Warsaw Conference of the 1996 Rochester Conference
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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 Physics has been a festival of the Standard Model, 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 supersymmetry, 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 anomaly 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 Gabriele Veneziano, 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 Fermilab'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 2 CERN Courier, October 1996 - HUNT ENGINEERING — are coming to Cern! See us 8th-llth October 1996 'Britain at Cern' • Modular Solutions for Parallel and Multi DSP Systems • Development tools and systems for TMS320C4X • Data Aquisition Sytems • High Speed Data Processing and Storage HUNT ENGINEERING Chestnut Court, Burton Row, Brent Knoll, Somerset TA9 4BP UK Phone (+44) 1278 760188 Fax (+44) 1278 760199 Email [email protected] High And Your partner for a full service: Low Voltage prepress - printing - binding - Power Supplies distribution High Stability + Low Ripple Many standard types ex stock certified according to DIN ISO 9001 lannoo LANNOO PRINTERS Kasteelstraat 97, B-8700 Tielt-Belgium Tel. 32 51 42 42 11 - Fax 32 51 40 70 70 F.u.G. Elektronik GmbH - Florianstr. 2 - D-83024 Rosenheim Tel...49(0)8031/2851-0 • Fax..49(0)8031 /81099 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.