the electric quadrupole moment of the halo nucleus 11Li with respect to 9Li. This should reveal the small core polarization effect of the two halo neutrons in 11Li on the 9Li core. For this purpose nuclear magnetic resonances of lithium isotopes were measured in different host crystals by the observation of beta-decay asymmetry as a function of the applied radiofrequency. The best resolution of nuclear quadrupole interaction with the electric ﬁeld gradient of a noncubic lattice was obtained in a metallic Zn single crystal. Preliminary measurements with poor statistics had already given an improvement in the accuracy of Q(11Li) by a factor of two, compared with results from 1992 which had shown that Q(11Li) and Q(9Li) were identical to within about 10%.

A new experiment is planned on neutron-rich magnesium isotopes, situated in the ‘island of inversion’ around N = 20 and Z = 12, where for neutrons the f7/2 intruder state enters into the sd shell. This corresponds to a disappearance of the N = 20 neutron shell closure. Measurements of nuclear moments will give detailed information on single-particle wave functions and on deformations of these nuclei. Preparatory tests were performed on beams of 29Mg and 31Mg. The nuclear polarization achieved by optical pumping in the ultraviolet (280 nm) resonance line of Mg+ ions proved to be very promising, giving beta-decay asymmetries up to 6%. Based on these tests the experiment will be started in 2004 with the investigation of suitable host crystals for the measurement of magnetic moments and quadrupole moments.

IS392

Very neutron-rich species far from stability are characterized by a large energy window open to β decay. As a result, their decay is complex, involving branchings over many different channels populated by one or multiple neutron emission and isobaric ﬁliations. Today complete theoretical shell model calculations are possible for heavy calcium isotopes boosting the interest of precise experimental investigations over the whole

Qβ energy window. In the A = 40–56 mass range, when the number of neutrons increases, the f7/2 sub-shell is closed and the interacting orbitals are only f5/2, p3/2 and p1/2. Heavy calcium isotopes, on account of the simplicity of their wave-functions, are the optimal choice to determine precisely the effective nucleon–nucleon interaction which, until now, has strongly diverged between different calculations.

The aim of this experiment is to observe the β decay of 51,52,53K isotopes with an utmost performing neutron and gamma detection. The association of 16 elements of TONNERRE (LPC- Caen) with a set of low neutron energy counters and with two germanium clusters from the MINIBALL array allows efﬁcient coincidence measurements. A 4 π β detector is used to start the neutron time-of-ﬂight measurements and a tape transport system allows one to reduce the build up of daughter activities. The multiparametric data taking is triggered by the PSB proton burst. Each event (β, γ, neutron) is labelled in time. The analysis of the collected data is in progress.

In the nuclei we are dealing with, the Gamow–Teller resonance is located outside of the Qβ window but an important part of it is still accessible by radioactive decay. The lowest lying Gamow–Teller states will be located in 51,52,53Ca and the still unknown properties of natural parity levels will be investigated. The results should precisely indicate the effective n–n interaction in the fp shell as well as the n–p interaction across the sd and fp shells, by comparison with the full shell-model calculations carried out at Strasbourg.

86 Experimental Physics Division IS400

The ﬁrst step towards the experiment was a detailed yield and release study of noble gas isotopes which was carried out during numerous target tests. One result of these tests was the measurement of half-lives and 94-99 144-147 Pn values for the neutron-rich Kr and Xe isotopes. The properties of these isotopes are vital in order to determine the background of the argon beams.

In the summer of 2001 a ﬁrst beam time was spent measuring the properties of very neutron-rich argon nuclei using an MK7 plasma ion-source with a water-cooled line and a β-neutron detector set-up at the new ISOLDE spectroscopy station. In this run we obtained new information (half-lives, Pn-values) on the very exotic neutron-rich 49,50Ar isotopes using 50Ar+ and 49Ar2+ beams. 47,48Ar+ spallation products can not be measured using a β-neutron detection set-up on account of the strong background from 94,96Kr2+ and 141,144Xe3+ ﬁssion product beams.

For the second run (September 2003) we considered an alternative method. The measurement was performed with a doubly charged argon beam utilizing a beta-gamma detector set-up which accommodates the possibility to identify gamma-transitions that originate from the different components of the Ar2+/Kr4+/Xe6+ mixture. This possibility was recently opened up at ISOLDE with the irradiation of targets by fast neutrons produced by proton bombardment of thick metal converters. The argon isotopes, products of proton-induced asymmetric ﬁssion, are not produced in the neutron irradiation of an actinide target. Thus, the comparison of the gamma-spectra collected for the direct proton bombardment of the target with those arising from the use of the neutron converter gives an unambiguous identiﬁcation of the beta-delayed gamma-rays of the argon isotopes (Fig. IS400–1). Detailed information on the 47Ar decay, e.g., proton-hole states in the doubly magic 48Ca nucleus, was obtained in this study.

Fig. IS400–1: Spectra for a doubly charged 47Ar beam, taken for direct proton bombardment (black line) and for neutron irradiation via converter (grey line).

Furthermore, the information on the decay of the 48,49,50Ar isotopes was also extended. The analysis of the data regarding these isotopes is in progress and will be published in the very near future. However, the measurement pertaining to the 48Ar nucleus, which is the most important one for the meteorite anomaly

Experimental Physics Division 87 problem, needs further improvement. The use of a singly charged 48Ar beam is impossible due to strong 96Kr/ 144Xe fission background, whereas use of a doubly charged 48Ar beam significantly reduces the 96Kr/144Xe background, but the beam cannot be mass-separated from the intense singly charged 24Ne beam. This experimental challenge is illustrated in Fig. IS400–2 where the expected implantation rate after proton pulse impact for singly and doubly charged 48Ar beams and corresponding contaminants are presented. The parametrizations of the release curves and in-target production rates are taken from U.C. Bergman et al., Nucl. Instrum. and Meth. B 204 (2003) 220 and the source efficiencies for multiply charged ionization is assumed to be the same as in L. Weissman et al. (submitted for publication). It is clear that the background is overwhelming for both choices of A/q. However, during the experiment we took advantage of the large difference in the Qb-values of 24Ne and 48Ar. In this manner a subclass of 48Ar events could be selected and thus separated from the dominating 24Ne background with the help of a beta telescope. Although this method allowed us to measure the 48Ar half-life, for which the data analysis is still in progress, the conclusion remains that additional improvement of the purity of the 48Ar beam is necessary to reach further.

Fig. IS400–2: The expected injection rate for a singly and a doubly charged 48Ar beam and the corresponding contaminants.

We are currently submitting an addendum to our proposal where we consider finalizing the IS400 experiment and overcoming some experimental challenges by using a novel idea for purification of noble gas beams that has recently become a possibility at ISOLDE. The 48Ar/96Kr/144Xe/ noble-gas cocktail beam will be captured in the ECRIS where, after charge breeding, the different charge-state distributions and the resulting shift in A/q values for the isotopes of the mixed beam, will provide a purified 48Ar beam for the measurement.

IS402

The goal of the MISTRAL experiment is to perform precision measurements of the masses of exotic nuclides produced at CERN’s ISOLDE facility. MISTRAL is especially suited for this task due to its very rapid measurement time that gives access to the shortest-lived (i.e., most exotic) nuclides that can be produced. A radiofrequency modulation of the kinetic energy of ions that transit the spectrometer is used to produce a transmission peak at a high harmonic of the cyclotron frequency, the position of which is compared with that of a calibrant mass to obtain a high-precision measurement.

88 Experimental Physics Division In 2002, we performed a measurement of the very short-lived (8.6 ms) halo nuclide 11Li, whose properties continue to defy description by nuclear theory. Despite serious problems with the HRS, we were still able to reduce the uncertainty of the two-neutron separation energy of this drip line nuclide. In 2003, we made another attempt, this time using the GPS, an isobaric laser-ionized pilot beam of 11Be, and an improved radiofrequency matching system to achieve a factor of four better resolving power. The resulting transmission scan for 11Li is shown in Fig. IS402–1 with the older result inset for comparison.

FWHM prior 14000 11Li scan

transmission spectrum of 11 Li (T1/2 ~ 8 ms)

FWHM = 57000 with new RF system ⇒ accuracy improved by ∼4

Fig. IS402–1: Transmission scans for 11Li recorded in 2003 using a new radiofrequency matching system and the ISOLDE-GPS and (inset) the 2002 result for comparison. In 2002, tremendous beam transport problems with the ISOLDE- HRS were responsible for the weak statistics. Using the ISOLDE-RILIS to create a pilot beam of 11Be, the statistics were almost ten times higher. Moreover, a completely rebuilt RF matching network improved the resolving power by a factor of four. The uncertainties of the new measurements are almost four times better.

450 MISTRAL Kobayashi91 2003 (reaction) 400 (preliminary) Wouters88 (TOFI) 350

300 AME95 (keV) 2n 250 Young93

Li S (reaction)

11 200

150 Thibault75 (mass spec.) 100 Fig. IS402–2: Comparison of two-neutron separation energies determined from different mass measurements of 11Li. The new MISTRAL result, almost four times more accurate than that of Young et al. (1993), is signiﬁcantly higher, indicating a smaller halo radius and preserving the ‘magic’ nature of the N = 8 shell closure.

Experimental Physics Division 89 The analysis of the 2003 experiment (constituting part of the doctoral thesis of C. Bachelet) is practically 11 ﬁnished. A preliminary result for the two-neutron separation energy of Li is shown in Fig. IS402–2. The S2n value indicates 11Li to be more bound than previously thought. This has two important implications for nuclear physics: (1) the halo radius is smaller as a consequence, which is the contrary to what modern nuclear models have predicted; (2) N = 8, one of the ‘magic’ numbers showing exceptional stability, would seem to preserve its magically stable character, contrary to the fashionable tendency for these shell closures to wilt at the drip line.

IS407

With the Resonance Ionization Laser Ion Source at Isolde, isobaric beam contamination is greatly suppressed and previously unavailable, neutron-deficient lead isotopes far from stability have become available for study. Moreover, owing to the inherently large optical isotope shift of 2 GHz/amu in the lead region and a magnetic hyperfine splitting of the order of 10 GHz, it is feasible to use the laser ion source also for direct atomic spectroscopy. Indeed, the first step of the ionization process is sensitive to the isotope shift and the hyperfine structure. Hence the change in the nuclear mean square charge radius and, for non-zero nuclear spin, the magnetic moments can be deduced. If one measures along extended isotopic chains, systematic trends in the nuclear structure can be extracted.

Of particular interest is the extension of our knowledge of charge radii and nuclear moments for the magic lead isotopes across mid-shell at N = 104. Next to the evolution and the role of 0+ intruder states and the phenomenon of shape coexistence, it will allow us to directly test the predictions of various nuclear models.

In order to certify the validity of the in-source laser spectroscopy method, we measured the known isotope shift of 190Pb. Our result of δ 208,190 = 0.839(10) fm2 nicely agrees with the earlier result at GSI of δ 208,190 = 0.840(10) fm2 [S. Dutta et al., Z. Phys. A 341 (1991) 39]. Next the variation of the mean square charge radii was determined for the even isotopes 184,186,188Pb. For the odd isotopes 183,185,187Pb, this quantity was deduced for both the 13/2+ and 3/2– isomeric states and the magnetic moments derived with higher precision than during the preliminary measurements under IS387. An example of a hyperﬁne scan for 185Pb is shown in Fig. IS407–1.

From our experiment, it appears that the ground states of the lead isotopes remain spherical. This should be seen in a context where several 0+ states with different deformations have been observed throughout the neutron-deﬁcient even lead isotopes and triple-shape coexistence at low-excitation energy has been ascertained at midshell for 186Pb [A. Andreyev et al., Nature 405 (2000) 430]. Our measurements ﬁrmly establish that mixing of the deformed 0+ states in the ground state is limited.

90 Experimental Physics Division 1500

1000 I = 13/2

counts 500

0 I = 3/2

17642,8 17643,0 17643,2 17643,4 17643,6 wave number [cm–1] Fig. IS407–1: Hyperﬁne scan of the 13/2 and 3/2 isomeric states in 185Pb as a function of the wavelength of the ﬁrst step laser.

IS410

After a series of experiments aiming to commission the REX accelerator and the MINIBALL HPGe array and to perform ﬁrst physics experiments in 2002, two production runs were carried out in July and October 2003 to study collective and single-particle properties of the neutron-rich Mg isotopes using Coulomb excitation on a natural nickel target and neutron-pickup on a 2H target using the (d,p)-reaction in inverse kinematics. The information extracted from these measurements will give new insights into the rapid changes of nuclear structure in the vincinity of the island of deformation around 32Mg.

The intensity of the 2.25 MeV/u 30Mg beam provided by ISOLDE and the REX accelerator was about 2 × 104 particles per second. For the Coulomb excitation of 30Mg, a 1.0 mg⋅cm–2 natural nickel foil served as the target in the MINIBALL target chamber. The identification of the reaction products and the determination of their energy and direction of flight was accomplished by a silicon telescope consisting of a ~500 µm thick annular double-sided silicon strip detector (dE) and an additional ~500 µm unsegmented silicon detector (E) covering laboratory angles from 16° to 53°. The coincident de-excitation γ rays were detected with the MINIBALL HPGe array (currently consisting of eight triple cluster detectors each comprised of three sixfold- segmented HPGe detectors), set up in the most efficient geometry (efficiency ~10% at Eγ = 1 MeV). Here the interaction point of each γ ray is determined by an online-onboard pulse shape analysis, one of the key features of the MINIBALL array, resulting in approximately 100-fold increase in granularity in comparison with a non-segmented detector. A parallel-plate avalanche counter served as a beam monitor.

A first preliminary analysis of the Coulomb excitation of 30Mg on the nickel target was performed. Besides the excitation of the beam particles, the target nuclei are also Coulomb excited. These two reaction channels can be distinguished kinematically by the energy and scattering angle in the first silicon detector where the heavy reaction products are fully stopped. For the (not yet completely calibrated) Doppler correction the positions of the γ rays are determined by the pulse shape analysis, whereas the energy and direction of flight of

Experimental Physics Division 91 the γ-emitting nuclei can be obtained by a kinematic reconstruction using the information from the segmented silicon detector. A preliminary γ spectrum (containing data taken during about three days) after Doppler correction is shown in Fig. IS410–1. If the Doppler correction is performed for 30Mg the transition of the ﬁrst excited 2+-state in 30Mg at 1482 keV can be seen. When carrying out the Doppler correction for the excited target nuclei, the two gamma lines at 1454 keV and 1333 keV show up in the spectrum resulting from transitions of the ﬁrst excited 2+ states in 58Ni and 60Ni, respectively. As the lifetimes of these two states are ++→ 30 very well known, they can serve as calibration for the extraction of the BE()20; gs 21 value of Mg.

After the energy upgrade of the REX accelerator to an energy of 3.1 MeV/u, the production runs of MINIBALL at REX-ISOLDE will continue in 2004 with several experiments including the second part of IS410: Coulomb excitation of 32Mg.

40 Doppler correction for: 30Mg nat.Ni 35 Ni 30Mg Ebeam = 2.25 MeV/u 4 Ibeam ~ 2*10 /s, T ~ 3 days 30 preliminary

58 25 Ni 30Mg + + 60 2 0 + + Ni gs 2 0gs 20 + + 2 0gs FWHM = 14 keV Counts / 4 keV 15

0 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650

Eγ [keV] Fig. IS410–1: Energy distribution of the emitted γ’s (Doppler corrected).

IS413

The Penning-trap mass-spectrometer facility ISOLTRAP at ISOLDE/CERN looks back on an excellent harvest in 2003. The masses of more than 50 short-lived radionuclides were measured during four runs of a total of 20 radioactive beam shifts. Almost all of the masses were determined with a relative uncertainty in the order of a few 10–8. In 19 cases the accuracy was improved by more than one order of magnitude, in several cases by a factor close to 100. For ten radionuclides the masses were measured for the ﬁrst time. The shortest- lived nuclide addressed was 74Rb with a half-life of only 65 ms.

ISOLTRAP plays a prominent role in mass spectrometry of short-lived radionuclides. Its method is based on the determination of the cyclotron frequencies of ions stored in a homogeneous and stable field of a superconducting magnet. ISOLTRAP consists of three functional parts: a radiofrequency quadrupole (RFQ) ion trap and two Penning traps. The linear gas-filled RFQ ion trap stops the 60 keV continuous ISOLDE beam and prepares it for efficient transfer into the preparation Penning trap. To this end the ISOLDE ions are electrostatically retarded before they enter the RFQ, where they are cooled by energy loss due to helium buffer gas cooling. After an accumulation period (typically 10–20 ms) the ions are transferred as an ion bunch to the tandem Penning trap system. In the preparation Penning trap the ions are stored (up to 1 s) and contaminant ions are removed by resonant radiofrequency (rf)-excitation. The ions are then transferred to the second,

92 Experimental Physics Division precision Penning trap where the mass is measured. The frequency of an azimuthal quadrupolar rf-ﬁeld is scanned for determination of the ions’ cyclotron frequency. The resonance is detected with a time-of- ﬂight technique. The mass m of an ion with charge q is obtained by comparison of its cyclotron frequency ν π c = qB/(2 m) with the cyclotron frequency of a reference ion with known mass. ISOLTRAP reaches a relative mass uncertainty of 1·10–8, a requirement for contributions for tests of the Standard Model like weak interaction studies.

