Warsaw University's Auditorium Maximum provided the location for the parallel sessions Warsaw conference of the 1996 Rochester conference.

n recent years, the biennial I "Rochester" International Conference on High Energy has been a festival of the , the 20-year-old set of theories describing particles and forces. Despite early expectations to the contrary, the 28th in this prestigious series, held in Warsaw in July, turned out to be true to form. In 1995, after many years of increasingly accurate measurements agreeing ever more precisely with Standard Model predictions, some small discrepancies appeared. Theoreticians lost no time in invoking explanations involving physics beyond the Standard Model. The most popular of these is , a theory linking particles and forces which introduces a new "supersymmetric" partner for each ordinary particle. The atmos­ phere was charged with anticipation

for new physics. But by the time the on the so-called Rb from the Andrzej Buras of Munich Technical 1996 Rochester came around, most Aleph and L3 experiments University homed in on CP violation, of the discrepancies had gone away, respectively at CERN's Large the mechanism believed to be

leaving the Standard Model healthier Electron-Positron Collider, LEP. Rh responsible for the apparent absence than it has been for some time. is the fraction of quark-producing Z of antimatter in the Universe. He The mood of the conference was decays resulting in pairs of heavy looked forward to the new precision captured by , b-quarks. Last year, results from measurement of direct CP violation head of CERN's Theory Division, LEP seemed to indicate that this expected soon from CERN's NA48 with his concluding remarks that "The happened far too often (October experiment. Standard Model's health, already 1995, page 1). But supersymmetry Another precision experiment which excellent, keeps improving as it gets provided an explanation. The idea is eagerly anticipated was introduced rid of a little cold, or a small was that the Z can decay into by Warsaw's Stefan Pokorski in his headache." But adding the optimistic supersymmetric particles, which in review of electroweak theory. A new note that "Theoretical belief in turn decay to b-quarks. experiment at Brookhaven will soon supersymmetry appears really The results presented by Tomalin fix the anomalous magnetic moment unshakable, and even contagious and Bertucci are closer to the Stand­ of the muon with the unprecedented towards the experimentalists." ard Model than last year's measure­ precision of 0.35 parts per million, 20 ment. The Aleph result matches times better than CERN's classic precisely at 21.58%, but the new measurement. This important The Standard Model world average is still uncomfortably quantity is a measure of the high at 21.78%. The general feeling pointlikeness of muons, and provides The first hints that the Standard in Warsaw was one of wait-and-see, a powerful test of electroweak theory. Model was on the road to recovery but supersymmetry enthusiasts The Warsaw conference was the came in the parallel sessions when pointed out that the new world first Rochester to welcome the top Ian Tomalin and Bruna Bertucci, both average is exactly what their model quark into the Standard Model's from CERN, presented new results anticipates. heaviest family of particles. Two

CERN Courier, October 1996 1 Warsaw conference

Conference Chairman Andrzej Wroblewski and CERN's Research Director Lorenzo Foa (left) admire conference coverage in Warsaw's newspapers

years ago in Glasgow, top was still unconfirmed. Now, it is perhaps the best measured quark of all, accord­ ing to Rochester University's Paul Tipton, who pinpointed its mass at 175±6 GeV with a production rate around 6.5 pb, a little higher than expected, but not inconsistent with theory. These measurements come from combined data from the CDF and DO experiments at 's Tevatron proton-antiproton collider, and are derived from some 100 pb1 of data corresponding to 500 top- antitop pairs for each experiment. Scott Willenbrock of Illinois continued the top quark theme, looking forward to top physics to come. Since the top quark is so much heavier than the other quarks, he said, there must be something special about it. Top, for example, could have large CP violating decays, and might become the CP laboratory of the future. Top could difference between long-lived and different from that obtained at LEP. even give hints of physics at the short-lived kaons made by the CP- The reasons for this discrepancy are Planck scale where quantum LEAR experiment at CERN. When not yet understood. mechanics and gravity meet. For combined with the experiment's Blondel also had the task of pre­ example, one model of the Higgs studies of CP-violating kaon decays, senting the final Z results from LEP symmetry breaking mechanism, the result carries the reassuring representing seven years of pain­ thought to be responsible for mass, message that the combination of CP staking precision analysis, and the has a second minimum at the Planck with time reversal symmetry, CPT, current state of play with the W, the energy. This model correctly puts appears to be conserved. Zs charged partner. LEP's final the top mass at 173±4 GeV, and Alain Blondel of Ecole Poly- value for the Z mass is predicts a Higgs boson mass of technique pointed out that with the 91.1863±0.0020GeV. Fermilab 135±9 GeV. top mass now measured, the Higgs currently has the best measurement The remaining quarks were covered mass is now the only unknown of the W mass at 80.356±0.125 GeV. by Rochester University's Lawrence parameter in the Standard Model. The LEP2 value from the first few Gibbons who presented a plethora of Since the Higgs mass is highly days of running stands at 80.3 GeV,

