124 Annual Report 1999

The work has also been started on the design and Two electronics engineers from the 3rd department the simulation of the whole alignment system for the of the Institute are involved in the design an tests of eleven drift chambers of the outer tracker. the Readout Supervisor unit for the Data Acquisition system of the LHC-b experiment.

Bending Plant* Muon Detector Shield

I I I I I I I I I I I I I I I I I I I I

0 5 10 15 2[m] M Fig. 1 The LHC-b detector seen from above (cut in the bending plane). The tracking chambers are Labeled Tl - Tl 1, the muon chambers are labeled Ml - M5.

PL0001546 6.15 The ALICE Experiment by D.Czerwinski, A.Deloff, K.Karpio, S.Kozak, M.Koztowski, L.Lukaszek, H.Malinowski, T.Siemiarczuk, G.Stefanek, L.Tykarski and G.Wilk for ALICE Collaboration

ALICE (A Large Ion Collider Experiment) is an organization and planning milestones of the specific experiment at the Large Collider (LHC) detector. optimized for the study of heavy-ion collisions, at a Below we list main physics goals of the detectors centre-of-mass energy -5.5 TeV per . The presented in the published f 1-5] TDR's: prime aim of the experiment is to study in detail the 1. The photon spectrometer PHOS [1J provides behaviour of nuclear matter at high densities and unique coverage of the following physics topics: temperatures, in view of probing and chiral symmetry restoration. • thermal and dynamical parameters of the initial phase of the collision, in particular the initial The detector consists essentially of two main temperature, via direct single photons and di- components: the central part, composed of detectors photons; mainly devoted to the study of hadronic signals and • as a probe of deconfinement, dielectrons, and the forward muon spectrometer, devoted to the study of quarkonia behaviour in dense studied via high pi n°; matter. A major technical challenge is imposed by a • signals of chiral-symmetry restoration. large number of created in the collisions of In addition, the neutral- transverse-momentum ions. There is a considerable spread in the spectra and Hanbury-Brown and Twiss correlations currently available predictions for the multiplicity of will provide important constraints on the dynamical charged particles produced in a central Pb-Pb evolution of the hadronic phase, up to the freeze-out collision, The design of the experiment was based on stage. the highest value, 8000 charged particles per unit of 2. The Zero Degree Calorimeter ZDC [2]: rapidity, at midrapidity. This multiplicity dictates the In heavy-ion interactions, the event-by-event granularity of the detectors and their optimal distance determination of the collision's centrality, which is a from the colliding beams. major rote of the ZDC, plays a basic role; it is used at Five Technical Design Reports (TDR) have been the trigger level to enhance the sample of central prepared, submitted to and approved by the collisions and, more generally, to estimate the energy density reached in the interaction. It is therefore CERN Committee. Each of important to have a detector which can provide a fast the TDR's presents detailed design considerations, and reliable characterization of the event geometry. simulations of physics performance as well as the DEPARTMENT OF HIGH ENERGY PHYSICS 125

3. The Inner Tracking System ITS [3]: study of the observables Ny and Ny/Nci, with full The ITS will contribute to the track reconstruction azimuthal coverage. by improving the momentum resolution obtained by 5. The Dimuon Forward Spectrometer DFS [5] : the . This will be beneficial Hard, penetrating probes, such as heavy- for practically *J1 physics topics which will be quarkonium states, provide an essential tool to study addressed by the ALICE experiment. The global event the earliest and hottest stages of nucleus-nucleus features will be studied by measuring the multiplicity collisions because they are expected to be sensitive to distributions and the inclusive spectra. For the the nature (i.e. confined versus deconfined) of the study of resonance production (p, w and (f>), and, more strongly interacting matter created in these reactions importantly, the behaviour of the mass and width of on short distance scales and at early times. The large these mesons in the dense medium, the momentum binding energy of the quarkonium ground states JP¥ resolution is even more important. We have to achieve and T prevents their dissociation by low-momentum a mass precision comparable to, or better than, the . Gluons confined to are restricted to natural width of the resonances in order to observe rather low momenta, as it is known from the parton changes of their parameters caused by chiral distribution functions measured in deep-inelastic symmetry restoration. Also the mass resolution for scattering. As a result, the cross-section for the heavy states, like D mesons, JAJf and T, will be better, dissociation of ground-state quarkonia by hadronic thus improving the signal-to-background ratio in the collisions is strongly damped. In contrast, a measurement of the open charm production, and in the deconfined medium, even at comparatively low study of heavy-quarkonia suppression. Improved temperatures, contains sufficiently hard gluons. Hence momentum resolution will enhance the performance in the dissociation of quarkonium ground states is a clear the observation of another hard phenomenon, the jet evidence of deconfinement. production and predicted jet quenching, i.e. the energy loss of partons in strongly interacting dense matter. [ 1 ] G.Dellacasa et al., "Photon spectrrometer -PHOS 4. The Photon Multiplicity Detector PMD [4]: ALICE TDR", CERN Report, CERN/LHCC 99-2, Using the measured observables in the PMD, ALICE TDR3,1999 investigations in the following broad topics of physics [2] G.Dellacasa et al., "Zero-Degree Calorimeter - can be pursued: ZDC ALICE TDR", CERN Report, CERN/LHCC • determination of the reaction plane and probes 99-5, ALICE TDR2.1999 of thermalization via studies of azimuthal [3] G.Dellacasa et al., "Inner tracking system - ITS anisotropy and flow; ALICE TDR", CERN Report, CERN/LHCC 99- • critical phenomena near the phase boundary 12, Alice TDR4,1999 leading to fluctuations in global observables [4] G.Dellacasa et al., "Photon multiplicity detector - like multipicity, mean transverse momentum PMD ALICE TDR", CERN Report, and pseudorapidity distributions; CERN/LHCC 99-32, Alice TDR6,1999 • signals of chiral-symmetry restoration (e.g. [5] G.Dellacasa et al., "Dimuon Forward disoriented chiral condensates) through the Spectrometer - DFS ALICE TDR", CERN Report, measurement of charged-particle multiplicity CERN/LHCC 99-22, Alice TDR5.1999 (yVch) in a common part of phase space and Illlllllllll pi 0001547 6.16 The COMPASS Experiment at CERN by O.Grajek, K.Kowalik, K.Kurek, A.Mielech, J.Nassalski, E.Rondio, A.Sandacz, W.Wislicki

COMPASS, which stands for Common Muon and hadrons with high p-r- In another proposed method to Apparatus for Structure and Spectroscopy, is "probe" gluons in the nucleon we will use the the fixed target experiment located in the North Area diffractive production of vector mesons. The of the SPS accelerator. The programme of the project experiment will be performed using high-energy is divided in two parts with different beams. For this polarised virtual photons from an intense polarised purpose the muon beam line was modified to transport muon beam impinging on a double cell polarised solid hadrons with energies up to 300 GeV as well as state target. The accuracy for AG/G is predicted to be muons. in range 0.05 - 0.1, depending on the tagging method. The main aim of the COMPASS programme with The experiment will also provide high statistics data the muon beam is the determination of the for semi-inclusive muon scattering, the spin structure polarisation in the nucleon: AG/G. It will be obtained function g] and the transverse structure function ht. from measurements of the spin asymmetries of cross Also a broad program with the hadron beam will sections for photon-gluon fusion, which will be tagged be performed. The main subjects are as follows: either by open charm production (mostly D° mesons) studies of charmed hadrons, spectroscopy of light or by production of pairs of oppositely charged systems and glueballs and investigation of the