In this report, one specific highlight of 2003 is addressed in detail: By combining selective resonant laser ionization of on-line produced short- lived radionuclides with ISOLTRAP, isomerically pure samples of 68,70Cu were produced and studied for the first time. This is a breakthrough in mass spectrometry and radioactive ion-beam preparation. In combination with β-decay studies, three β- decaying isomers were unambiguously identified in 70Cu. Owing to the different hyperfine structure of the 70Cu isomers (see upper part of Fig. IS413–1), the isomers could be selectively ionized depending on the laser frequency tuning. For the mass measurements of the isomers, the laser frequency was tuned to the positions a, b, and c, respectively, as indicated by arrows. The obtained resonance signals for 70a,b,cCu+ are shown in the bottom part of Fig. IS413–1. While for 70aCu+ and 70bCu+ the selectivity of the RILIS was high enough to almost separate these isomers, in the case of 70cCu+ an additional cleaning of the other isomers was required to obtain a clean spectrum. These data exemplify the strength of this combined technique (RILIS + ISOLTRAP) to produce pure samples of short-lived radioactive nuclei, at present only possible at ISOLDE/CERN. In addition, the new Fig. IS413–1: Top: Intensity of the 101.1 keV mass data show that the literature value for the (circles) and 141.3 keV (triangles) isomeric ground state is off by 226 keV due to a wrong state transitions in coincidence with the associated β- assignment. delayed γ rays as a function of laser frequency. The γ rays associated with the decay of the (6–) For next year mass measurements on, for isomer are shown as squares. Bottom: Time-of- example, the β-decaying nuclides 22Mg, 26mAl, and flight resonance curves of the 70a,b,cCu+ isomers 62Ga as well as their respective daughter nuclides at an excitation time T = 0.9 s for the laser are planned. In addition we would like to address RF frequency settings a, b, and c, as marked with some masses of proton and neutron halo candidates arrows in the upper part. The solid lines are fits like 17Ne. of the expected line shape to the data points.

Experimental Physics Division 93 IS414

The IS414 Collaboration is part of a concentrated effort at ISOLDE to determine the structure of exotic Mg nuclei. 31Mg represents a key nucleus at the border of ‘the island of inversion’ where the shell model conﬁgurations are strongly rearranged. The nucleus of 31Mg is expected to exhibit coexistence of spherical and intruder conﬁgurations, yet the exact nature of the observed excited states has not been determined. Our aim is to obtain new information that would better characterize the excited states in 31Mg.

The second objective of this experiment was to measure with high precision the half-life of the first excited 2+ state in 32Mg. This state is located at only 885 keV, indicating that the ground state in 32Mg is dominated by the intruder configurations. Our measurement would represent an independent verification of the B(E2; 0+ → 2+) values obtained so far in a few studies using Coulomb excitations at intermediate beam energies. These results indicate an enhanced collectivity of the 885 keV E2 transition, yet they show significant discrepancies. The advantage of time-delayed coincidence measurements is that they are free of corrections used in the Coulex studies, which strongly affect the deduced B(E2) results.

The data analysis is in progress, yet a number of new results has already emerged on 30,31,32Mg. In particular new states were identified in 31Mg and 32Mg and a few level lifetimes were measured for the first time in these nuclei. Figures IS514–1 and IS514–2 present preliminary half-life values for the 221 keV level in 31Mg and for the 1789 keV state in 30Mg, respectively. The relatively short lifetime of the 221 keV state implies that the 170 and 221 keV transitions de-exciting this state are not E2 transitions and if they have any E2 admixture it has to be weak. On the other hand, they can be of the E1 or M1 type. If the 170 keV gamma ray is the 3/2– to 1/2+ transition, as proposed in [G. Klotz et al., Phys. Rev. C47 (1993) 2502], then the measured B(E1) is 4.7(4) × 10–4 e2fm2, thus about ten times slower than the predicted B(E1) value of 3.4 × 10–3 e2fm2. On the other hand, the long lifetime of the 1789 keV state in 30Mg represents a puzzle. It would be consistent if this state is the 0+ intruder. However, previous studies report a 1789 keV gamma ray de- exciting this level to the ground state, which negates such an assignment. Our brief measurement of the beta decay of 30Na confirms the presence of the 1789 keV gamma ray, yet the gamma-ray spectrum in coincidence with the 3178-keV transition feeding the 1789 keV level from above, shows very clearly the 306 and 1482 keV peaks but no events at 1789 keV. We take it tentatively as evidence that the 1789 keV gamma ray is placed elsewhere in the decay scheme.

Fig. IS414–1: Time-delayed βγγ(t) spectrum Fig. IS414–2: Same as Fig. IS414–1 but for the showing slope due to the lifetime of the 221 keV 1789 keV state in 30Mg. state in 31Mg. The listed value is preliminary.

94 Experimental Physics Division IS417

This experiment will make a systematic complete coincidence study of beta-delayed particles from the decay of neutron-rich lithium isotopes. The lithium isotopes with A = 9,10,11 have proven to contain a vast amount of information on nuclear structure and especially on the formation of halo nuclei. Halos have caught the interest of nuclear physicists during the last decade. States with a seemingly simple few-body structure situated close to a threshold can develop an unusually large spatial extension. The detailed study of this phenomenon has already given many results as reﬂected in a recent review paper, but questions remain, in particular concerning two-neutron halo systems like 11Li. An essential step is the comparison of beta-strength patterns in 11Li and the core nucleus 9Li, another is the full characterization of the break-up processes following the beta decay. To enable such a measurement of the full decay process we are using a highly segmented detection system where energy and emission angles of both charged and neutral particles are detected in coincidence and with high efﬁciency and accuracy.

The β-transitions from 11Li that directly involve 20.6 11Li 3/2– ? the halo neutrons are most likely to be 0.35 t =8.2 ms 17.9 1/2 concentrated at the highest excitation energies 18.1 9Li + d 0.01 that can be reached experimentally. However, it is 15.7 8Li + t not known whether these transitions will take ? place through excited states in 11Be (see Fig. IS417–1), as would be the case for a normal β− β-decay, or occur directly to continuum states, as appears to be the case for the β-delayed deuteron 10.59 α+α+3n branch. In the ﬁrst case the resonances fed in 0.08 11 α+6He+n 8.9 Be would be able to decay by emission of 0.07 7.91 <0.03 7.32 several particles but the decay mechanism in this 9 Be+2n step is also unknown at present. Our experience from the studies of 9C, 12B and 12N is that

+ 0.15 2 coincident detection of all emitted particles 3.368 makes it possible to answer such questions in an unambiguous way.

+ <0.002 0 0.503 10Be+n The known open channels in the 11Li decay are n- 11Be 10Be, 2n-9Be, 3n-2α, n-6He-α, t-8Li and d-9Li. Fig. IS417–1: Schematic diagram of the β-delayed Hence the ideal setup should be able to measure particle emission from 11Li. At the right threshold in 4 π, the charged particles with particle values in MeV relative to 11Be are shown. At the identiﬁcation (PID) as well as the neutrons and left, observed branching ratios given in per cent. all in coincidence.

The extracted beam of 9,11Li ions from ISOLDE is implanted into a thin carbon foil at the centre of a cubic support structure (10 × 10 × 10 cm3) containing charged-particle detectors on each side. The cube is surrounded by β-detectors for the n-ToF signal. A neutron detector array is placed at 1.2 m distance from the collection point outside the vacuum chamber. The charged-particle detectors used are of a new kind of double- sided Si strip detectors (DSSSD) developed by us in collaboration with MICRON Semiconductor Ltd. The new design with a very thin deadlayer (100 nm) allows for charged particles to be detected down to ~100 keV

Experimental Physics Division 95 energy with high granularity. With a Si thickness of only 60 µm the beta-response in these detectors is negligible. For the neutrons we use the TONNERRE array from LPC-CAEN. TONNERRE combines 18 scintillator elements of 160 cm length, 20 cm width and 4 cm thickness with a 120 cm radius curvature, viewed at both ends by photomultiplier tubes. The array (Fig. IS417–2) has a large acceptance (as installed at ISOLDE up to 25% of 4 π), with an energy resolution of ~10% for neutrons up to 5 MeV and a high overall efﬁciency of 15%. The low energy threshold is at about 300 keV.

The experiment is still taking data, however, parts of the result from the ﬁrst run in June 2003 can be found in Y. Prezado et al., Phys. Lett. B576 (2003) 55.

Fig. IS417–2: The collection spot is in the centre of a cubic construction with 10 cm sides where each face is covered by a DSSSD telescope (inset).

IS423

The INTC-P-172 proposal, envisaging a Coulomb excitation experiment with the 88Kr beam, was accepted by the CERN Research Board on 13/11/2003, after a positive recommendation from the Isolde – Neutron Time of Flight Committee. A total number of 24 shifts out of 32 requested were granted and the number IS423 was ascribed to the project.

The experiment is planned to involve the ISOLDE primary target assembly and magnetic separator to supply the high-intensity radioactive 88Kr beam to the REX post-accelerator. After acceleration to 2.2 MeV/A (ﬁrst run on a light target) and 3.1 MeV/A (another run on a heavy target) it is planned to observe Coulomb excitation of the beam using particle-gamma coincidence events in the CD detector (scattered beam detection) and MINIBALL array (gamma energy measurement).

The same set-up was used by the IS405 experiment – Coulomb excitation of the radioactive 2.2 MeV/A 70Se beam, scheduled for the period 1–8/11/2003. On account of technical problems with obtaining the pure 70Se beam it was decided to give four shifts of the beamtime to the NICOLE group and prepare another target on the GPS frontend (uranium carbide target with a cooled transfer line) which could deliver clean and high- intensity 88Kr beam. This allowed us to perform the ﬁrst on-beam test for the IS423 experiment.

96 Experimental Physics Division The 88Kr beam was intense enough to observe the ﬁrst excited state de-excitation γ-rays. However, due to non-optimal experimental conditions (this mostly means the target, which was optimized for 70Se, not the 88Kr case) the expected number of counts in the interesting γ line, de-exciting the supposed Mixed Symmetry state, is estimated to be 1–2, far below any experimental sensitivity limit. Figure IS423–1 shows the collected γ energy spectrum with the ﬁrst excited state line at 776 keV clearly visible.

Since it is planned to use another target for the low-energy part of the experiment, the collected data cannot be combined with future measurement of the Mixed Symmetry state. However, the time used gave us valuable experience concerning set-up efﬁciency measurements, background estimation, and checking the assumptions about the 88Kr Coulomb excitation cross-section.

The performed run lasted for about 8 shifts and this number was subtracted from the 24 shifts originally granted leaving half of the requested time (16 shifts out of 32) for the main measurement. After careful analysis of the data acquired, we shall probably ask the INTC for more time to allow successful measurement of the Mixed Symmetry state of the 88Kr nucleus.

100

0 200 400 600 800 1000 1200 1400 1600 1800 2000 Fig. IS423–1: Gamma-ray energy spectrum after Coulomb excitation of the post- accelerated 88Kr beam.

Solid-State Physics

IS359

The experiment was completed in 2003; the last beam time was devoted to studies of the diffusivity of ≤ ≤ 57 interstitial Fei in SiC and Si1-xGex alloys (0 x 1) by means of Fe emission Mössbauer spectroscopy. 57 + 12 2 Radioactive Mn ions (T1/2 = 1.5 min) were implanted with 60 keV energy to ﬂuences <10 /cm into single crystals held at temperatures of T = 300–1050 K. The annealing of the radiation damage from the 57 ≤ ≤ implantation during the lifetime of the Mn probe atoms for T > 450 K in Si1-xGex (0 x 0.1) leads to their incorporation on substitutional lattice sites. In the subsequent β–-decay of 57Mn to the 14 keV Mössbauer state 57m of Fe (T1/2 = 100 ns) an average recoil energy of 40 keV is imparted to the daughter nucleus, which expels a sizeable fraction of the Fe atoms into tetrahedral interstitial sites. A few diffusional jumps of these interstitial γ Fei atoms during the lifetime of the Mössbauer state led to a line broadening of the emitted Mössbauer -

Experimental Physics Division 97 radiation, which is directly proportional to the jump frequency. For a random interstitial diffusion mechanism 0/+ as in pure silicon the jump frequency is directly proportional to the diffusivity; thus determined Fei diffusivities in its two different charges are found to be in reasonable agreement with macroscopic diffusion ≤ ≤ results. In Si1-xGex alloys for 0.02 x 0.08 the preliminary results show an increasing jump frequency of interstitial Fe with increasing Ge concentration, whereas the macroscopic diffusivity is known to be unaffected up to x ≤ 0.08. These apparently contradictory results can be accommodated in a model considering a locally increased jump frequency for interstitial Fe when a Ge atom is present among its nearest or next-nearest neighbour atoms, i.e. in the hexagonal interstitial saddle point conﬁguration. For sufﬁciently low Ge concentrations this would not affect the macroscopic diffusivity appreciably. Further experiments are planned for higher Ge concentrations.

In silicon and Si1-xGex (x < 0.1) multiple diffusional jumps of interstitial Fei lead eventually to the formation of a meta-stable Fei-V pair with the vacancy created in the recoil event. FP-LMTO calculations of the total energy and the Fe hyperfine interactions for the pair configuration show the Fei atom at a shorter distance from the vacancy than for a tetrahedral interstitial site and yield good agreement with the measured hyperfine parameters. The formation enthalpy of the process is consistent with the diffusion enthalpies for 0/+ Fei and is incompatible with the much smaller diffusion enthalpies known for (differently charged) vacancies at lower temperature. This clearly indicates a temperature-dependent increase of the vacancy diffusion enthalpy, i.e. a change in its nature in silicon. These findings are in contrast with the formation of meta-stable Fei-V pairs in germanium at much lower temperatures in analogous experiments, consistent with the known vacancy diffusion enthalpy.

In SiC only partial annealing of the implantation damage is observed up to the highest temperatures and a corresponding increase of the substitutional fraction occurs only for T > 750 K. Below that temperature a fraction, assigned to interstitial Fe surrounded by C nearest neighbour atoms, increases upon damage annealing. A second interstitial fraction, assigned to interstitial Fe with Si nearest neighbours, anneals completely at T = 700–900 K by conversion into the C-surrounded interstitial fraction. This ﬁnding suggests a single diffusional jump process of interstitial Fe from the Si-surrounded to the more stable C-surrounded interstitial conﬁguration.

IS368

The electrical and optical properties of semiconductors are considerably inﬂuenced by the presence of impurities. For a basic understanding of the electrical or optical dopant properties of particular elements, it is essential to know the lattice sites that the impurities occupy within the semiconductor crystal. Experiment IS368 aims at lattice location studies of the transition metals Fe, Cu and Ag and of various rare earth (RE) elements in semiconductors by means of the electron emission channelling technique. This lattice location method applies radioactive isotopes which decay by the emission of electrons (β– particles or conversion electrons) and which are produced and implanted into single-crystalline semiconductor samples at CERN’s ISOLDE facility. On their way out of the crystal the electrons experience channelling or blocking effects along low-index crystal directions. This leads to an anisotropic particle emission yield from the crystal surface which depends in a characteristic way on the lattice sites occupied by the emitter atoms. Electron emission channelling patterns are recorded by means of position-sensitive Si pad detectors which were developed at CERN. Recently, the 2nd addendum for IS368 was approved by the INTC committee and a detailed progress report until mid 2003 is included in this addendum, which is available on the CERN document server (CERN/ INTC 2003-037).

98 Experimental Physics Division In 2003 we intensified our lattice location experiments on 67Cu in the hexagonal wide-bandgap semiconductor ZnO by investigating the Cu lattice sites as a function of implanted dose. The emission channelling effects from 67Cu were measured in the as-implanted state and following annealing up to 800°C under vacuum. In samples implanted with doses from 2 × 1013 cm–2 to 1 × 1014 cm–2 we clearly identified two different configurations of Cu. In the as-implanted state and following annealing up to 200°C, the majority of Cu atoms (~70%) were found on almost ideal substitutional Zn sites (SZn), characterized by small root 67 mean square (r.m.s.) displacements u1( Cu) around 0.16-0.20 Å. However, this configuration of Cu showed low thermal stability, and annealing at 400°C started the conversion of Cu from SZn sites to Zn sites with large r.m.s. displacements, of the order of 0.35-0.53 Å. Finally, annealing at 800°C in vacuum lead to partial Cu outdiffusion. In contrast, in a sample implanted with a lower dose (4 × 1012 cm–2), the conversion of Cu to displaced substitutional Zn sites was nearly absent. The fact that the formation of displaced substitutional Cu is enhanced in samples implanted with higher doses points towards the formation of Cu-pairs or a pronounced reaction of Cu with crystal defects such as vacancies or interstitials that result from the implantation.

We have also continued our emission channelling experiments with rare earths in GaN, a system of interest for possible applications in optoelectronics. The lattice location of Er was determined in pure GaN and GaN pre-implanted with O or C, respectively. The conversion electrons emitted by the probe isotope 167mEr gave direct evidence that the majority (≈90%) of Er atoms were located on substitutional Ga sites in all samples. Annealing did not change these fractions, although the Er r.m.s. displacements decreased for annealing up to 900°C. The only visible effect of oxygen or carbon doping was a slight increase in the r.m.s. displacements with respect to the undoped sample. Our ﬁndings therefore show that co-implanting Er with O or C into GaN does not signiﬁcantly affect the incorporation of Er into Ga sites. This means that differences in the luminescence behaviour of Er in GaN, which were observed following co-implantation of Er with O or C and have been reported in the literature, cannot be attributed to a change in the lattice location of Er, unlike in the case of Er in Si. Besides Er we have also studied the lattice location of 153Sm and 155Eu in GaN, and of 147Nd in AlN. In all these cases we found the RE atoms on substitutional cation sites, i.e. replacing Ga or Al atoms, respectively.