2 data on quark mixing. A cornerstone sensitive to sin 0w (the weak mixing with an uncertainty of half a GeV. of the Standard Model is the which links the two components of Summarizing Standard Model Cabibbo-Kobayashi-Maskawa matrix, the electroweak force), that is where physics, Gabriele Veneziano drew whose elements give the probabilities attention should turn, said Blondel. attention to the remaining excursions

of one kind of quark turning into The SLD detector at Stanford's SLC from the Standard Model. Rb is still another. Several new measurements electron-positron collider currently significantly removed from the of oscillation frequencies in neutral B has the most precise measurement prediction, despite the new data.

2 mesons are tightening the constraints of sin 0w obtained by exploiting the There are substantial differences on these matrix elements. Gibbons 80% beam polarization obtainable between SLD and LEP values of

2 also presented the most accurate at SLAC. Their value is sin 0w, and the b-quark coupling

measurement to date of the mass 0.23061 ±0.00047, significantly parameter, Ab, is uncomfortably far

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CERN Courier, October 1996 3 Warsaw conference

Warsaw old town square provided a pleasant place for conference goers to relax after a hard day's work.

Abramowicz. But is the Pomeron real, or is it purely a mathematical tool? By the next Rochester, Abramowicz and Levonian agreed, perhaps we will know the answer. Levonian also spoke of jet multiplici­ ties, an area where experiment and theory have been uncomfortably far apart for some ttme. Theory says that the ratio of multiplicity in gluon jets to that in quark jets should be around 1.8, whereas experiments have suggested a value closer to 1.2. A new analysis by OPAL at LEP, however, gives an experimental value around 1.6, consistent with the theoretical prediction. Gluons could also account for last year's excess of high transverse momentum jets seen by Fermilab's CDF experiment, according to from the Standard Model prediction, don't couple to photons. With LEAR Raymond Brock of Michigan State. he said. Putting all of the new closing down at the end of 1996, the The other Tevatron experiment, DO, Standard Model measurements into immediate future of glueball searches did not see the same effect, which the equations yields a current best will move to Beijing, where the BES led Brock to ask whether the two guess of the Higgs mass at 150 GeV, experiment studies J/psi decays. experiments data sets were beyond the reach of LEP2 but com­ Sergey Levonian of Ecole inconsistent, or whether it was the fortably within range of CERN's LHC Polytechnique and Halina models used to interpret the data proton-proton collider. Abramowicz of Tel Aviv both drew which were at variance. His attention to the Pomeron, a math­ conclusion was that it is the models, ematical entity invoked some thirty and that we need to know more A fine thread of glue years ago to describe elastic scatter­ about the gluon distribution inside the ing phenomena, and once again in proton before we can reliably Monday morning's plenary session the spotlight. If the Pomeron has a interpret phenomena such as CDF's was held together by glue. CERN's high gluon content, it could help to jets. What at first appeared to be a Rolf Landua presented the work of explain effects seen at the HERA crack in the Standard Model turns out the "spectroscopy detectives" hunting electron-proton collider in Hamburg. to be just a lack of information down exotic particles. The existence HERA also reveals the structure needed to interpret the data. of a particle made entirely from function of the proton at low momen­ The thread of glue reached its end gluons, a glueball, said Landua, is tum fraction. The structure function with Warsaw's Jan Nassalski who now established, but it is not yet clear measures the momentum distribution pondered the question of "Why whether it is the f0(1720) found at of the proton's constituents. Accord­ nature has chosen such a complex