IS369

The IS369 experiment, a collaboration between the Universität des Saarlandes, the Universität Konstanz, and the ISOLDE group, uses radioactive probes delivered by the ISOLDE facility for the investigation of II-VI semiconductors. The radioactive isotopes are employed simultaneously as probe atoms and as dopant atoms for optimizing the electrical and optical properties of II-VI semiconductors. In 2003 within the IS369 experiment, the isotope 155Tb was used for PAC investigations in ZnO (155Tb) and in Cd, and the isotopes 67Cu and 111Ag were used for tracer-diffusion experiments in CdTe. These isotopes were delivered during four beam periods.

In May and July 2003, the UC2 target, operated with laser extraction (LIS), supplied 67Cu and 111Ag, respectively. Both isotopes were used for diffusion experiments in CdTe. For Ag and Cu completely unexpected diffusion proﬁles were observed after implantation and a subsequent thermal treatment. The shape and the range of the proﬁles depend strongly on the external conditions during thermal treatment and on the pre-treatment of the CdTe crystal. The experiments established the new and unexpected diffusion properties of the dopants Ag and Cu in CdTe and continued the work of 2002.

Experimental Physics Division 99 In the second beam period in May 2003, a Ta-W-surface source was used for extracting and implanting 155Tb into ZnO and Cd. The subject of interest was the incorporation sites of 155Tb atoms into the lattice of ZnO, since ZnO:Tb is a potential phosphor material. In order to explore the possibilities of 155Tb for its potential application as a new PAC probe for solid-state science, 155Tb atoms were implanted in Cd metal.

In 2003, experimental developments and experiments concerning both IS369 and IS401 were performed.

For photoluminescence (PL) investigations with short-lived isotopes (t1/2 < 1 d) that are especially isotopes of light elements, a PL apparatus with funding from the German federal ministry of science (BMBF) was set up next to the ISOLDE hall. In order to enable PL investigations on an as wide as possible spectrum of semiconductor materials, different lasers, such as a HeCd – and a Nd:YAG laser, can be used. In a He bath cryostat, the sample temperature can be varied from 1.5 K up to ambient temperature. The detection of the luminescence radiation occurs after the analysis in a 0.75 m monochromator with a CCD camera or a Ge diode. In a ﬁrst experiment, the so-called green band in ZnO was investigated. Its origin is discussed in the literature controversially.

In general, during the last few years the availability of suitable radioactive isotopes has contributed to an improved understanding of the behaviour of dopant atoms in II-VI semiconductors. The availability of numerous radioactive isotopes, suitable for PAC, PL, and tracer-diffusion experiments, is an important prerequisite for ﬂexible and successful investigations towards an optimization of the electrical and optical properties of II-VI semiconductors.

IS375

It is well known that Pd, grown in a few monolayers (ML) on Ni, exhibits a R(t) a.u. 0.10 (static) ferromagnetic order. Furthermore it was shown that ferromagnetic A 0.06 0.05 T = 300 K ultra-thin Ni on a single crystal of Pd induces dynamic magnetic interactions

0.00 0.04 in Pd, e.g., 7 ML away from the interface. But so far, what happens exactly

–0.05 at the Ni/Pd interface in Pd has not been studied. 0.02 –0.10 Pd(111) 0.00 Figure IS375–1 presents the results of this investigation. Part (A) shows the PAC spectrum of the electric quadrupole interaction frequency (0.38 Grad/s) 0.00 T = 273 K 111 111 0.02 when the PAC probe In/ Cd is incorporated in the topmost layer of a single crystal of uncovered Pd(111) (noncubic environment). In part B, Pd is –0.05 B 1 ML Ni 0.01 partially covered by one ML Ni, which is not ferromagnetic at 273 K. An –0.10 additional considerably smaller interaction frequency (0.05 Grad/s) (light Pd(111) 0.00 grey colour in the Fourier transforms) arising from the EFG for Cd at the Ni/ Pd interface is observed. This part of the experiment demonstrates that the 0.00 111In probes remain in the topmost layer of Pd. Moving into the Ni layer, 0.02 –0.05 C T = 83 K they would exhibit an even larger frequency (0.45 Grad/s), which is not 5 ML Ni observed. –0.10 111 111 Pd(111) Fig. IS375–1: PAC time spectra of In/ Cd at the positions, shown –0.15 0.00 0 100 0.0 0.2 0.4 schematically in the insets. The colours of the frequencies in the Fourier Time [ns] Grad/s transforms correspond to the colours of the probes. In the middle and lower part the uncovered fraction (black) serves for monitoring.

100 Experimental Physics Division No frequency change occurs when Pd is covered by 5 ML of ferromagnetic Ni, (part C). Cadmium in Pd, although in contact with ferromagnetic Ni, shows no static magnetic interactions, in contrast with the experiment with ultra-thin Pd on Ni. We conclude that the above-mentioned dynamic interactions in Pd are also present exactly at the Ni/Pd interface.

Such results with monolayer resolution in buried layers demonstrate the power of nuclear methods.

IS390

The IS390 Collaboration performs local studies on relevant structural problems of colossal magnetoresistive oxides (manganites) by doping these with suitable radioactive isotopes for perturbed angular correlations and emission channelling. The measurement of electric field gradients on insulator and conducting samples provides information on the coupling between the local structure and chemical doping (by oxygen and metal vacancies), magnetic and electric properties. The hyperfine magnetic field is also useful for probing magnetic ordering of Mn ions. The main issue addressed was the characterization of local deformations in manganites, due to polaronic mechanisms, using appropriate radioactive ions, to study the effects of charge ordering and phase separation at a local scale. The modifications of the crystal field parameters along the series Pr1-xCaxMnO3 were studied in detail (Fig. IS390–1a, data at room temperature). The charge order transition in x = 0.35 sample near T = 220 K produces a very sharp modification of the normalized EFG principal component (Vzz), shown in Fig. IS390–1b. Other studies include the structural transitions on the simpler (oxygen doped) manganites LaMnO3+d, concerning their structural and magnetic transitions. An important issue is also the education and training of new Ph.D. and diploma students. At ISOLDE, these new students have been learning nuclear solid-state techniques on the separator, and also participating in another experiment, IS360, which applies similar techniques. A set-up for electrical measurements in the temperature range 10–350 K is under installation. Outside CERN, we have worked on sample preparation and characterization.

2 76 1,00 ) Å 72 (V/

zz 68 0,95 V 2

64 – ) Å 60 0,90 0.66 (V/ zz V 0.60 0,85

η 0.54 0,80 0.48

0.42 100 150 200 250 300 350 400 450 500 550 0.0 0.2 0.4 0.6 0.8 1.0 T(K) x(Ca) Fig. IS390–1: (a) Composition dependence of the crystal ﬁeld parameters in the

series Pr1-xCaxMnO3. Charge ordering occurs, at low temperatures, in the interval 0.3 < x < 0.9. (b) Modiﬁcation of the crystal ﬁeld parameters near the

charge-ordering transition in Pr0.65Ca0.35MnO3. Near the peak, the temperature interval between points is 2 K.

Experimental Physics Division 101 IS396

Within the scope of the investigation of magnetic semiconductors and more generally of magnetic materials by hyperﬁne interactions (PAC method), we found a cubic defect for 111In(111Cd) probes implanted into α-iron. The 111In implantation was carried out at ISOLDE with an energy of 50 keV.

In the case of 111In(111Cd) implanted into nickel such a cubic defect was detected 30 years ago. Its structure has been a point of controversy up to now. Because of the cubic point symmetry of this defect only interstitially positioned 111In probes at sites with tetrahedral or octahedral environments in the fcc Ni lattice can be the reason for such a result. The octahedral site could be excluded by channelling experiments. If one considers the large volume of an In atom as compared to that of a Fe atom a simple tetrahedral In interstitial seems to be unlikely. Therefore a model with the same In position but four tetrahedrally coordinated vacancies as next neighbours is also under discussion.

We performed an analogous experiment with α-Fe instead of Ni and found for the as-implanted samples a large fraction of probes with a magnetic hyperﬁne ﬁeld of Bhf1 = –38.2(4) T at R.T. This value is well known for substituted Cd atoms in a-Fe. 111Cd is the successor of 111In. A small damping points to defects (e.g. vacancies) not correlated with the probes. After a thermal treatment for 10 min. at 500°C (773 K) in vacuum, we observed three different probe surroundings: (i) for substituted Cd-probes (Bhf1 = –38.4(6) T); (ii) Cd probes with a pure magnetic interaction and Bhf2 = +11.5(2) T at R.T.; and (iii) probes with a broadly distributed electric quadrupole interaction (Fig. IS396–1). Measurements with the sign-sensitive ±135° geometry show only the two sharp peaks for Bhf1 and Bhf2 which points to two different pure magnetic probe environments (cubic point symmetry) and one with a dominating quadrupole interaction, which is invisible in this geometry.

6 –0.1

4 ) ω F( R(t)

0.0 2

0 50 100 150 0 500 1000 1500 2000 t [ns] ω [Mrad/s] Fig. IS396–1: PAC spectrum R(T) and Fourier transform F(ω) for 111In(111Cd) implanted α-Fe after heating for 10 min at 500°C. The measurement was made with 90°/180° geometry and a transversal magnetic polarizing ﬁeld of 0.5 T. The dark grey peak (at ω ~1100 Mrad/s) corresponds to substituted probes, the grey one (at ω ~300 Mrad/s) to cubic defects. The part of probes with a dominating quadrupole interaction (broad frequency distribution) is marked in light grey (at ω ~200 Mrad/s).

102 Experimental Physics Division For fcc Ni the octahedral and tetrahedral interstitials possess a perfect cubic point symmetry. This is not the case for bcc α-Fe. But in this case the tetrahedral interstitial position has an exact tetrahedral environment of next neighbours at least and therefore a very weak quadrupole interaction. This means octahedral positions can be excluded for the ﬁeld Bhf2. A decision between a defect model with or without the participation of vacancies is not possible. We hope that WIEN calculations can solve this problem later.

IS401

The IS401 Collaboration (Konstanz, Jena, Dublin, Dresden, Saarbrücken, CERN) is studying defects in elementary semiconductors (Si, Ge) and compound semiconductors (i.e. GaN, GaAs, SiC, ZnO, CdTe) using radioactive isotopes provided by ISOLDE. Electronic properties of semiconductors are extremely sensitive to defects and impurities that have localized electronic states with energy levels in the band gap of the semiconductor. Spectroscopic techniques used in semiconductor physics like photoluminescence (PL), deep level transient spectroscopy (DLTS), or Hall effect, that are able to detect and characterize band gap states do not reveal direct information about their microscopic origin. To overcome this chemical ‘blindness’ of the electrical and optical methods the present approach is to use long-lived radioactive isotopes as a tracer. To enable the use of isotopes with half-lives down to about 1 h, the PL, DLTS, and Hall effect measurement have to be performed ‘on site’ in a laboratory near the ISOLDE hall. For this purpose, a ‘Solid-State Physics Lab’ is being set up near ISOLDE. A state-of-the-art PL spectrometer has been installed at CERN. The following experiments using this lab are planned or already taking data:

– Hydrogen and lithium interaction with gold and platinum in silicon

– Identiﬁcation of transition metal defects in silicon

– Identiﬁcation of acceptor and donor states in GaN

– Creation and identiﬁcation of anti-site defects in GaAs and GaN

– Alkali and alkaline earth defects in Si and Ge

– Identiﬁcation of acceptor states in II-VI semiconductors

– Identiﬁcation of donor and acceptor centres in ZnO

– Deep states of group III acceptors in SiC

ZnO has a direct band gap of 3.5 eV similar to GaN. In contrast with GaN which can only be produced by epitaxial procedures, bulk ZnO crystals of good quality can now be produced, but ZnO is still one of the most poorly understood materials with respect to impurities, defects, and associated energy levels. One such level is the so-called ‘green band’, whose origin is controversial in the literature. Among other possibilities, a Cu 64 → 64 64 defect or vacancies have been proposed. In order to clarify this question, the isotopes Cu Ni/ Zn (t1/ 65 → 65 2 = 12.7 h) and Ni Cu (t1/2 = 2.5 h) were implanted in ZnO and investigated with PL spectroscopy. Surprisingly both experiments show that the intensity of the green band increases with time (Fig. IS401–1) corresponding to the half-life of the implanted isotope (insert in Fig. IS401–1), therefore Cu or Ni as the origin of the green band can be excluded. During the β-decay of both isotopes, a recoil with an energy of more than 24 eV is transferred onto the daughter isotopes. This energy is large enough to displace a Zn atom in the ZnO crystal lattice and to create recoil-induced intrinsic defects. Therefore, these experiments suggest that the green band in ZnO is related to intrinsic defects, like Zn vacancies.

Experimental Physics Division 103 Fig. IS401–1: Photoluminescence spectra of ZnO implanted with 64Cu measured between 3 h and 72 h after the doping. The insert shows the increase of the ‘green band’ intensity with time (T. Agne et al.).

Biological

IS422

111m 199m 204m The short-lived nuclear probes Cd (t1/2 = 49 min), Hg (t1/2 = 43 min), and Pb (t1/2 = 43 min) supplied by the on-line mass separator ISOLDE are used to study the interaction of metals with biological macromolecules such as DNA and proteins. The structure and dynamics of metal sites in biomolecules are important in determining the functional efﬁciency of these macromolecules. Many life processes are based on such interactions. In order to study those metal sites under close-to-physiological conditions, a highly sensitive spectroscopic method is required, like Time Differential Perturbed Angular Correlation (TDPAC). Here, a radioactive atom is placed at the site of interest and by correlating the emitted γ-quanta in space and on a nanosecond time-scale local structural information is provided via the Nuclear Quadrupole Interaction (NQI). These investigations will allow a deeper insight into the adaptivity and rigidity of metal sites in blue copper proteins (electron transfer proteins), into heavy metal detoxiﬁcation processes, into the binding of heavy metal ions to metallothioneines or metal-sensitive genetic switches, and also into the development of heavy metal sensors based on DNA molecules.

In an early effort in the 1970s the nuclear quadrupole interaction of the isomeric TDPAC isotope204mPb was investigated in a variety of metals and compounds. However, in some cases only a rough estimate of the NQIs in these compounds was possible because of the poor statistical quality of the data and serious limitations of the data analysis. In 2002, we could produce this isotope for the ﬁrst time at the on-line isotope separator ISOLDE at CERN and determined the NQI of 204mPb in cadmium metal which was a factor of 2 different from a previous TDPAC experiment. In 2003, we extended our investigations to Pb(II) complexes which were precipitated from aqueous solutions. These Pb(II) complexes will serve as model compounds for the structural investigations of biological macromolecules, the ﬁnal goal of these investigations. Whereas the

104 Experimental Physics Division TDPAC probes 111mCd and 199mHg are predominantly used for studying proteins, the 204mPb TDPAC probe can also be used for investigating nuclear acids, like DNA. Owing to their high sensitivity to ﬂuorescence activity these biomolecules might serve as metal sensors. The ﬁrst TDPAC experiments with DNA are quite promising.

Technical Developments and Experiments in Preparation

IS419

The goal of the IS419 experiment is to measure production cross-sections of gas and volatile elements in a Pb/Bi target. Such data are of great interest in the frame of research on accelerator driven systems, one example being the pilot experiment MEGAPIE at PSI. In the design and construction of such systems it is important to evaluate the amount and type of gas and volatile elements that will be produced, in order to ensure a reliable and safe operation of the experiment. Both stable (1,2H, 3,4He and other noble gases) and radioactive isotopes are of interest. For a correct estimation of the production cross-sections, a measurement with a liquid Pb/Bi target and a proton beam of energy close to that of MEGAPIE (575 MeV) is necessary.

During an exploratory measurement in late 2002 with a standard liquid Pb target the release functions for noble gases isotopes were measured. The results were very promising and showed the feasibility of the experiment; however, the data acquisition system had to be adapted to synchronize the start of the acquisition of the Faraday cup signals with the trigger signal from the pulsed proton beam.

In 2003 a PC-based data-acquisition system with this capability was developed. The new system was successfully tested at ISOLDE during a short measurement with a liquid Pb target at the GPS. Work is currently being performed to add the option of ﬁltering the signals for reduction of noise, which was observed during the test. The measurements using a molten Pb/Bi target will be carried out in 2004.

P111

The WITCH experiment (Weak Interaction Trap for CHarged particles) is being set up foremost to study the electroweak interaction by determining the β–ν angular correlation in the β-decay of exotic nuclei by measuring the shape of the energy spectrum of the recoil ions. At ﬁrst the experiment will focus on pure Fermi decays, which will allow one to search for an additional scalar component in the weak interaction.

The main parts of WITCH are two Penning traps and a retardation spectrometer. Ions are trapped and cooled in the first Penning trap and then transferred to the second trap, also called decay trap. Recoil ions resulting from β-decays in this decay trap are guided by a 9 T magnetic field into the retardation spectrometer (placed in a 0.1 T magnetic field) where their energy is analysed. Since the ion cloud in the decay trap is in vacuum and owing to the cylindrical structure of the trap, the recoiling daughter ions can leave the ion cloud and the trap potential without any significant energy loss or scattering. This will be the first time the energy spectrum of recoil ions from β-decay can be measured for a wide variety of isotopes, independent of their specific properties.

Experimental Physics Division 105 The installation of the WITCH set-up at ISOLDE is now nearing completion. The Detector horizontal beam line that connects the WITCH set-up to the REXTRAP Penning trap and buncher is fully operational. The vertical beam line, which houses a pulsed Retardation drift tube and electrodes to slow down the spectrometer 60 keV pulsed ion beam from REXTRAP before it is injected in the cooler Penning trap, is presently being commissioned. The decay trap cryostat with two superconducting magnets (a 9 T magnet to house the two Penning traps and a 0.2 T magnet in which the cooler trap retardation spectrometer will be installed) has been operational for more than one year. The retardation spectrometer and the micro- PS-booster vertical beamline channel plate detector for the recoil ions, p which is still being tested, will be installed early in 2004. As soon as the commissioning of the vertical beam line is ISOLDE REXTRAP horizontal ﬁnished, the injection of the decelerated beamline beam into the cooler trap will be optimized. Fig. P111–1: Schematic of the This will be followed by a series of tests to WITCH set-up. optimize the manipulation of ions in the two Penning traps. First tests with radioactive ions and a ﬁrst recoil ion spectrum shape measurement are planned for summer and autumn 2004.

REX-ISOLDE

In 2003 beam experiments ran at REX-ISOLDE for seven weeks. Approximately the same amount of time was needed for tests and optimization of the machine, so in total the time of operation of REX in 2003 was about three months.

The nuclear physics experiments were performed – as in 2002 – on the neutron-rich side at final energies of the radioactive ions between 2.2 and 2.3 MeV/u, using the MINIBALL detector for γ-spectroscopy and the Second Beamline for measurements with other detectors. After problems with the beam quality at the target during a first MINIBALL 30Mg run in July, an additional commissioning beam time of the Linac was necessary. In August/September MCP beam monitors at the target position of the two REX beamlines were used for optimization of the spot size at the target. After this optimization procedure the experiments on Coulomb excitation of 74,76Zn (IS412) and of 30Mg (IS410) could benefit from a significantly reduced background and produced very good results.

106 Experimental Physics Division The 30Mg run in particular was a full success. After a preliminary analysis of the Coulomb excitation of 30Mg there is strong evidence that the B(E2) value is about a factor of two smaller than previously reported. This might imply that measurements at intermediate energies (>30 MeV/u) are not as accurate as previously thought. If conﬁrmed, this could be explained by Coulomb-nuclear interference effects not considered properly in the analysis of these experiments or by unobserved feeding from higher lying states. As a classical advantage of the ISOL method, at REX both of these uncertainties are not present or strongly suppressed.

The following lithium run (IS376, IS371, IS399) at the end of October suffered from a sparking extraction electrode of the REXEBIS and later on from problems with the rf ampliﬁer of the second 7-gap resonator. The scheduled measurement time of one week was thus reduced to one day at a too low count rate. The measurements will be partially redone in the beamtime period 2004.

The ﬁnal experiment in 2003 was a test for the acceleration of 70Se (IS405). The beamtime was switched to measurement of 88Kr when it became clear that the 70Se, which arrives at REXTRAP as a SeCO molecular beam, could not pass the trap without break-up at the injection. After ﬁrst analysis the Kr measurement shows promising results. The charge breeding of the Se – and of molecular beams in general – will be investigated in detail in 2004 for future experiments.

In parallel to the running experiments in 2003 an additional accelerator was installed in the REX beamline behind the existing 7-gap resonators. It is a 9-gap IH resonator, which will raise the final energy at REX from 2.3 to 3.0 MeV/u. The amplifier was installed at the end of 2003 and the whole system will be fully operational for the first experiments in mid May 2004.

Recognized Experiments

CAST

Axions can be produced in the sun’s core through the scattering of thermal photons in the Coulomb field of electric charges (Primakoff effect). In a transverse magnetic field the Primakoff effect can work in reverse, coherently converting the solar axions back into X-ray photons of a few keV. The conversion efficiency increases with (B⋅L)2. In the CAST experiment, an LHC prototype dipole magnet (B = 9 T and L = 10 m) with straight beam pipes provides a conversion efficiency exceeding that of the two earlier solar axion telescopes, Brookhaven (1990) and Tokyo (2000), by almost a factor 100. This magnet is mounted on a moving platform and coupled to both gaseous and solid-state low-background X-ray detectors on either end allowing it to observe the sun for nearly 1.5 hours at both sunrise and sunset. The rest of the day is devoted to background measurement and, because of the Earth’s motion, to observations of a large portion of sky. CAST also uses an X-ray mirror system from the German space programme; the converted X-rays will be focused to a ~1.5 mm spot, improving the signal-to-noise ratio significantly over the original CAST proposal and the previous solar axion experiments.

After the first preliminary data taken at the end of 2002, CAST has been fully in a data taking phase since May 2003. While the analysis of these data is still on course in order to fine-tune the experiment performance to face the 2004 operation, a first result has already been obtained after the complete analysis of an important

Experimental Physics Division 107 portion of the 2003 data, including ~60 effective hours of tracking and ~30 days of background taken with the TPC detector. The exclusion obtained (Fig. CAST–1) reaches a value for the axion photon coupling × –10 –1 ga < 1.27 10 GeV in the low mass (coherence in vacuum) region, already a factor 5 in ga better than the previous experiment and approaching for the ﬁrst time the limit dictated by astrophysical considerations.

CAST will continue its data taking during 2004, in order to further improve its sensitivity to solar axions, going deeper into not yet excluded axion parameter space. In addition, the second phase of the experiment is being prepared, with the goal of looking for the converted axions with the magnet pipes ﬁlled with a buffer gas. This will extend the experiment’s sensitivity to higher axion masses. Within this phase, CAST will enter into some regions which are specially motivated by theoretical considerations, leaving room for possible surprises.

Fig. CAST–1: CAST sensitivity to ga.

R&D Projects

RD18 – Crystal Clear Collaboration

The core activity of the Crystal Clear Collaboration is the generic development of technologies to be used in future crystal-based detectors for high-energy physics, medical imaging, and industrial applications. During recent years the development of gamma-ray detectors for biomedical imaging applications, and in particular for Positron Emission Tomography (PET) scanners, has become the main focus. This includes the development of scintillating materials, photodetectors, readout electronics, optical and mechanical assemblies, and software.

Until recently the resolution of available PET scanners limited analyses to relatively large subjects like humans or large animals. Now the PET scanner resolution has improved to the point where useful studies become possible with small rodents such as mice or rats (Fig. RD18–1). As a result PET is now becoming an essential tool in the development of new drugs and in the imaging of gene expressions. In response to the demand from the biomedical research groups, Crystal Clear has started the development of improved small- animal PET scanners, and of dedicated PET scanners for breast cancer examinations.

108 Experimental Physics Division Fig. RD18–1: The First ClearPET small-animal PET scanner was recently ﬁnalized, and this instrument is now available commercially.

The Collaboration is organized around a number of local centres. Each local centre establishes contacts with the biomedical community and obtains funding to participate in the Crystal Clear project. At present ﬁve centres have been set up and funded: Belgium (Vrije Universiteit Brussel and Universiteit Gent), France (Université Claude Bernard Lyon), Germany (Forschungszentrum Juelich), Switzerland (EPFL Lausanne), and Portugal (LIP, Lisbon).

These groups will build, in close collaboration, four more or less identical small-animal PET scanners for their associated biomedical research groups. In addition a dedicated PET system for mammography (PEM) is being developed in collaboration with several medical teams in Portugal, France, and Belgium.

We shall improve the PET technology by introducing the following innovations:

– New scintillating materials: LuAP is a new scintillator developed by Crystal Clear, and it is a good alternative for LSO. It is most useful in combination with LSO in a ‘phoswich’ to determine the depth of interaction. In collaboration with JSV Bogoroditsk Techno-chemical plant in Russia, the Institute for Physical Research, Astarak, Armenia and the company Photonics Materials we are optimizing the characteristics of this material and developing the technology for its industrial production (Fig. RD18–2).

– New photodetectors: Avalanche photodiodes are an alternative to the traditional photomultiplier tubes since they are more compact, are more easily subdivided in small pixels, and are potentially lower cost.

– New readout electronics: The analog detector signal is immediately digitized, and all subsequent processing is done by software. This allows more accurate time and energy information to be extracted from the signals.

– Systematic use of simulation programs: The design of the PET scanner is based on GEANT4 simulations. This allows the design of the system to be carefully optimized. This is standard practice in high-energy physics, but all commercial systems are designed in a more traditional way.

Experimental Physics Division 109 Close collaboration with biomedical research workers and with commercial companies is a key element in the strategy of Crystal Clear. Each local centre establishes close relations with the local biomedical research groups, and these groups are usually associated with the applications for funding. Crystal Clear has also concluded collaboration agreements with several commercial companies.

Fig. RD18–2: 9000 LuYAP crystals for use in PET scanners were produced by the Bogoroditsk Techno-chemical plant in collaboration with Crystal Clear.

RD39 – Cryogenic Tracking Detectors

The CERN RD39 Collaboration made significant progress in 2003 in the development of ultra radiation- hard cryogenic silicon (Si) detectors for applications in experiments at the LHC, in particular for its future luminosity upgrade. The detailed modelling of the Lazarus effect showed that the electric field in irradiated Si detectors can be easily manipulated by the filling state of two deep defect levels at cryogenic temperatures. Based on this finding, advanced radiation-hard detectors using charge or current injection were developed by RD39. In such detectors, called Current Injected Diodes (CID), the electric field is controlled by the injected current, which is limited by the space charge. A nearly uniform electric field in the detector can be obtained, independent of the radiation fluence. Different modes of current or charge injection were studied:

1. the charge injection mode using a LED or laser as a light source;

2. the ohmic current injection mode using the symmetric p/n/p structure (after radiation beyond space- charge sign inversion it becomes p/′′p′′/p); and

3. the forward current injection mode using the p/n/n junction diode structure operated at forward bias potential. It was found that CID detectors can be operated in the temperature range of 100 K to 200 K with much improved charge collection efﬁciency as compared with room temperature operation.

The analysis of the data from high-energy beam tests of the edgeless Si detectors at cryogenic temperatures has shown very good results with a sensitivity up to the physical edge of the detector. The thickness of the dead layer at the edge was determined to be compatible with zero, within the experimental error of ±12 µm.

New techniques to study radiation-induced defects and carrier lifetime degradation, such as the defect spectroscopy using the Lazarus effect and the contactless microwave lifetime set-up, were developed. Future studies are now under way for developing ultra-hard cryogenic Si detectors for the LHC luminosity upgrade, 16 2 using samples already irradiated up to a ﬂuence of 10 neq/cm , at which trapping will limit the charge collection depth to a range of 20 µm to 50 µm regardless of the depletion depth. Preliminary investigations

110 Experimental Physics Division indicate that temperatures lower than 80 K may be needed for minimizing the charge loss due to trapping, and new measurement equipment is being designed.

Precision tooling was designed and fabricated for the assembly of large microstrip detector modules, and equipment was prepared for the tests of ceramic hybrids of the CMS experiment, as well as for the RD39 modules, down to 80 K temperature. Figure RD39–1 shows the ﬁrst assembled module, which has undergone successful thermal and mechanical tests.

Fig. RD39-1: Large (5 × 6 cm2) microstrip detector module of RD39, featuring a miniature cooling pipe integrated between the pitch adapter and the Si support plate, on which the sensor, pitch adapter, and ceramic hybrid are precision assembled. (Hybrid: courtesy of the CMS Collaboration.)

RD42 – Development of Diamond Tracking Detectors for High-Luminosity Experiments at the LHC

Single-Crystal CVD Diamond Samples

During the year 2003 emphasis was put on further development (together with the Element6 Company, former DeBeers) and understanding of the characteristics of single-crystal CVD diamond. The very narrow Landau distribution in Fig. RD42–1 shows the most probable charge of 13500 e–h pairs corresponding to a charge collection efﬁciency of above 90% in this 450 µm thick sample. The insert in Fig. RD42–1 shows for comparison the Landau distribution measured on one of the best polycrystalline samples.

Fig. RD42–1: Landau distribution measured with single-crystal CVD diamond from Element6. The insert shows the Landau distribution from a high-quality polycrystalline CVD RD42 diamond sample for comparison.

Experimental Physics Division 111 High-Quality Polycrystalline Diamond Sample for a Full-Sized ATLAS Pixel Module

Preparations have continued to construct a full-sized ATLAS diamond pixel module (2 cm × 8 cm) to be equipped with the latest version of the fully radiation-hard ATLAS front-end chip FE-I3. The bump bonding of the chips to the detector will be done by inserting the polycrystalline CVD diamond detector into a silicon carrier wafer at the IZM company.

To obtain a high quality diamond detector of that size, a full 4.5 inch diamond wafer produced by Element6 has been metallized with a total of 97 dot contacts, which are uniformly distributed over the whole wafer on both sides of the wafer (Fig. RD42–2).

Very high charge collection distance (ccd) is measured over the whole wafer (average thickness of ~1 mm) with the central dot giving the best value of ccd = 292 µm at an electric ﬁeld value of E = 0.9 V/µm. This is the highest ccd value observed so far by RD42 on polycrystalline diamond. It should be noted that this wafer has not been processed on either side (lapped, polished) as can be seen in the photograph. The surface is very rough and one can distinguish with the naked eye the single monocrystals in the material (bright points). The 2 cm × 8 cm piece for the ATLAS pixel module will be cut from the central part of the wafer.

Fig. RD42–2: Unprocessed poly-crystalline CVD diamond wafer (growth side) foreseen for full-scale ATLAS pixel module.

CVD Diamonds for Beam Monitoring and Abort Systems

CVD diamond detectors have been installed as beam monitors in both B-factory experiments, the BaBar, experiment and the BELLE experiment (Fig. RD42–3) and are fully operational.

The CMS and ATLAS experiments have set up groups to study applications of diamond detectors as beam loss and condition monitor close to the beam pipe. Tests have been performed with a polycrystalline CVD diamond detector with 9 pads with a pad size of 2.5 mm × 2.5 mm for application as a high-speed single- particle beam monitor for hadron therapy in proton and heavy-ion (carbon) accelerators. Successful tests have

112 Experimental Physics Division been performed at the high-intensity proton accelerator at IUCF in Indiana using a 330 MeV/c momentum proton beam. A 2 GHz bandwidth current ampliﬁer was connected to the diamond pads and analog pulses from single particles could be recorded (Fig. RD42–4). The rise time of the pulses is 340 ps with a pulse width of 1.3 ns FWHM, showing that accurate single-beam monitoring in such facilities is feasible.

Fig. RD42–3: BELLE CVD diamond beam monitor installed close to beam pipe (black arrow).

Fig. RD42–4: Analog pulses from single 300 MeV/c protons recorded with a 2 GHz band width current ampliﬁer. The main ﬁgure shows the pulse form averaged over many single pulses, the insert shows a measurement of a single pulse.

RD50 – Radiation-Hard Semiconductor Devices for Very High Luminosity Colliders

The objective of the CERN RD50 Collaboration is the development of radiation-hard semiconductor detectors for very high luminosity colliders, particularly to face the requirements of a possible upgrade scenario of the LHC to a luminosity of 1035 cm–2 s–1, corresponding to expected total ﬂuences of fast hadrons above 1016 cm–2 and a reduced bunch-crossing interval of ~10 ns. The CERN RD50 Collaboration was approved by the CERN Research Board in June 2002.

Experimental Physics Division 113 The collaboration currently consists of 270 members from 51 institutes (Barcelona, Bari, Berlin, BNL, Bologna, Bucharest NIMP & University, CERN, Dortmund, Erfurt, Exeter, Fermilab, Florence, Glasgow, Hamburg, Helsinki, Ioffe Institute, ITME, Karlsruhe, KINR, Lancaster, Lappeenranta, Liverpool, Ljubljana, Louvain, Milano, Minsk, Modena, Montreal, Moscow ITEP, Moscow Kurchatov, New Mexico, Oslo Sintef, Oslo University, Padova, Perugia, Pisa, Prague Academy, Prague CTU & Charles University, PSI, Purdue, Rutgers, Santa Cruz, Shefﬁeld, Surrey, Syracuse, Tel Aviv, Torino, Trento, Trieste, Valencia, Vilnius). More details can be found at the collaboration web-site: http://www.cern.ch/rd50/. During this year three workshops and collaboration board meetings were held at CERN to discuss the recent results and coordinate the research activities of RD50: 2–4 October 2002, 18–20 May and 3–5 November 2003. Each workshop registered a high rate of participation, with an average of 80 participants and about 34 talks. The research activity of RD50 was presented in the form of invited oral contributions at several international conferences.

There are two lines of research activity in RD50, each composed of three projects, having several common activities and working groups, as shown in Table RD50–1. The main results of each project are brieﬂy presented in the following.

Defect and Material Characterization

For the ﬁrst time it has been shown that both the change of the effective doping concentration (depletion voltage) and the free charge carrier generation (reverse current) can be completely understood by the formation of defects detected by spectroscopic techniques. The ‘I’ defect, of amphoteric nature having both an acceptor state at Ec – 0.54 eV and a donor state at Ev + 0.23 eV, proved to be the main cause for the observed inversion of the space charge sign in the depletion region of standard FZ Si diodes irradiated with gammas up to 300 MRad. The fact that this defect is not present in Diffusion Oxygenated FZ Si (DOFZ) after the same kind of irradiation makes this latter material more radiation resistant. Moreover, microscopic studies made on Czochralski Si after irradiation showed evidence that the formation of shallow oxygen related donors by irradiation play a major role in the macroscopic behaviour of the Cz-devices. These results are seen as a major breakthrough in the understanding of radiation damage and it is hoped that they will pave the way for an optimization of radiation-tolerant detectors including hadron-induced damage.

Defect Engineering

This project has provided the DOFZ and high-resistivity Cz Si for the development of radiation-resistant detectors. Moreover, for a different approach to increasing the radiation tolerance of silicon, this project has further developed thin detectors made with low-resistivity epitaxial silicon layers. A first production of detectors on 50 µm thick low-resistivity (50 Ωcm) epitaxial silicon layers grown on Cz substrates by ITME, Poland was completed. The superior radiation tolerance of these devices with respect to the radiation-induced change of the depletion voltage has been demonstrated for irradiations with 20 GeV protons, 58 MeV Li ions and reactor neutrons up to fluences of 1016 cm–2. For the charged hadron damage no type inversion is observed, which can be explained by a generation of shallow donors which overcompensates the creation of deep acceptor like defects at high fluences.