SLAC in the 1980s, or the f0(1500) ing to George Sterman of the State way to say one half." He was revealed by the Crystal Barrel University of New York, a rise was considering the spin of the proton, a experiment at CERN's LEAR not unexpected by quark-gluon spin-half particle whose spin was antiproton ring last year. Further theory, but more work is needed to once thought to be due to the quarks investigations are needed. The real understand the observed effect fully. inside. Now we know that the story glueball should also be found in J/psi Further Pomeron studies will also is not so simple, the spin comes decays, but it should not appear in "provide important input for the next partly from intrinsic angular two-photon physics since gluons generation of colliders", according to momentum, partly from the quarks,

4 CERN Courier, October 1996 Warsaw conference

The latest Standard Model results show that the most likely place to find the Higgs particle, responsible for electroweak symmetry breaking, is at 150 GeV.

but mostly, it appears, from gluons. Preliminary from 1 to 133 GeV and since a HERA's Hermes experiment, and s varies with energy, they are all perhaps the proposed COMPASS extrapolated to the Z-mass (91 GeV) spectrometer at CERN, will soon for comparison. Measurements from measure the gluon contribution deep inelastic scattering which used directly, by studying J/psi production to be low, and values from electro- in lepton-proton scattering. weak interactions, which used to be high, are now coming into line, giving New Physics a new global average of 0.118±0.003 consistent with theoretical calcu­ lations presented by Southampton's Kenneth Lane of Boston, embold­ Jonathan Flynn. ened by the new R measurements b Jeff Richman of the University of from LEP, provided a refreshing and California at Santa Barbara entertaining alternative to super- discussed heavy quark decays. symmetry, for which, he says, there Nearly all measurements are in good is not one scrap of evidence. Quot­ agreement with Heavy Quark ing Emily Dickinson "Faith is a fine Effective Theory which makes things invention when gentlemen can see, for the time being at least, the Stand­ easier to calculate by assuming that but microscopes are prudent in an ard Model can account for them all. heavy quarks are extremely heavy. emergency", Lane's clarion call was Reinhard Stock of Frankfurt sum­ The exception is the lifetime of the A look for evidence of alternative marized the results of the recent B baryon, which appears to be theories too. Graham Ross of Quark Matter conference, held in significantly lower than expected. Oxford, on the other hand, spoke for Heidelberg (July, page 1), and said Guido Martinelli of Rome threw some the majority when he urged that the "Lead beam SPS programme light on this in his discussion of experiments to go out and find is on the verge of a breakthrough." theoretical aspects of heavy flavour supersymmetry. Time will tell who, if He looked forward to the continuing physics. In reality, he said, the quark either, turns out to be correct! programme at the SPS, and the masses are not all large, and much Peter Maettig of Dortmund in his upcoming programmes at Brook- effort is being made to understand talk on new particle searches chose haven's RHIC collider and the LHC the so-called power corrections not to take up Kenneth Lane's call, for this breakthrough to be realized. which account for this. According to but to concentrate instead on Higgs At the more speculative level, Martinelli, the AB discrepancy and supersymmetry. Last year, CERN's Sergio Ferrara summarized between experiment and theory when LEP took its first step up in recent developments in superstring arises from just such a power energy, there was excitement in the theory where much progress is being correction. Aleph camp when a number of made to demonstrate the equiva­ curious events were detected. These lence of different candidate theories. each had four jets of particles with a Neutrinos and Cosmology combined mass around 105 GeV (January, page 1). At the time, Aleph Strong Coupling Constant and Heavy Tokyo's Yoichiro Suzuki summed claimed that although these events Flavours up the neutrino sector concentrating could be explained by the Standard on experiments which could show Model, they could also be new Michael Schmelling from the Max evidence for oscillations, neutrinos physics. But now with data from the Planck Institute in Heidelberg pointed changing from one type to another. other LEP experiments analysed, out that as, the strong interaction All of the five solar neutrino and new data from the 1996 LEP run, coupling constant, is the least well experiments detect fewer solar it looks like these are just Standard known of all Standard Model coupling neutrinos than the standard solar Model events after all. On the super- constants, but measurements are model expects. The new super symmetry front, candidate events beginning to converge. Measure­ Kamiokande detector, some 30 times exist at both Fermilab and LEP2, but ments are made at energies ranging larger (by mass) than its predecessor