114 Experimental Physics Division The working group devoted to the study of oxygen dimers in silicon has carried out a ﬁrst dimerization process of silicon by irradiation of 3 mm thick Cz samples of different oxygen and carbon concentration, a 3 mm thick FZ sample, and different 300 µm thick diodes (FZ, DOFZ and Cz) with 6 MeV electrons at 350°C up to a ﬂuence of about 1018 cm–2. First electrical characterizations and TSC measurements on the different diodes have shown that the devices are heavily damaged and cannot be operated at full depletion. Further studies are in progress.

Table RD50–1: Scientiﬁc organization of the CERN RD50 Collaboration

Spokesperson / Deputy Mara Bruzzi (INFN and Univ. Florence) / Michael Moll (CERN)

Working Groups and Line Project Convener Main Research Activity Common Acitivities

Defect/Material Characterization of the microscopic (1) DLTS calibration Characterization properties of standard, defect (B.G. Svensson) Bengt G. Svensson engineered and new materials, pre- Univ. Oslo, Norway and post-irradiation

Defect Engineering Development and testing of defect (1) Oxygen dimer Eckhart Fretwurst engineered silicon: oxygen (M. Moll) Material Univ. Hamburg, enriched FZ (DOFZ), high res. Cz, Engineering Germany epitaxial, Si enriched with oxygen dimers

New Materials Development of new materials with (1) SiC (I. Pintilie) Juozas Vaitkus promising radiation-hard (2) GaN (J. Vaitkus) Univ. Vilnius, properties: bulk and epitaxial SiC, (3) Other materials Lithuania GaN

Pad Detector Characterization of macroscopic (1) Standardization of Characterization properties of heavily irradiated macroscopic Jaakko Harkonen single-pad detectors in different measurements Helsinki Inst. operational conditions (A. Chilingarov) Physics, Finland (2) Common irradiation

New Structures Development of 3D, semi-3D and (1) 3D (M. Rahman) Device Mahfuzur Rahman thin detectors and study of their (2) semi-3D (Z. Li) Engineering Univ. Glasgow, UK pre- and post-irradiation (3) Thinned detectors performance (M. Boscardin)

Full Detector – Systematic characterization of (1) Comparison between Systems segmented (microstrips, pixels) detectors made by Gianluigi Casse LHC-like detectors different Univ. Liverpool, UK – Links with LHC experiments manufacturers

Experimental Physics Division 115 Pad Detector Characterization

A wide campaign of irradiations has been performed on single-pad detector structures made with standard FZ, DOFZ and CZ Si with different particles, energies and fluences of up to 1016 cm–2. Measurements of macroscopic parameters (leakage current, full depletion voltage, charge collection efficiency and annealing parameters) have been carried out in collaboration with the Defect Engineering project. High-resistivity Czochralski grown Si detectors (crystal growth by standard and magnetic field assisted Czochralski methods) have been found to be less sensitive to radiation-induced changes of the full depletion voltage than standard Fz-Si or diffusion oxygenated Fz-Si (DOFZ). The leakage current in gamma and low-energy proton irradiated oxygenated Si (Cz-Si and DOFZ) detectors seems to be smaller than in standard devices. This is believed to be due to the non-clustered point defects induced by this kind of radiation. Design and processing of common RD50 test structures has started and the production of common devices is in progress.

New Materials

Semi-Insulating (SI) vanadium-compensated SiC detectors (thinned to 100 µm) have been studied before and after irradiation with 1013 pions/cm2: the measured charge collection efﬁciency (CCE) was 60% prior to irradiation and 50% after. The results suggest that vanadium is destructive for the production of SiC detectors. New SI-SiC samples without vanadium will be provided by Okmetic, Finland next year.

Epitaxial SiC detectors have been characterized, before and after irradiation: a 100% CCE has been observed with α and β-particles (90Sr) in unirradiated detectors with a thickness of 40 µm. The signal is stable and reproducible: no priming or polarization effects are observed. No increase in the leakage current was observed after irradiation up to the highest fluence/dose in epitaxial 4H-SiC detectors irradiated with electrons (8.2 MeV) and γ-rays (60Co source) at fluences and doses up to 9.48 × 1014 e/cm2 and 40 Mrad, respectively. After irradiation with 8 MeV protons up to a fluence of 1014 cm–2 the CCE (measured with α-particles) was about 80%. These results are encouraging for the development of epitaxial SiC detectors. Six high-quality, 2-inch, n-type, 4H-SiC epilayers (maximum thickness 50 µm and different doping) were grown by IKZ- Berlin. A mask for processing Schottky contacts was designed and fabricated: the first batch of common test structures has been produced and will be studied next year.

New Structures

One primary task for this year has been to design 3D detector structures and readout electronics suitable for LHCb/VELO trials. The design and masks for the VELO have been completed and the electronic readout of the 3D device was successfully operated using a different chip. 3D devices were manufactured and irradiated with pions up to 1014 cm–2. There was a slight degradation in the charge collection efﬁciency from 60% down to 45%, but the results are promising. Semi-3D structures have been intensively simulated, the design has been implemented and the processing of the ﬁrst batch of test structures is nearly complete. Thin single-pad detectors have been designed and manufactured with thickness down to 57 µm. Electrical characterization of non-irradiated thin devices has been performed, showing good performance.

116 Experimental Physics Division Full Detector Systems (FDS)

First miniature microstrip detectors with oxygen-enriched FZ, CZ, epitaxial and p-type substrate silicon have been manufactured. Pixel and microstrip miniature and full-sized detectors produced with standard and oxygen-enriched substrates were used for systematic studies of the charge trapping parameters. Some of these detectors have been irradiated up to 1016 24 GeV/c p/cm2: tests are in progress. The design of an RD50-FDS mask set for microstrip detectors has been carried out using input from experiments and simulations. Manufacturing is under process. Simulations have been carried out to determine the survival scenario of pixel devices with different thickness and geometries in the ﬂuence range up to 1016 cm–2. A number of research activities have started in collaboration with experiments at the LHC, as listed here: a test beam with 120 GeV muons and pions on a Cz Si microstrip detector has been carried out in collaboration with LHCb VELO; the manufacturing of pixels with Cz Si in collaboration with the CMS pixel group has been decided; the simulation of the efﬁciency of pixels with ATLAS geometry has been carried out up to 1016 cm–2; devices with different distances of the active volume from the cut edge have been designed.

Technical Developments

Technical Assistance Group TA1

In 2003 the group continued its support for the main LHC commitments, the TRT of ATLAS, the Tracker and the E-Cal of CMS. In many respects this activity is now moving toward assembly and integration of the detectors.

Full technical support to NA60 was also supplied, some work and consultancy for CAST and TERA were also provided. Some help was given to HARP.

The basic services for the scintillator workshop and the wiring of frames for wire chambers were also maintained.

The sections Gas Systems and Semiconductor Detectors (bonding lab, thin ﬁlms and irradiation facility) did a considerable amount of work to meet the demands of all LHC and ﬁxed-target experiments.

After the successful commissioning of the Tracker for COMPASS, based on GEMs, the Gaseous Detectors Section continued with the study of performance and applications of GEMs-based detectors.

ATLAS Transition Radiation Tracker (TRT)

In 2003 the design of the 8-plane module, i.e. the assembly of two basic 4-planes, was completed, while the first 8-plane modules produced by the two Russian sites arrived at CERN. Substantial technical and logistic support, as far as procurement, tools and procedures is concerned, was supplied together with operations of repair and modifications of the wheels produced. In the second half of the year the work of the TA1 team focused more on the preparation for end-cap assembly and integration in the surface building. In this respect the two devices to stack the wheels in their final modularity were designed, and the components ordered and mounted.

Experimental Physics Division 117 At the same time, the rig to assemble, hold and align the barrel support structure was built, the various elements of the structure (outer and inner cylinders, end frames) arrived at CERN and were checked. Very soon this structure will be handed over to the American team to start the installation of their modules.

CMS Silicon Tracker Outer Barrel (TOB)

During 2003 the TA1 group continued its responsibilities for the design, procurement, and assembly of the CMS Silicon Tracker Outer Barrel (TOB), and participated in the design and prototyping of the services and integration of the CMS Tracker. An X-Y table for scanning TOB silicon detector rods with a radioactive source was produced and commissioned. This setup will be used by the CMS Tracker group for the quality control of all the completed rods. Final tests of a full TOB cooling segment were successfully completed. Production and testing of the final cooling pipes for the rods started in 2003, and they are due to be ready in 2004. Sets of tooling for rod assembly and handling were designed, produced, and distributed to the detector assembly sites at CERN, Fermilab, and Santa Barbara. A full-scale mock-up of the TOB support wheel was designed and constructed, and its compatibility with the CMS Tracker Support Tube scale-1 mock-up was tested. Further integration tests are planned for early 2004. The tendering for the TOB support wheel components in carbon fibre was done, and the contract placed in September 2003. The wheel component deliveries are expected by April 2004, allowing the final full assembly of the TOB detector during 2004 and 2005.

CMS End-Cap Ecal

From the beginning of 2003 TA1 participated in the CMS crystal calorimeter end-cap project. TA1 has the responsibility for the assembly of the E-Cal End-Cap (EE) super-crystals (5 × 5 crystals) onto the mechanical structure of the end cap. In addition, TA1 will set up a regional centre for the assembly of part of the 624 super-crystal structures. During 2003, the various tasks were assessed and contacts were made to agree on procedures and solutions. Drawings were prepared of the EE assembly frames. The attachment scheme of the EE structure onto the hadron calorimeter was finalized and built. The layout of a new EE assembly laboratory in Hall 168 was defined and its construction started in December 2003. A dummy structure for the final EE and pre-shower cabling in CMS was designed and tested in a cabling mock-up. In parallel, the TA1 group participated in building the software control and sensor readout of a new cooling plant for the CMS E-Cal test beam. This cooling plant provides cooling water with 0.01˚C temperature stability and serves as a prototype for the E-Cal cooling plant in CMS.

HARP

During 2003, TA1 continued its technical responsibility for the HARP experiment. In the beginning of the year, assistance was given to an electronic check-out of all 4000 TPC electronics channels. In parallel the HARP dismantling was pursued in order to free the experimental area space for ATLAS and LHCb. During the spring, the HARP solenoid and TPC were removed from the T9E area to the T9 area. The TPC cabling and gas facility were adapted to the new position. This allowed the performance of further TPC calibrations and systematic checks with radioactive sources.

118 Experimental Physics Division TA1 Gas Systems (GS)

The year 2003 has been one of intensive construction for the final LHC gas systems. The CMS distribution modules are mostly completed and approximately 30% of the racks have already been delivered to P5 for installation. The ALICE TPC gas system was fully completed during 2003, which makes it the first LHC gas system where both the pipe work and the controls are finished. The TPC gas system will now be used to test and debug the first version of the control software.

Besides the work on the ﬁnal systems, the TA1 gas section has carried out intensive studies on contaminants that could cause ageing inside the ionization detector. The most dangerous contaminants are trace pollutants from Si containing lubricants that might be present in gas system components. Together with the chemical department of EST and the ATLAS TRT group we have started a campaign to check individual gas system components on their cleanliness. The goal is to establish a positive list of gas system components that are proven to be harmless for the chamber operation under LHC conditions. The positive approval of a component is done through either an ageing test or by a chemical analysis.

The section continues the gas support work for the LHC test activities and the ﬁxed-target experiments. In 2003 these were in particular the support for the various ageing tests in GIF.

TA1 Semiconductor Detectors (SD)

Support Activities

The major activities in the Thin Film Lab (Bldg. 3) concerned the preparation of production of CsI photocathodes for ALICE HMPID and mirror coatings for LHCb RICH-2. The VUV scanner was successfully commissioned and produced excellent results on full-scale CsI prototype cathodes. The large surface evaporation plant (originally built in the 1980s for DELPHI) was dismantled, completely overhauled, and is now being reassembled in a new lab in Bldg. 108. The control hardware and software is being upgraded. A high-reflectivity light guide based on a multi-layer reflective film on a Mylar substrate was developed for the CMS HF system. The production of 100 m2 of this film was contracted to industry. Support in thin film and glass/ceramic technology was provided to numerous clients, such as ALICE, CMS, COMPASS, and LHCb.

The ﬁrst batches of the series production of the CMS tracker hybrids were bonded in the divisional Silicon Facility (DSF, Bldg. 186). The output is approaching the nominal value of 30 hybrids per day. In 2003 there was still a high pre-series and prototype fraction, e.g. NA60 pixels, TOTEM, ALICE pixels and microelectronics. After the procurement of a third bonding machine of the type Delvotec 6400 (second-hand) the lab is now well prepared for LHC production bonding. ALICE and LHCb have started the preparation of the DSF large clean room area for assembly and testing of their Inner Tracker System and Pixel HPD components.

The irradiation programme in the neutron and 24 GeV/c proton irradiation facilities (PS East-Hall 150) remained very busy. Close to 600 samples (detectors, electronics, materials) were irradiated and almost the same number of dosimetric analyses has been done for 65 users from 30 institutes. This comprised also unusual objects like PbWO4 crystals from CMS and active components with online readout during irradiation. A considerable amount of maintenance effort and upgrade work assured a high availability and user- friendliness of the facility. Radiation monitoring in the LHC detectors will require reliable and cheap sensors.

Experimental Physics Division 119 RADFETS, p-i-n diodes and optically stimulated luminescence detectors have been characterized for this purpose.

Detector Development

Experimental studies, performed in the framework of the RD50 Collaboration, were focused on characterization and optimization of novel defect engineered silicon material, so-called oxygen-dimerized silicon. A solid-state detector lab has been set up in Bldg. 28; this disposes of the necessary equipment to carry out characterization measurements like capacitance (C-V), reverse current (I-V) and charge collection (TCT) measurements. As a service the equipment was made available to various users like NA60, CMS, TIS-RP and EP-MIC.

The development of Hybrid Photon Detectors (HPDs) led to the production of the ﬁrst fully operational 10-inch HPD, the largest HPD ever built. A prototype of a proximity-focused HPD, especially designed for medical imaging applications like PET, was built and characterized. The tube body is produced by active brazing from ceramic rings and niobium electrodes. The section participated in the submission of two funding applications in the EU Framework, Programme 6, with the purpose of transferring and applying technologies developed for particle detectors in medical imaging.

TA1 Gaseous Detectors Development (GDD)

The section continued the technical support to COMPASS, helping with maintenance of the GEM detectors on the floor and the completion of two reserve chambers. In collaboration with the Trieste team, the reasons for discharge problems met with by the COMPASS RICH chamber were investigated, with the installation and operation of one detector in the laboratory. Major findings are the possibility of introduction of metallic shavings during the assembly, and the formation of organic polymers in discharges. A possible process of CsI quantum efficiency ‘pumping up’ with the photons emitted in discharges has been investigated in collaboration with TA1-SD. It could explain the very long memory observed in the RICH chambers after a discharge.

A line of investigation on a fast RICH device using GEMs as multipliers has started; efﬁciency and position accuracy of a CsI triple-GEM detector has been measured. With the help of the electronics group in ALICE, a new data recording and acquisition system using the ALTRO chip has been procured, with a view to detailed studied of resolution of a GEM detector wth Hexaboard readout, both for RICH and TPC applications. The last is a cooperative work with the MICE experiment that has adopted the new technology.

The large diffusion of GEM studies and the adoption of the technology for many experiments and applications required a continuous effort of consultancy and support.

Technical Assistance Group TA2

During 2003 the group collaborated with and provided technical assistance to several experiments. The collaboration with LHC experiments continued. As in previous years the group provided support for some ﬁxed-target experiments.

120 Experimental Physics Division COMPASS-NA58

The group collaborated with COMPASS-NA58 in the ﬁelds of technical co-ordination, integration, and the installation of the experiment. After the 2002 run, nine new double layers of the large-area straw detector from JINR were installed on new support structures. Two more large-area drift chambers were refurbished by Russian colleagues under the coordination of TA2. The characteristics of these chambers in beam was analysed and optimized. The production of the ECAL inner cassette continued during 2003 and the structure was delivered in November. The assembly has started and it should be integrated into the spectrometer before the 2004 run. The new target solenoid has been wound by an outside company and the assembly has started. It was, however, decided not to push for installation for the 2004 run but rather to improve the instrumentation and go through a thorough testing at DAPNIA, Saclay. TA2 continued to provide special support for the RICH detector. A careful leak testing reduced the radiator gas losses to a minimum and guaranteed full UV transparencies during the 2003 run. The cleaning of further C4F10 gas ensured the complete ﬁlling of the 80 m3 RICH vessel. A new, more automatic cleaning plant was designed and installed by TA2. Two poorly performing photon detectors were refurbished at Trieste. A third chamber was replaced by a spare chamber. Thus all photon detectors operated satisfactorily during the 2003 run. Support was also given for the mounting of the photon detectors and the geometrical re-measurements of the RICH mirrors.

The amount of data taken in 2003 is comparable to that of 2002. The experiment suffered from the accelerator problems where the beam availability dropped from 80% in 2002 to 54% in 2003.

CAST

Since the start of 2003, the group has been collaborating with the CAST experiment in the ﬁeld of technical coordination. The main areas have been the supervision of modiﬁcations to the mechanical movement system of the telescope, improvements to the vacuum and interlock system to allow safe operation of the X-ray telescope, integration of new detectors, and additions of shielding to reduce detector background levels.

The group is collaborating with three of the LHC experiments:

ALICE

The group continued the collaboration in the construction of the field cage for the ALICE TPC. All mechanical components of the field cage have been received from European industry and assembled in the SXL hall at point 2. Tests concerning the leak tightness as well as the HV behaviour were successfully performed. All parts needed for the equipment of the field cage were manufactured and tested. The equipment of the field cage with the high-voltage membrane and the potential strips is well advanced.

The group also supports the HMPID detector. Two of the seven detector modules have now been wired, assembled and successfully tested with high voltage. The wiring of the third module has now been completed.

Experimental Physics Division 121 A total of 42 photocathodes (PCs) will be needed to instrument these modules. A PC comprises two multilayer pad PCBs precision glued to an aluminium frame. The production of a 100 PCBs has now been launched after some delays; the production is made completely in-house (TS-DEM and TS-MME) apart from the surface mounting (SMD) of the connectors. In order to handle larger SMD batches, tooling has been prepared and tested in collaboration with an outside ﬁrm. At present there are 48 PCBs in various stages of the production chain. Two production PCs have been successfully made and tested and four more are being assembled.

The HMPID modules in ALICE are supported by a large frame (‘cradle’). The cradle ﬁnal design has recently been completed – optimizing the rigidity of the structure and the compatibility with the gravity-ﬂow liquid radiator circulation system.

CMS

For the CMS Pre-shower Detector the group has finished the final design including the complicated integration drawings for all the services. The two support cones have been manufactured. The method of flux- less brazing for the aluminium cooling screens has been optimized, and preparations for the final production of the cooling screens are ongoing.

LHCb

The development of the pixel-HPDs was successfully pursued in 2003 in collaboration with the EP-ED, EP-MIC and EST-SM groups. An adaptation of the bump-bonding process was worked out together with industry in order for it to be compatible with the thermal treatments required by the HPD manufacturing process. A ﬁrst batch of bump-bonded LHCb pixel chip assemblies using a high-melting-point bump solder gave very encouraging results. This was followed by the realization of two HPD prototypes encapsulating two such assemblies. These prototypes were characterized in detail in the laboratory and during two beam-test campaigns using air and aerogel as Cherenkov radiators. These HPDs operated very satisfactorily. In parallel to this activity, HPD ageing tests were carried out and resulted in no observable degradation of the tube performance. At the end of 2003, a LHCb-RICH photon detector review was carried out, and the LHCb-RICH group decided to conﬁrm the choice of the HPDs as RICH photon detector.

Two RICH2 PRRs were achieved in 2003: all the mechanic and opto-mechanic structures were finalized and have entered the production phase. The spherical mirrors for RICH 2 have started to be delivered; their coating has been defined and will be performed at CERN in 2004 under the responsibility of TA1. A prototype of the mirror wall has been mounted and commissioned in Hall 156. For RICH1, alternative technologies for the mirrors, including thin glass mirrors, beryllium, carbon fibre, electroformed and composite based mirrors, to save on the material budget, are still being actively pursued. In particular, beryllium-glass coated mirrors have reached a quality and reliability level such as to become the preferred option for the mirror system in RICH1. The group collaborated with the Rutherford Appleton Laboratory to manufacture in situ (Bldg. 156) the two RICH2 composite-based entrance and exit windows.

122 Experimental Physics Division Generic Research and Development

The group continues to support R&D work on the ISPA tube and the Pixel HPD for non-high-energy- physics applications. We are collaborating on a speciﬁc pixel chip design for low-energy electron detection; a ﬁrst prototype has been produced and tested. For the readout electronics, an analog mezzanine card and its master control card, featuring a FPGA and a DSP, were developed and produced in 2003 and are being tested.

Technical Assistance Group TA3

In order to improve our support to external users, our mechanical workshop has been reorganized. Continuous supervision and support to users has been set up.

The assembly areas in Bldgs. 168 and 164 have been reorganized; storage areas have been removed to provide working space for the group and for users.

The main activities of the group are oriented towards the LHC experiments; however, we give some general support to ﬁxed-target experiments in the MP and TS sections.

Section TA3-MP

The section is in charge of the repair, modiﬁcation, maintenance and installation of most of the experimental magnets. In 2003 the section had to do some repair work on the NA48, NA60 and COMPASS magnet.

The section provides assistance to users concerning magnetic field measurements or infrastructure to study effects of magnetic field on various pieces of equipment. In 2003, for example, the section provided the necessary calibrated Hall probes and readout to measure precisely the magnetic field in the decay channel and helium tank of NA48. It provided assistance to ATLAS to measure the influence of the expected magnetic field on various pieces of equipment like vacuum gauges or electromagnetic compressed-air valves.

The section developed the hardware in collaboration with NIKHEF and software for a 3D Hall probes calibrator. This will be used to calibrate the Hall probes to be used for the magnetic ﬁeld measurements of the LHCb and ALICE experiment, and to calibrate the Hall probes for the ATLAS Toroid Magnet.

The section performs calculation on magnetic ﬁeld using the TOSCA program, as done, for example, for the LHCb magnet and shield, and for the ALICE magnet.

Support is also maintained for running projects like CAST or COMPASS.

Section TA3-IC

The main activity of the section is the common project for LHC experiment on the experimental magnets control system (MCS) and magnets safety systems (MSS).

Experimental Physics Division 123 – ALICE: The study for the dipole instrumentation, and installation of the MCS and MSS has been completed. The upgrading of the L3 multiplexer allowed the readout of the 1200 temperature sensors. The whole system was successfully tested in autumn 2003, during the power test.

– ATLAS: After the recabling of the valve unit, to replace non-conforming cables, the chimney for the central solenoid was retested. The construction and assembly of the control and safety systems for the solenoid started in autumn 2003. It should be completed and ready for the test in spring 2004. The processes for the vacuum system control have been programmed under the UNICOS speciﬁcations and tested in the assembly area of Bldg. 180. With some support from the MP section the study for the external cabling was completed. Cables and junction boxes will be ordered at the beginning of 2004.

– CMS: The test area has been set up. The power converter and the DCCT have been delivered and will be tested at the beginning of 2004. The main contactors have been received and are being installed. The inquiry concerning the vacuum system has been done, and the reception tests in the factory using the control system designed under the UNICOS speciﬁcations are expected at the beginning of 2004.

– LHCb: The study for the instrumentation has been completed. All the components have been realized and tested. The cabling will start at the beginning of 2004. The equipments and components concerning the MCS and MSS have been delivered and tested. The assembly of the MCS and MSS will start in January 2004.

Section TA3-TS

As previously mentioned, the section provides technical assistance to users through access to our workshop, assembly space, or direct mechanical assistance.

The main user of the workshop is ATLAS. Mechanics from various institutes use our machines and get some assistance. This support concerns the tile calorimeter, the liquid argon cryostats, or the installation at point 1.

The supervisor of the workshop executes some small mechanical jobs, as for example for NA60, for ATLAS.

– ATLAS: The group is involved in various aspect of the project.

a) Tile calorimeter detector: assembly, mechanics, logistics, and help to outside users.

b) Barrel liquid argon EM detector: assembly, mechanics, logistics, and help to outside users.

c) Barrel toroid integration and installation.

d) Liquid argon cryostat integration: infrastructure, mechanics, assembly, and tests.

e) In mid 2003 the section also assisted the ATLAS muon group to prepare the infrastructure for the reception and tests of the muon chambers.

f) Management of the liquid argon cryostat and cryogenics projects; in addition it coordinates the activities of CERN groups and outside Institutes

124 Experimental Physics Division – LHCb:

a) Muon chambers: the section is involved in the design, prototyping, and construction of part of the muon chambers. The tooling was designed, constructed, and tested in 2003. Prototypes were successfully manufactured. The system is now ready for production. The tooling has been duplicated in collaboration with external Institutes for their own chamber production.

b) ECAL and HCAL: the section provided assistance concerning the material speciﬁcation, manufacturing process, production follow-up and quality control for both calorimeters.

– CMS:

a) The group continued its participation in various working groups on engineering and integration, experimental areas, cooling, services, and infrastructure.

– Fixed-target experiments:

a) NA48: technical assistance was provided for repair of the drift chamber at the beginning of 2003, for the re-alignment of the drift chambers and beam pipe, and for the installation of Hall probes in the helium tank. The section is in charge of the liquid krypton cryogenics maintenance, operation, and control.

b) NA60: mechanical assistance concerning some improvement and modiﬁcation of the pixel support.

c) CNGS: the group provides technical support for the horn construction, in collaboration with LAL. Test set-ups have been built and used to test the various elements provided by LAL. The group is also involved in coordination activities, especially for the installation.

Activities of the EP-ED Group

ALICE Pixels

The group contribution to the ALICE Pixel covers a range of activities such as ASIC implementation, modular electronics developments, optical links, test systems, test activities, and system integration. During 2003, EP-ED staff engineers, technicians and students provided wide technical and organizational support.

The successful design of the electronic system for this type of high-density detector is highly dependent on the achievement of an optimized miniaturization that involves different technological ﬁelds such as microelectronics, precision mechanics, cooling and power distribution. In this respect, three versions of the Multi Chip Module (MCM) assembly, one of the most complex elements of the on-detector readout electronics, were investigated: the Printed Circuit Board (PCB) version, the ceramic version, and the Sequential Build Up (SBU) version.

The PCB MCM was first built and successfully qualified with the prototype versions of both the ASICs and the optical link package. Tests conducted in the group laboratory facilities confirmed that this MCM was operative. The Pilot1 chip, entirely developed by the group, the Analog1 chip and the GOL chip, both designed in a shared collaboration with the MIC group, and the optical link package, developed in collaboration with STMicroelectronics Milan, were functionally validated. A stable and reliable functioning of the readout

Experimental Physics Division 125 system was proven. During the October ion test-beam period, several single-pixel chip assemblies and one full 10-pixel-chip half-stave were read out by this MCM, demonstrating for the ﬁrst time a successful operation of the overall readout system in its real environment.

The ceramic MCM was studied in order to improve the thermal dissipation behaviour of the assembly and a prototype was manufactured at the end of 2003. Tests are planned in the EP-ED laboratory during 2004 with the aim of comparing the new features.

In parallel with the ceramic MCM, the SBU MCM was also investigated. This more recent technology allows a faster and cheaper industrial production compared to the ceramic version, while preserving a similar thermal dissipation behaviour. The group has been working on the construction of one prototype, in order to decide on the ﬁnal solution during 2004, after the completion of the functional tests.

A new, improved test system, emulating the whole ALICE trigger and DAQ systems, was designed. It is based on a new VME card, Rudolf, and has a set of Labview programs for its operation. The construction of several units is planned. In addition to the hardware design, EP-ED put remarkable effort into the writing of the ﬂexible Labview software routines performing several types of tests, such as conﬁguration of the pixel system, automatic calibration and test of all single electronic devices in the readout chain, and running the full acquisition with online monitoring of the sampled data.

In 2003, the group achieved important results in the interconnection simpliﬁcation of the on-detector electronics. The pixels bus, realized in an aluminium/Kapton multilayer ﬂexible structure, was carefully tested together with one half-stave and its MCM. The reliable operation of both the analog and digital parts of the system using only two supply voltages and one single ground was proven.

The group played an important role in the overall study of the electronics integration. The location and dimensioning of the low-voltage power supplies were deﬁned, the cabling was ﬁnalized, and the location of the temperature sensors was chosen. Particular attention was given to the temperature probing study which required support of the group for simulations and measurement tests.

The last device of the DAQ chain under the responsibility of EP-ED is the Link Receiver mezzanine card. The ﬁnal version was designed and tested. Labview and C routines were developed and the card was successfully used in the October 2003 test beam to acquire data.

The major test units developed by the group until 2003 needed to be upgraded in order to follow the corresponding evolution of the readout system functionality. Part of the group resources was engaged to design a new set of test units for the debugging of the ﬁnal electronic system.

EP-ED is responsible for the design of the pilot digital chip and during 2003 a final modification was introduced on it to compensate for an error found on the pixel chips, which produced a wrong polarity of their Fastor output signal. The new pilot chip prototype was produced and tested, confirming that the pixel detector will be able to contribute to the construction of the low-multiplicity trigger function.

126 Experimental Physics Division LHCb Pixels

EP-ED continued its active involvement in the front-end electronics for the pixel hybrid photon detectors (HPDs) of the LHCb RICH. The beginning of the year saw the completion of the probe testing of a preproduction batch of eight LHCBPIX1 wafers using the system developed in EP-ED. This was followed by the delivery of wafers of silicon sensors, designed in the group in 2002. These two items together allowed the first trials of a new, high-temperature, bump-bonding process in industry. Following the positive evaluation of a new custom ceramic carrier specifically designed for these chips, some assemblies were packaged and retested on a modified test system. Two further batches of bump-bonded assemblies were delivered in October and showed an excellent bump yield and resistance to thermal cycling.

Assemblies from the ﬁrst batch were packaged and then encapsulated within phototubes, thus forming the ﬁrst full-scale HPDs with 40 MHz electronics and a thermally reliable bump-bonding process.

Two test-beams were carried out, the ﬁrst using the existing 40 MHz readout system for individual tubes, and the second using the system developed by EP-ED for the ALICE Pixel test-beam where three HPDs were operated together. The group provided electronics support for the setting up and running of these tests. The successful results led to the choice in October of the HPD as the photon-detector for the LHCb RICH detector.

Following this decision, EP-ED has been given the responsibility for the production of the readout chips and sensors, and quality assurance of the bump-bonded assemblies. The infrastructure is being constructed for mass production, both at CERN and in industry.

ALICE TPC

The group has the responsibility to coordinate the TPC electronic developments and test activities up to the input stage of the DAQ, here represented by the ALICE Detector Data Link (DDL), and it is engaged in the design of part of the front-end electronic system. The readout system consists of Front-End Cards (FECs) and Readout Control Units (RCUs), interconnected through a custom infrastructure, the Readout Backplane. Two ASICs characterize the core of the front-end system: the PASA and the ALTRO.

The PASA is based on a charge-sensitive amplifier and was designed by the University of Heidelberg in the 0.35 µm CMOS process by AMS. The manufacture of the full reticule mask set (engineering run) started in June 2003, and the first 500 samples were delivered at the end of August 2003. The characterization of the chip was performed in the EP-ED laboratory using the final version of the FEC. The tests showed that the PASA circuit meets all design specifications.

The ALTRO chip was designed by the group and was mass-produced in 2002. The mass-production tests started in September 2003 and are being done at the University of Lund; they will be completed in January 2004. The test system is based on a test board and on software routines developed by EP-ED. The chips are handled by a robot operating the full test sequence automatically. The mass-production tests conﬁrmed a production yield of 84%.

In 2002 the group produced the ﬁnal prototype of the 128-channel FEC, which includes the last version of all basic components. In 2003, all aspects related to the mechanical integration of the FEC in the TPC service

Experimental Physics Division 127 support wheel, the implementation of the on-board cooling system, the distribution of the power and grounding were systematically investigated.

An exhaustive test campaign, to verify the behaviour under radiation of each component of the FEC, was performed at the cyclotron machine of the University of Oslo by the EP-ED team. A 29 MeV proton beam was employed to verify both the Total Ionizing Dose (TID) effects and the Single Event Effect (SEE). A total of 195 devices were certiﬁed to satisfy the ALICE requirements.

During 2003, the group was engaged in preparing a market survey and a call for tenders related to the mass production of the FEC. The ﬁrst 50 FEC samples were produced by the adjudicated company with a satisfactory yield of 90%. The full production of 4800 units was started in December 2003 and will be completed by June 2004.

The communication between the RCU and the FECs is implemented via a fast-bus infrastructure, the ALICE TPC readout bus, based on a custom protocol. The possibility of implementing the readout bus as a ﬂexible printed circuit board was investigated. A prototype was developed by the group and its mechanical and electrical characteristics were successfully tested in the laboratory. This design was adopted as the baseline solution, abandoning the previous version based on a ribbon cable.

The design of the last module of the electronic front-end chain, the Readout Control Unit, was finalized during 2003 in a joint collaboration between EP-ED, the University of Bergen, and the University of Heidelberg. The design of the motherboard was completed by September 2003. Its two mezzanine boards, the DDL-SIU and the DCS/TRIGGER, are now available. The FPGA firmware, mainly developed by EP-ED, is well advanced and will be completed by February 2004. The final task of combining all individual components into one fully certified module, and their qualification for tolerance to single-event upset, will continue until April 2004.

A fraction of the ﬁnal electronics (1024 channels) was characterized in a test that incorporates a prototype of the ALICE TPC together with all the other available components of the ﬁnal system (detector data link, cooling system, and low-voltage power supply). The tests and the data taking were conducted at CERN with an important contribution from the group; EP-ED also coordinated the assembly of the whole electronics- system. The tests showed that the system meets all design requirements.

LHCb VELO

The contribution of EP-ED to the VELO project progressed in the direction of more evaluation tests for electronic front-end system components of the Vertex detector. This system consists of PR03 silicon sensors, Beetle 1.2 ASICs, 16-channel hybrids, and service electronic boards for the analog and digital signal transmission.

The final front-end ASIC Beetle 1.2 was developed during 2002 by the ASIC laboratory of the University of Heidelberg and was tested by the EP-ED team, both in the electronics laboratory and in test beams with the last prototype sensors. The laboratory measurements confirmed the overall good performance of the chip. Feedback provided by EP-ED allowed some modification of the design and the submission of a new Beetle 1.3 version in the summer of 2003.

128 Experimental Physics Division The existing test-beam readout system, based on VME units (CRAMS and RIO), was replaced with a much faster and more versatile ADC acquisition system already developed by the group for NA60 and the SCTA_VELO ASIC testing. A larger number of ADC channels, up to 100, can be read out, compared with 10 in the previous system. In addition, a more then ten times increase in the data collection rate and a better system stability drastically reduced the acquisition running time, allowing a more precise testing of a number of detector parameters within the allocated test-beam time. This new acquisition system was adopted by the collaborating institutes in Liverpool and NIKHEF, respectively for screening the sensor production and for the development of the VETO detector.