CERN Courier, October 1996 5 Warsaw conference

Andrzej Wroblewski and Yoshio Yamaguchi share a joke between sessions.

10, and could have profound implica­ tions for the Universe. If the lower result is correct, then our current understanding of big bang nucleosynthesis could be in trouble. But it is too early to say which measurement is right. The analysis involves observing spectra from quasars seen through clouds of space dust, and the interpretation could be influenced by the presence of other material in the way. started taking data in April, and so far three: the dark side, the monster seems to see the same effect (July, side, and the opposite side of the page 22). In atmospheric neutrinos Universe. The dark side is character­ Future Detectors and Accelerators originating from cosmic rays, the ratio ised by the search for dark matter. of muon to electron type neutrinos is WIMPS, MACHOS, or a combination Enzo larocci of Frascati gave a not what is expected. Both these of both? WIMP stands for Weakly comprehensive overview of the phenomena could be explained if Interacting Massive Particle, perhaps advances which have been made in neutrinos have a mass, which would the anticipated supersymmetric the field of detectors from innovative allow them to oscillate. particles, but so far there's noevi- upgrades being prepared for the The Los Alamos Liquid Scintillator dence that they exist. MACHOs, Tevatron's detectors, to completely Neutrino Detector experiment, LSND, MAssive Compact Halo Objects, on new devices at Stanford and CERN. still claims to see evidence for the other hand, do seem to exist. Smaller, faster, radiation-harder was oscillations, finding candidate Two candidates have been found by the message delegates took away electron-neutrino events in a muon- gravitational lensing. The monster with them, almost paraphrasing the neutrino beam. But a similar side of the Universe is manifest on motto of the Olympic games, taking experiment, the KArlsruhe Rutherford Earth in the form of high energy place in Atlanta at the same time as interMediate Energy Neutrino cosmic rays which come from active the conference. Compact, fast and experiment, KARMEN, at the galactic nuclei. Could these be Black radiation hard detectors are needed Rutherford Appleton Laboratory in holes with a mass between one and to handle the LHC's unprecedented Britain, has so far not seen any a hundred million times that of the 800 MHz proton-proton collision rate. evidence for this effect. The sun? The opposite side of the In his talk on future accelerators, controversy will probably continue Universe could only be antimatter. Brookhaven's Robert Palmer, until long baseline experiments, such Are there antistars and antigalaxies concentrated on the speculative area as that which will send a neutrino out there? The AntiMatter Spectro­ of muon colliders. The idea for such beam from the Japanese KEK meter, AMS, will start to look when it machines dates back to the 1960s, laboratory to super Kamiokande 250 first flies aboard the space shuttle in but serious work only began this km away, and the NuMI project at 1998, and then on the space station decade, when it became clear that Fermilab (September, page 20) start from 2001 (November 1995, page 8). LEP was likely to be the last big to take data. The theory of neutrino The terrestrial antimatter highlight circular electron-positron collider. masses was presented by Alexei was the detection of antihydrogen at Muons seemed to present an Smirnov of the International Centre CERN in 1995 (March 1996, page 1) attractive alternative, but the main for in Trieste who paving the way for new experiments problem is that they don't live very looks forward to new results which to study spectral and gravitational long, and would average just 1000 will put the "huge edifice" of theory on effects. orbits before decaying. By more solid foundations. Robert Scherrer of Ohio State comparison, LEP's beams complete Saclay's Michel Spiro summed up concentrated on two recent measure­ over 11000 orbits a second, and are the emerging field of particle astro­ ments of the abundance of primordial stored in the machine for several physics, dividing his presentation into deuterium which differ by a factor of hours. A muon collider would have