Other sensor technologies of potential interest to the LHCb VELO detector were read out by the new acquisition system: the GLAST silicon sensors and the Chochralski sensors. The group contributed to these tests.

LHCb Common Gigabit Ethernet Mezzanine Card

Hundreds of Level-1 modules in the LHCb experiment will generate data packets in programmable hardware and transmit these towards a common CPU farm. Two physical Gigabit links are needed per Gigabit interface since High Level Trigger (HLT) and Level-1 Trigger (L1T) streams have to be generated quasi simultaneously. EP-ED was committed to specify and build multi-channel Gigabit interfaces on standard mezzanine cards for a common use in the whole LHCb acquisition system.

The implementation of the SPI-3 bus of the networking industry allowed the design of a standard interface which requires a relatively simple FPGA logic on the Level-1 mother modules for the transmission of parallel data streams to multiple destinations. A theoretical total Rx/Tx bandwidth of 2 × 1 Gbit/s per link can be achieved.

The first reference design, a two-channel Gigabit mezzanine card with options for copper or fibre links was specified in March and produced in July 2003. The generation and transmission of LHCb-specific packets over IPv4 protocol constructed from an FPGA were demonstrated to be operational. The results were presented at the LECC Workshop in September 2003.

In view of the later demand of LHCb for more than two links per interface, in October 2003 the group launched the design of a quad Gigabit link mezzanine version, based on a new quad MAC chip from Intel. In collaboration with Tsinghua Univerity of Beijing, the ﬁrst version of the quad (optical only) card was produced in December 2003 and it is currently under test. A PCI driver and a dedicated suite of Labview test routines were developed to provide access to all MAC chip resources on the mezzanine.

LHCb AROC Programmable PCI Card

The Advanced ReadOut Controller (AROC) unit was designed by the group in 2003 as a buffered PCI card with user programmable FPGA logic for both test and readout applications. The AROC was speciﬁcally designed for testing multichannel Gigabit interfaces (double and quad versions), replacing the LHCb Level-1 motherboards which were not yet available, and for emulating applications of data generation and transfer from an FPGA on the LHCb Level-1 modules.

Experimental Physics Division 129 Two AROC prototypes were produced in August 2003 for the testing of the Gigabit Ethernet prototype cards and for the development of the ALICE PHOS Trigger electronics. Ten more AROC cards are now being produced by the Chinese collaborators who will integrate several of them into their local Gigabit link test and acceptance system.

ALICE PHOS Trigger Electronics

A new request for support came from the ALICE PHOS detector group to deﬁne the global architecture of their readout system and to help in prototyping the embedded Trigger Router Units (TRUs). The TRUs are custom cards, located, together with the PHOS Front End Electronics (FEE) cards, on the warm side of the PHOS modules. Both the FEE and TRU cards use the same key component, the ALTRO ASIC, already developed for the ALICE TPC for data digitization and readout. The system infrastructure, as buses, power and cooling, can also make use of the same concepts as the ALICE TPC system. The group provided detailed speciﬁcations for the design of both the FEE and TRU units as a proposal for PHOS electronics to be built in 2004.

A four-channel TRU emulator was built, using the AROC PCI card and its embedded FPGA as development platform. By the end of summer 2004, the TRU cards for the coverage of 448 crystals, in parallel with the required FEE cards, will have been designed, aiming for a ﬁrst small PHOS readout and trigger prototype system.

Microelectronics Group (MIC)

The microelectronics group works in close partnership with the LHC collaborations to develop application-speciﬁc, custom-integrated circuits and to integrate them into the electronics systems of the experiments.

ALICE

For the ALICE Time-Of-Flight (TOF) detector the group collaborated with INFN, Bologna on the design of a radiation-tolerant, 8-channel, ultra-fast, amplifier-discriminator ASIC in a 250 nm CMOS process from IBM Microelectronics (USA and France). The requirements for this fully differential front-end chip are a peaking time of 1 ns, a jitter of 10 ps and a time-walk below 25 ps. During 2003 the final prototype was successfully tested. The submission of the engineering run is scheduled for early 2004 and production for the end of 2004. Also for the TOF detector, the group launched a production run of 48 wafers containing the final version of the High-Precision Time-to-Digital-Converter (HPTDC) chip.

For the ALICE pixel detector, the group helped prepare and staff a successful heavy-ion test-beam run in October 2003. Considerable effort was invested in stabilizing the ALICE ladder bump-bonding at VTT, Finland following the delivery of in-spec thin ladders. A ﬁnal version of the analog pilot chip was designed and tested. Support was provided to integrate the analog pilot in the ladder readout MCM.

130 Experimental Physics Division ATLAS

The DTMROC-S chip for readout of the ATLAS straw tube detector (TRT), designed in the 250 nm CMOS process using a radiation-tolerant layout method, passed a production readiness review and the full production of 50 000 parts was completed. Also for the TRT, parametric testing of the DMILL production wafer lots for the very front-end ASDBLR chip was carried out in order to predict the production yield.

The group supported production of the Semiconductor Tracker’s (SCT) front-end chip (ABCD3T) by monitoring the yield of wafers delivered by the foundry (ATMEL, France) and providing quality assurance by X-ray irradiation of the production lots. Assistance was given to the ATLAS SCT collaboration by performing statistical analysis of the performance of the different DMILL production lots.

The group contributed to the technical co-ordination of ATLAS by monitoring and advising on radiation- hardness-assurance procedures for electronics components. Several irradiation campaigns were organized for LHC experiments in coordination with the LHC machine radiation working group.

The group participated in the study of Electromagnetic Compatibility (EMC) issues, in particular the analysis of cavity resonances in the mechanical support structure for the pixel detector. Contributions were made to the grounding and shielding schemes in the inner detectors (Pixel, SCT and TRT) and the integration of the individual subdetector grounding schemes.

CMS

The group contributed to the construction of the CMS tracker, electromagnetic calorimeter (ECAL) and preshower detectors by developing a common FEC board (i.e. the external, slow-control master). The design of the optical PCI version was ﬁnished and a ﬁrst batch of 12 boards was distributed. A VME version is being prototyped. A substantial number of other boards were produced to support beam-tests, module measurements, and characterization of the electronics parts used in the tracker. The architecture of the ECAL electronics was revisited and a new design was produced using the same ASICs initially developed for the Tracker’s slow control and timing system. The use of these ASICs is also being extended to the muon RPC chambers and probably to the pixel detector, with substantial savings in cost and maintenance.

A 12-bit 40 Msps quadruple analog-to-digital converter ASIC was prototyped for the ECAL detector in collaboration with Chip Idea (Portugal). It has the same characteristics as a state-of-the-art commercial part, but it is designed with radiation-tolerant techniques in 250 nm CMOS, consumes less power, and is very competitive in price, allowing a substantial cost reduction of the ECAL electronics. The ﬁrst prototype was found to be very close to the design speciﬁcations. A second design iteration was submitted for prototype manufacturing and is expected to be available during early 2004.

The production of 50 wafers of radiation-tolerant 800 Mbit/s and 1.6 Gbit/s serializer chips (GOL) for detector readout over optical links was completed and the test equipment was built in collaboration with Fermilab. A crystal-based, low jitter Phase-Locked-Loop chip (QPLL) for use in ATLAS, CMS, and LHCb was fully characterized and submitted for production.

Experimental Physics Division 131 For the Preshower detector the PACE3 front-end chip set, shown in Fig. 1, was prototyped in IBM Microelectronics’ 250 nm CMOS technology and was successfully tested. The measured pedestal non- uniformity of the analog pipeline was 0.5 mV r.m.s., and the noise for 50 pF pad capacitance was ENC = 3000 electrons r.m.s. for a peaking time of 23 ns. The measured linear dynamic range of the circuit is equivalent to 11-bit resolution.

Fig. 1: Microphoto of the PACE3 chip set; on the left side is the 32-channel analog front-end chip (Delta), and on the right the PACE_AM, a large dynamic range analog pipeline and multiplexer.

The CMS muon group received the first production batches of the HPTDC ASIC for the muon drift chambers. The same chip is configurable for application in the ALICE TOF detector (see above). The group is also organizing the supply of these HPTDCs to other scientific institutes and to external instrumentation companies.

LHCb

One group member continued to coordinate electronics for the LHCb Collaboration. Following the successful encapsulation of the 10 MHz ALICE1LHCb chip in an HPD tube, two new tubes were produced with the 40 MHz LHCBPIX1 chip. A considerable effort was put into the optimization of the high-lead- content (high-melting-point) bump bonding process, which led to the successful production of these two tubes. The excellent performance of these tubes in a test beam and delivery of a further 20 working assemblies from VTT convinced the LHCb Collaboration to select the pixel-HPDs as the RICH photon detector.

NA60 and TOTEM

Support from the group and the ALICE pixel team enabled the NA60 experiment to complete its silicon pixel detectors in time for the 49In beam run of September. In particular, bump-bonding of assemblies was a major issue and one member of the group acted as technical coordinator for that effort. Support was given for the use of Active Feedback Preampliﬁer (AFP) chips in the NA60 Beamscope.

132 Experimental Physics Division For TOTEM the group developed a 128-channel chip (VFAT) to read out silicon microstrip detectors and provide inputs to the TOTEM trigger. Electronics support and hardware design and fabrication were provided for the evaluation of different silicon detector prototypes in a beam test. The group participated in writing the TOTEM Technical Design Report for submission to the LHCC in January 2004.

LHC Machine

Difﬁculties with the procurement of a radiation-hard chip for readout of the pressure, level, and temperature sensors of the LHC dipole magnets required a rapid redesign of the chip in 250 nm CMOS technology using the radiation-tolerant layout method. For this work a CERN microelectronics engineer supervised three to four engineers from a local company (C4I, France) and the Rhône-Alpes region. The redesign was completed within ﬁve weeks and submitted for manufacture in October. The prototype chip is expected back from fabrication in mid January 2004.

Medical Imaging

A two-fold increase in the yield for the Medipix chip was obtained after successful resolution of a production yield problem that was also encountered by some of the large LHC chips. A contract was launched with MCNC (USA) for provision of bump-bonded detector assemblies which started to arrive in numbers towards the end of 2003. In the context of a technology transfer agreement, engineering resources were obtained to complete a redesign of a production grade Medipix2 chip.

Microelectronics Support, Common Projects, and New Developments

On behalf of the LHC community the group continued to provide technical and administrative interfaces to IBM Microelectronics (USA and France) for manufacture of wafers in the 250 nm CMOS process. In 2003 the group organized 3 multi-project wafer submissions, 10 engineering runs and 10 production runs involving as many as 15 external institutes. Extended collaboration took place with the manufacturer’s engineers to understand and successfully resolve a yield issue that had appeared in several large designs.

The production of the TTCrx ASIC for the common Timing, Trigger and Control (TTC) system employed by the four LHC experiments was completed with about 20 000 chips packaged, tested, and distributed to the users.

In preparation for the future, the group organized and managed a number of meetings with major laboratories in Europe and in the USA in order to plan a coordinated transition to next-generation microelectronics technologies. In this context a number of demonstrator chips were prototyped in a 130 nm CMOS process and gave promising results, including evidence that future, deep-submicron technologies tend towards an enhanced intrinsic radiation tolerance.

The collaboration with STMicroelectronics (Italy) on the development of radiation hardened voltage regulators for the LHC was continued. A production batch of the L4913 positive regulator was completed and, with assistance from the CERN Stores, 50 000 parts were distributed to LHC users. The ﬁnal prototype of the L7913 negative regulator was characterized and found to fulﬁl the radiation hardness requirements. Volume production of the L7913 is planned for early 2004.

Experimental Physics Division 133 In collaboration with Brunel University and the universities of Hawaii and Stanford, beam test measurements were made of ‘3D silicon detectors’ at room temperature. With their ‘edgeless’ property, these 3D detectors can be considered good candidates to instrument the Roman Pots planned by the ATLAS and TOTEM collaborations.

In collaboration with the Institute of Microtechnology at the University of Neuchâtel, prototypes of Thin Film on ASIC (TFA) sensors were built by depositing a layer of hydrogenated amorphous silicon directly on the surface of a readout chip. These TFA sensor devices were successfully characterized with radioactive sources, and in a muon beam. TFA detectors were also tested to very high ﬂuences in the NA60 49In heavy-ion run without showing any radiation damage. A radiation-hard TFA beamscope has been designed and will be tested in the NA60 proton run in 2004.

Electronic Systems Support Group – ESS

During the course of 2003, work on common projects continued and a reorganization of the Electronics Pool was initiated following a detailed review of its technical and ﬁnancial aspects.

Common and Joint Projects

Subracks (Crates) for LHC

Following the placement of a contract for the supply and support of subracks for LHC, prototype tests were completed and the first annual (2003) release order made for some 140 complete subracks for use by all four LHC experiments, as well as for the AB Division Controls Group. Following the delivery of the first production batch, the subracks were subjected to a detailed test and a number of corrections and modifications agreed with the manufacturer. Subsequent batches were given a short, functional test before being dispatched to the final users. A database of all information concerning the subracks was constructed and will be made accessible to the end-users.

The electromagnetic compatibility performance of the subrack power supplies was the subject of detailed tests by ST-EL group, the results of which showed that the subracks perform well within the required limits and are entirely suitable for use in the LHC.

Further investigations into a practical mounting for remote, water-cooled power supplies were made. Mechanical alignment jigs were developed to permit easy checks on production crates.

Preparation for the 2004 release order scheduled for the end of 2003 was started with technical discussions being undertaken with users in the LHC experiments.

The development of an automatic power supply test system was begun with investigations into an appropriate software environment.

134 Experimental Physics Division Rack Control

The rack control project was pursued during 2003, with major progress on the design and implementation of the rack monitor system. A design review of the overall rack control system and a production readiness review of the detailed design of the rack monitor were held. The design review resulted in a proposal for reinforced coordination of the rack control project, particularly between the experiments and ST-EL and EP- ESS groups. The coordination effort, once approved by the LHC Technical Coordinators, the ST-EL and EP- ESS group leaders, was delegated to ESS group.

The Production Readiness Review made a number of suggestions, all of which were implemented in a second prototype monitor system. Tests were made to prove the magnetic ﬁeld tolerance and radiation tests were planned. Tests of the smoke detector were made in collaboration with ST-MA group.

The prototype monitor system was integrated into the prototype rack turbine chassis and discussions were held with SPL Division on the procurement strategy of the ﬁnal assembly. Steps were taken to procure long lead-time items.

Radiation- and Magnetic-Field-Tolerant Power Supplies

In the context of a joint activity with the four LHC experiments, detailed discussions were held with potential users and suppliers of power supply systems to agree on a suitable architecture for radiation- and magnetic-ﬁeld-tolerant power supplies for use in detector power supplies and subracks.

ESS group carried out magnetic-ﬁeld and radiation-tolerance tests at CERN and at PSI on candidate low- voltage power supply systems and various components. The magnetic ﬁeld tests were presented at the LECC Workshop in Amsterdam.

TTC Support

After discussions with the four LHC experiments and the accelerator controls group, the production of 110 TTCvi and 15 TTCxv modules was started. These are expected to be the last batches of the respective types of modules.

In the case of the TTCex, TTCtx, TTCrq and TTCoc it was not possible to produce all the modules required for the operation of the experiments (including spares) in one batch as not all experiments could give ﬁnal numbers. Therefore only the modules required for 2004 have been ordered: 51 TTCex, 11 TTCtx, 18 TTCoc16, 10 TTCoc32 and 150 TTCrq. It is planned to order a ﬁnal batch of each type before the end of 2004.

Radiation tolerance tests were made to choose a suitable optical receiver; the results of which were presented at the LECC Workshop in Amsterdam.

Experimental Physics Division 135 Single Board Computer Support

In 2003 a total of 61 VP110 modules were ordered from Concurrent Technologies for the ATLAS experiment (43 modules) and the Electronics Pool (18). In late 2003 ALICE also decided to use the VP110 for most of their VMEbus installations.

Gamma Irradiation Facility (GIF)

The cabling of the GIF has been reduced to an unacceptable state over the years and an inspection by the management led to a demand for a clean-up. Although plans were made for the cabling to be modiﬁed, it was difﬁcult to arrange because of the heavy demands and tight schedules of the experiments. However, work was done throughout the year to improve the cabling situation: a team provided by the DSO did most of the work. A major clean-up of the cabling is scheduled to take place after the beam run in 2004.

There were major problems with the control system during the year, when the Vobis computers failed. All computers were replaced with Elonex computers and at the same time the most recent versions of both the operating systems and the PVSS control system were installed. This has led to an improvement in long-term stability.

The strongest demand on the GIF was made by the RPC tests on recycling gas systems. For this, recycling gas systems with facilities for sample taking were installed in the GIF gas area. The appointment of the ESS GIF project leader as GLIMOS for the GIF, and the insistence on the inspection of experiments after installation have led to an enormous improvement in the standard of installation of the experiments.

Work has started on proposals for a new GIF facility, and discussions have been held with the experts of the various experiments. Visits have also been made to the North Area to look for a suitable place to install a new GIF.

Electronics Pool

Operations

In order to permit an increased level of support from AS Division, to reduce the need for local database expertise within ESS group as well as the implementation of equipment reservation via EDH material requests, a successful effort was made, in collaboration with AS Division, to move the Pool’s instance of the BAAN database management system to that used by the CERN Stores. The Pool’s operations staff followed a short training on the use of the BAAN user interface for the preparation of statistical reports, etc.

A major effort was made to make documentation for all Pool equipment in electronic form available from the Electronic Pool’s Web site. A Web-based automated system was developed and installed to aid the recoding of the delivery and return of Pool instruments; in particular to ensure that the budget holders are informed by e-mail of any such movement.

Following the guidelines recommended by EPTAB, equipment was purchased for a total of 2 MCHF.

136 Experimental Physics Division EPTAB

The Electronic Pool Technical Advisory Board (EPTAB) held three meetings during the course of 2003. Discussions were held on the technical proﬁle of the Electronics Pool, as well as on the choice of a number of new items. Overall, it was recommended that the Pool reduce the number of types of instruments and modules, concentrating on a range of coherent sets of instruments targeted at speciﬁc areas of application.

New Financial Conditions

Proposals for new ﬁnancial conditions were made to EP Division management and the CERN Research Director. These included a simpliﬁed method of establishing rental fees based on the real cost of each type of equipment, as well as setting the resale value of equipment which is also used in case of compensation for loss or major damage. The proposals were approved and their implementation started.

Other Activities

Updating Test Procedures

A considerable number of test procedures based on obsolete OS-9 software were ported to a modern Linux-based VMEbus SBC.

A PHP-based Web-to-database interface for the distribution of board IDs for VMEbus and PCI cards was developed.

Contracts and Administration

In collaboration with SPL Division, ESS provided support to ATLAS and CMS for Market Survey and Invitation to tender procedures.

Experiment Support

A member of ESS provided systems assistance to the ALICE DAQ group, including on-call support. In addition, a member of ESS worked on the design of the ATLAS DAQ system and is heavily involved with ATLAS test beam support.

A member of ESS group is collaborating with EP-ATE group on aspects of the design of the TRT TTC module.

Test Facilities

The Climatic Chamber facility supported by ESS for general use by design groups was modernized with the purchase of a new chamber. This is equipped with a split VME64x backplane with additional space for other equipment. The chamber and the VME64x power supplies may be controlled remotely and are available for the temperature testing of equipment. In addition, a fully instrumented 9U VME64x crate is available for tests involving dynamic-supply-current variations.

Experimental Physics Division 137 Software Development and Users’ Support

Software Design for Experiments Group (SFT)

The mandate of the SFT group is to design, develop and maintain common software for the physics experiments in close collaboration with the EP experimental groups, the CERN IT Division and collaborating HEP Institutes. The majority of the group is directly involved in projects organized as part of the Applications Area of the LHC Computing Grid Project. In addition, several group members have direct responsibilities in the software projects of the LHC experiments, fulﬁlling key roles such as ‘software architect’ and project leadership for the various data processing applications. This report focuses on the work of the group in the Applications Area of the LCG project.

The Applications Area develops and maintains that part of the physics applications software and associated infrastructure that is shared among the LHC experiments. The scope includes common applications software infrastructure, frameworks, libraries, and tools; common applications such as simulation and analysis toolkits; grid interfaces to the experiments; and assisting the integration and adaptation of physics applications software in the grid environment. The work of the applications area is conducted within projects. As of December 2003 there are ﬁve active projects: software process and infrastructure (SPI), persistency framework (POOL), core libraries and services (SEAL), physicist interface (PI), and simulation (SIMU).

The SPI project provides a set of basic services for the various phases of the software development lifecycle (coding, testing, delivery, verification etc.). Guidelines for coding and design have been agreed and a CVS repository for each LCG project established. SCRAM was chosen as LCG’s configuration and release manager and an automatic build system, NICOS, integrated in the release cycles for POOL and SEAL. A service to provide ~50 third-party software installations in the versions and platforms needed by the LCG projects has also been developed. A Web-based ‘project portal’ based on the Savannah open source software has been deployed in production. It integrates a bug tracking tool with many other software development services. This service is now in use by all the LCG projects and by more than fifty projects in the LHC experiments. SPI has deployed an automatic system to generate ‘code documentation’ on the Web based on Doxygen, as well as LXR and ViewCVS. A ‘workbook’ organization and infrastructure for project documentation was developed and deployed and is evolving into a comprehensive and complete documentation of all the LCG projects. SPI has deployed a ‘testing framework’ to standardize the way projects perform unit and regression testing (CppUnit, PyUnit, Oval) as well as memory leak finding (Valgrind). In order to have the infrastructure used effectively by the LCG projects, SPI assigned resources to help the other projects in a practical way and perform a ‘quality assurance’ function by actively encouraging LCG projects to use the SPI development guidelines and testing facilities. SPI is also organizing training for the LCG projects including tutorials on ROOT, SCRAM and Savannah. SPI has added a service to allow easy downloading and local installation of the LCG software and all needed external software.

The purpose of the POOL project is to develop the persistency framework for physics applications at the LHC. The current focus of the POOL effort is support for the integration and deployment of POOL in CMS and ATLAS as the mechanism for production event storage. The ﬁrst important validation milestones were met on time with the acceptance and deployment of POOL by CMS for its pre-challenge simulation production and a steady production rate of millions of POOL events per week has now been achieved. ATLAS also

138 Experimental Physics Division delivered its ﬁrst integration of POOL into ATHENA during the year. Both ATLAS and CMS found the integration of POOL and SEAL to be more work than they expected and therefore the project has now assigned extra effort in order to ensure that project software is integrated and validated promptly in the future.

SFT group members also provide key core development and management effort for ROOT, which is a general-purpose, object-oriented framework that implements software for managing the persistency of objects and for supporting interactive data analysis and visualization. ROOT is widely used by running experiments in many HEP labs around the world and a signiﬁcant effort continues to be invested by us in supporting this very large community of ROOT developers. ROOT is also used to implement vital parts of Applications Area software such as the object streaming technology of POOL. This year further development of ROOT components has been made to deliver and reﬁne key functionality needed by POOL. Group members are also contributing to GUI and graphics development, documentation, and a ROOT-Apache module supporting distributed use of ROOT based on embedding ROOT functionality in Web pages.

The SEAL project aims to provide the software infrastructure, basic frameworks, libraries and tools that are common among the LHC experiments. The project addresses the selection, integration, development and support of foundation and utility class libraries as well as the development of a coherent set of basic framework services that will facilitate the integration of LCG and non-LCG software such that coherent applications can be easily assembled. Components that have already been made available in the public release include foundation libraries (based on classlib), a plug-in manager, a prototype of the Minuit minimization package re-engineered in C++, models and tools for implementing the LCG object dictionary, and scripting services based on Python. These components are already being used by other LCG projects, in particular by POOL. Several mathematics-related packages (CLHEP, GSL, Blas, Lapack) have been installed as part of the overall support for external packages. Python courses have been prepared and delivered to more than 70 people as part of the CERN technical training programme. The ﬁrst implementation of the SEAL component model for the Framework sub-system has been released and user feedback is eagerly awaited.

The PI project covers the interfaces and tools by which physicists will use the software. The project has focused on providing an abstract interface (called AIDA) to analysis tools (such as the definition, filling and plotting of histograms) to allow interoperability between different implementations. A first implementation has been released based on ROOT histograms and plotting using the ROOT canvas. Issues related to distributed analysis will be addressed in the context of a new LCG project (called ARDA).

The Simulation project (SIMU) involves major efforts in a generic simulation framework, the simulation engines to be used in it (GEANT4 and FLUKA), the validation of physics models used in these engines, and the use and integration of event generators. This project has been very successful in bringing together those developing specialized simulation software components with those physicists working on simulating the real LHC detectors.

– The GEANT4 subproject comprises a worldwide collaboration of physicists, and SFT group provides much of the core development and infrastructure support for the project. This year has seen two major releases of the GEANT4 software including new functionality (such as a consolidated version of ‘cuts per region’), as well as improvements in stability and performance. In hadronic physics, a new version of physics lists was released providing for the needs of CMS 2003 simulation production, test-beam comparisons in ATLAS and CMS, and the LCG thin target validation. The expanding testing uncovered a number of bugs and deficiencies, and the creation of fixes and accompanying testing were significant undertakings.

Experimental Physics Division 139 – The Physics Validation subproject is very active and into a regular programme of monthly meetings gathering participants from all the LHC experiments and simulation projects. The software infrastructure has been set up to compare FLUKA and GEANT4 with data for simple geometries and ‘single interactions’. First studies of 113 MeV protons on thin Al targets, and comparisons of both packages with Los Alamos data, have been performed. The study of double differential cross-sections for (p, xn) at various energies and angles has been completed. Radiation background studies in the LHCb experiment, aiming at comparing G4/FLUKA/GCALOR, have started. Physics validation of FLUKA using ATLAS Tilecal test-beam data is also in progress. Comparisons of test-beam data with GEANT4 have concentrated on hadronic physics with calorimeters, both in ATLAS and CMS, as well as with special data collected with the ATLAS pixel detector. One interesting result is that corrections to the pion cross-section in GEANT4 have yielded signiﬁcant improvements in the description of the pion shower longitudinal shape in the LHC calorimeters.

– The Generator Services subproject has initiated a central code repository for generators and common generator tools (GENSER) in order to provide quick releases to the experiments, decoupled from large generator library releases. It contains all the top priority packages: HERWIG, HIJING, ISAJET and PYTHIA. Binary distributions and maintenance are being provided for LCG supported platforms.

Users’ Office Group (UO)

The Users’ Office was founded in 1989, following the recommendations of the CERN Review Committee as laid out in the Abragam report, its mission being to help the scientific users in carrying out their research at CERN in the best possible conditions. In more concrete terms, the Users’ Office should

– inform the users about CERN and the services it provides;

– inform the CERN management about the users, and make the CERN services more aware of, and therefore more responsive to, users’ needs;

– provide some direct support and non-bureaucratic help in getting things done.

The first place a new user in EP Division sees – or is at least supposed to see – is the Users’ Office, and because it must be easy to find, it is located in Bldg. 61 and occupies a central place at CERN, close to the bank, post office, and restaurant.

Every new user attached to EP Division – a person who is not employed by CERN but by an institute in Member and Non-Member States coming to work on an experiment – registers at the Users’ Office, fills in and receives his residence papers, obtains his CERN access card and gets advice. The staff takes care of visas and letters of invitation, and it will also help with any official document that seems too complicated to fill in. The aim is to ease the users’ lives, not to complicate them. The staff tries either to solve the problem on the spot, or, if not, find the right person to talk to. The staff must respect the rules laid down by the Organization and the Host States concerning the registration of users, even though their requests for documentary evidence are not always appreciated.

A signiﬁcant amount of time is spent answering questions by phone, e-mail, or in person. Eleven people, several of them working part-time only, are constantly dealing with matters that concern CERN users. Their days are unpredictable; their day-to-day work covers a wide range of subjects.

140 Experimental Physics Division Registration is only one part of the administrative business. CERN has users (6,362 in total at the end of 2003) who come from Member States and from Non-Member States, covering more than 80 different nationalities. All these people have papers that are valid for one or two years, respectively, consequently there is a regular traffic into the Users’ Office for extensions and modifications. In order to avoid possible administrative difficulties, a system was set up to warn users via e-mail when their contracts are about to expire. It is very difficult to predict in the morning how many people are going to visit the Office during the day, although there is a clear peak shortly after the warning e-mails have been sent, during the major experiments’ collaboration weeks, or in the summer months.

The Users’ Ofﬁce is the secretariat for the Advisory Committee of CERN Users (ACCU), which discusses many topics relevant for making users’ stays at CERN agreeable. Amongst other things ACCU urged the CERN Management to provide both more ofﬁce space and more beds for the users – and Bldg. 40, Bldg. 39 and the extension to Bldg. 38 are the results!

The Users’ Ofﬁce, together with the experiment secretariats, is responsible for the maintenance of the data in the ‘Grey Book’ (Experiments at CERN). Two part-time staff run the Grey Book secretariat, registering new experiments, updating the abstracts, and changing the status as they become active or are completed. They also maintain the data for those experiments which do not have a secretariat at CERN, in addition to their main registration duties in the Ofﬁce.

The Websites for the Users’ Ofﬁce and ACCU were designed and are taken care of here. The staff also takes care of the PCs that await clients in the corridor outside the Users’ Ofﬁce, and there is a selection of European daily newspapers in the reading room (and on the Website) as well as a phone for local calls.

Information about CERN, Member States and Non-Member States, Geneva, the local area of France, are available on the Web and/or on a self-service basis. The CERN Guide for Newcomers was produced in the Ofﬁce and a copy is given to users at registration.

Another important part of the Users’ Office universe is the ‘Office in charge of relations between CERN and Non-Member States’ and more specifically the former Eastern Block. This office is responsible for allocating funds for these Non-Member States. The staff speaks Russian and uses it every day because everything happening at CERN that is somehow connected to Russia or one of the other states goes through its hands. They are the interface between the people from the experiments – group leaders, spokespersons etc. – and the Russian institutes. They are well informed about the current political situation in the countries they deal with, they keep contact with them also when there is a crisis, and they help towards solving problems that may occur in the supply of components and services.

Other important tasks handled by the Ofﬁce include: the maintenance of the Institutes list, with the collaboration of the library and HR division; the provision of User statistics to the directorate, the Press Ofﬁce, the Non-Member States representatives and others; the organization of workshops to train new experiment secretaries on the procedures for using the PIE application to maintain their experiment information, which appears in the Grey Book.

Experimental Physics Division 141 Space Management and Infrastructure Group (SMI)

The Space Management and Infrastructure Group (EP-SMI) was formed in 1998 with the aim of gathering people from various existing services concerned with the allocation of space, ofﬁce removals, furniture, maintenance, equipment storage and User facilities into a single operating unit.

A particular need in the early years of the group was to rapidly liberate and renovate experimental hall space so as to provide assembly areas for sub-detectors of the LHC collaborations. This programme, which cost some 8 MCHF, was considerably more economical than the construction or rental of new assembly halls: it has also resulted in a more rational approach to storage in the research sector.

The EP-SMI group is responsible for the management and allocation of 45% of all office and laboratory space in CERN and 25% of all assembly and experimental hall space: a total floor area of some 98 000 m2. It maintains the relevant CERN databases for space allocation, locks and keys (GESLOC, GESCLE), as well as updated annotated floor plans of office occupation. Its client base amounts to 77% of the total registered personnel on site – staff, contractors, and Users.

The 7000-strong CERN User community presents a particular challenge in that individuals are not always on site and are at times difﬁcult to contact – it is an ever-changing population with research students and staff completing assignments or changing institutes. Presence at CERN varies considerably depending on the time of year and the different phases of an experiment – preparation, test beams, assembly, installation, data taking and analysis. A single university group may often be preparing one experiment, taking data in another, and analysing a third. It is, nevertheless, deemed important to group people from different institutes, who are working on similar aspects of an experiment, in the same geographical location. CERN Users have a right to expect reasonable facilities and working conditions when they are on site.

A major preoccupation has been to negotiate the release of space, principally that allocated to the LEP and neutrino collaborations, and re-assign this to the growing LHC community. To accelerate this migration, the EP Division Leader set up a small Space Task Force (STF) that has advised the SMI group on policy matters and established guidelines for the future. The STF chairman has represented the Division on space matters in interdivisional negotiations and in the drafting of Memoranda of Understanding. The STF and SMI work closely with the Resource Managers and Secretariats of the major collaborations, the Regional Secretariats, and the Users’ Ofﬁce. The SMI group leader represents the Research Sector on the Site Committee and the General Services Technical Committee (GSTC).

The principal motivation of the SMI group is to provide services to the Division and the User community by way of logistics and facilities support. It manages all aspects of office moves, keys, telephone transfer, office furniture, refurbishing, small building work, equipment installation, and the provision of archive and medium-term storage space. It also assists in the installation and maintenance of conference room projectors and can provide mobile and multi-band telephones for short-term use. Some offices are available for reservation under our ‘Bûrotel’ scheme for short-term occasional visitors and a centre for retired ‘honorary’ staff with a continuing scientific activity is in preparation. SMI is also responsible for temporary barracks, containers and control rooms in or near experimental areas: in order to improve the use of space, it coordinates larger, building renovation projects in collaboration with ST Division and outside contractors.

142 Experimental Physics Division Particular innovations have included the use of temporary structures for economical storage, improved solutions for assembly hall use, recuperation/recycling and high density archiving; we have also piloted similar schemes for other divisions. Our progressive introduction of ‘hotel type’ coded door locks using CERN access cards will result in substantial long-term cost savings, improved security and control.

Mobility services provided by SMI include a pool of some 130 vehicles for short- or long-term hire to User groups: the cost is around 15 CHF per day (+ fuel charge) and vehicles may be used between a local place of residence and the CERN sites. Bicycles are also a popular way of getting around the site: SMI maintains a pool of around 250 bicycles, available for limited duration on a ﬁrst-come-ﬁrst served basis: there is no charge but a deposit of 100 CHF is required against possible damage. The group manages CERN vehicles for the division and has a small pool for short-term loans and one or two special vehicles for invalid drivers. It also issues the Job Orders (Ordres de Mission) required by all drivers for journeys outside the CERN circulation perimeter and to places of residence. The Chairman and Secretary of the CERN Vehicle Committee (CVC) are both from the SMI group.

The SMI Reception Desk is in Bldg. 124 where all our services are based: details can also be found on the SMI Web site via the EP Division Home pages. All requests, even within the group, are routed through our job registration and follow-up system SMILES (SMI Logistics Entry System). Other software products developed within the group include a sophisticated vehicle reservation system that includes the generation of hire contracts and vehicle/driver tracing: direct client billing is being developed. All speciﬁc databases and tools, including those for space management, are held on the SMI group server.

Since January 2002, a number of our activities are outsourced to a Field Service Unit: the contract places great emphasis on a regularly monitored ‘Quality Service’ but does not compromise the personal contacts that have always been a feature of the SMI group. This contract has served a model for many of the Field Service Contracts now being established throughout CERN.

Experimental Physics Division 143