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Metallschlauch-Fabrik Pforzheim Telefax ++49-7231/581-825 Warsaw conference

For the plenary sessions, the conference moved to the Palace of Culture and Science, a highly visible reminder of Poland's recent history.

collider show a general good agree­ Euroconference QCD ment with QCD predictions, and give estimates of some non-perturbative power corrections and improved nother snapshot of measurements of a . A contemporary particle physics, s The SMC Spin Muon Collaboration slightly more technical, came from at CERN has new results on the the 4th high energy physics Quantum polarized (spin-dependent) quark Chromodynamics meeting in structure of the'proton and deuteron, Montpellier, France. where the total spin does not reflect (QCD), the component quark spins. the field theory of quarks and gluons, Theoretical talks emphasized that has a traditional summer venue in this "spin crisis" is valid not only for Montpellier, organized by Stephan the proton, but is a universal QCD Narison. QCD 96 was the first of the property and should occur for any new Montpellier Euroconference target. Series in QCD sponsored by the The continued exploration by HERA European commission in Brussels. and by CERN's NMC muon Traditionally involving equal num­ collaboration of the low momentum bers of experimental and theoretical transfer (Q2) and momentum fraction talks and participants, the meeting (x) regions gives new impetus to also gives an opportunity for young perturbative QCD in these low- to have a very thick beam pipe to to contribute at an interna­ energy regimes. absorb radiation from decaying tional level, together with more For heavy quarks and leptons, muons, and the detectors would lose familiar names. It is thus a compro­ experimental results on production a 20° cone to shielding around the mise between a large scale interna­ and decays of B (containing the fifth beam for the same reason. The tional high energy physics confer­ 'beauty' quark) and D (containing the great advantage of muon colliders is ence and a small specialized fourth 'charm' quark) particles came their small size and cost. On the meeting. from the CLEO detector at Cornell's down side, since the ideas are all The programme covered various CESR electron-positron collider and new, there's a chance that they might QCD approaches, including from SLD and HERA. The sixth ('top') not work. perturbative series expansions - quark production and decays increasingly limited when the cou­ presented by the CDF collaboration To close the conference, Gabriele pling becomes strong - and alterna­ at Fermilab's Tevatron collider show Veneziano praised the "Joint effort" tive non-perturbative approaches. a good agreement with QCD being made by both experimentalists The first results from experiments at predictions and yield an improved and theorists "to understand not only CERN's LEP electron-positron measurement of the top quark mass. accelerator data, but also gravity, collider operating at higher energies A review of different determinations astrophysics, and cosmology." (130-150 GeV) on, for example, the of the QCD coupling showed how it

The next Rochester conference will quark-gluon coupling (ccs) are limited varies as the inverse of the logarithm be held in 1998 at the University of due the still low statistics available. of the energy, as predicted by QCD, British Columbia, Vancouver, Probing the collisions of quarks and from around the tau lepton mass of Canada. Next year's major confer­ gluons deep inside nucleons, data 1.8 GeV up to the LEP energy of 150 ence, the 1997 Lepton-Photon from quark and gluon jet production GeV, and the increasing range of Symposium will be in Hamburg, and event shape from LEP and from processes from which it can be Germany, and the 1999 Lepton- Stanford's SLD linear electron- extracted. Photon Symposium will be at positron collider, from Fermilab's The Crystal Barrel and Obelix Stanford, California. Tevatron (proton-antiproton collider groups at CERN's LEAR low energy and fixed target studies) and from antiproton ring have consolidated the DESY's HERA electron-proton by James Gillies evidence for 'gluonia' - fundamental

8 CERN Courier, October 1996