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Standard Model Festival Standard Model festival The Hamburg Lepîon-Photon Symposium also marked the tenth anniversary of the discovery at Fermilab of the upsilon particle (beauty quark and antiquark bound together). At a Fermilab celebration of the discovery earlier this year were (left to right) Alvin Tollestrup, Sandy Anderson (with balloon), Hwa Yoh, Leon Lederman, Janine Tollestrup, Drummond Rennie, Martyl Langsdorf and Vivian Bull. The 'Standard Model' of modern particle physics, with the quantum chromodynamics (QCD) theory of inter-quark forces superimposed on the unified electroweak picture, is still unchallenged, but it is not the end of physics. This was the message at the big International Symposium on Lepton and Photon Interactions at High Energies, held in Hamburg from 27-31 July. The conference is a celebration of the Standard Model', admitted Graham Ross of Oxford, given the task of looking beyond. He pointed out a few interesting clouds on the horizon, and echoed the in­ creasing belief that experiments at higher collision energies (1000 GeV for constituent quarks inside nucléons or for electrons) would probe deep inside the Standard Model and reveal some­ thing new. Carlo Rubbia of CERN flew in at the end of the meeting with some suggestions for future machines to explore these far horizons. 'However our preoccupation with high energy should not exclude other interesting topics,' he warned, mentioning solar neutrino dronic events per day, and are plained single muons accompany­ studies, particle mixing, CP viola­ providing interesting new informa­ ing produced hadrons, reported tion, the search for proton decay tion to take over where the elec­ by some studies at the PETRA ring and supernova detection ('We tron-positron machines at Stanford at DESY (see September issue, should be better prepared next (US) and DESY (Hamburg) left off. page 37), but TOPAZ and AMY time!'). With other machines on its further round the ring had nothing The conference business began heels, TRISTAN also has to push yet to report on this subject. How­ with Satoshi Ozaki of the Japanese its collision energy. While runs this ever AMY does see a slight excess KEK Laboratory describing the new year should see 27 or 28 GeV per of isolated energetic photons, but TRISTAN electron-positron collider, beam, this could be increased to it is too early to draw conclusions. currently providing the world's 30 or even 33 GeV next year after Although starting later than the highest electron-positron collision the installation of superconducting other big experiments, TOPAZ has energies for physics. Collision rates accelerating cavities. now logged a comparable amount are good, with the luminosity al­ F. Takasaki of KEK covered the of data. most at the 1031 cm"2 s~1 design physics results from the TRISTAN At another newly commissioned level. 'With other machines follow­ experiments, emerging at an im­ machine - the Fermilab Tevatron ing close behind, we also had to pressive rate. As yet, no new proton-antiproton collider - Roy push the physics programme,' thresholds indicate the arrival of Schwitters of the big CDF detector Ozaki remarked. TRISTAN experi­ new quarks. The VENUS detector covered progress so far. The ma­ ments have logged about 30 ha- has seen some signs of the unex­ chine has performed excellently, CERN Courier, October 1987 1 Carlo Rubbia - future machines. been pounced on by adventurous theorists. CERN collider results so far sug­ gest that the long-awaited sixth ('top') quark is heavier than about 45 GeV, while the number of pos­ sible neutrino types is now less than about five, leaving little room beyond the three known species. The machine is now embarking on a second phase of operation, with the antiproton supply boosted with the new ACOL antiproton collector. In his conclusion, Rubbia under­ lined the need for a (spontaneous symmetry breaking) mechanism to explain the very different ranges of the electromagnetic and weak forces in the electroweak picture. The currently advocated 'Higgs' solution is 'clumsy', he maintained, and went on to point out that whatever the mechanism is, there are good hopes that proposed future proton colliders will find evi­ dence for it. Elsewhere in the electroweak sector, things are in good shape. However A. Sirlin of New York stressed the need for highly accu­ rate calculations (with full radiative corrections) to pin down any tell­ tale discrepancies due to new phy­ sics. Less clear-cut is the quark-gluon side of the Standard Model, where James Stirling of Durham picked his way carefully through the 'mi­ with collision luminosities already a similar way at lower energy at nefield' of QCD calculations. Be­ not far from design values (over CERN in 1983). cause series solutions are not ne­ 1029 cm"2 s~1 compared with 1030) The physics of the W and Z par­ cessarily convergent, QCD can at collision energies of 1.8 TeV ticles garnered from experiments only be handled confidently if the (1800 GeV) - the highest in the at CERN's proton-antiproton collid­ kinematics are right. However ex­ world. er was described by Peter Jenni. periments using different physics Schwitters hoped that summary The first phase of proton-antipro­ conditions report comparable re­ tapes to extract physics data ton physics has not threatened the sults for QCD parameters, and should be available later this year. Standard Model', he declared, predictions are becoming more The detector has seen candidate pointing out nevertheless that the precise. Stirling highlighted the events for the production of the UA1 experiment has seen a couple spectra of hadron 'jets' seen in W and Z carrier particles of the of unusual W decays at high trans­ proton-antiproton annihilation, weak nuclear force (discovered in verse momentum. These have showing how calculations agree 2 CERN Courier, October 1987 The VENUS detector at the TRISTAN electron-positron collider at the Japanese KEK Laboratory. VENUS, and its TOPAZ and AMY counterparts elsewhere in the ring, produced data from the initial TRISTAN runs with impressive speed for the summer conference season. (about a picosecond). Annihilations giving a photon plus 'nothing' (unobserved particles) give a han­ dle on neutrino production, show­ ing that the number of neutrino types has to be less than about five, in accord with what is seen in proton-antiproton annihilation. The Lepton-Photon Symposium ten years previously had also been held in Hamburg, when the big news had been the sighting of the first bound state - the upsilon - of the beauty quark and antiquark. Juliet Lee-Franzini of Stony Brook showed how upsilon spectroscopy has developed over the ensuing decade, providing a valuable addi­ tional means of probing inter-quark forces. D. Hitlin of Caltech reviewed the weak decays of charmed particles with the data over an impressive in proton structure measurements and heavy (tau) leptons. The earlier range of kinematics. To extend could improve the agreement be­ report of an unorthodox decay of this range, the first hard data from tween the predicted and observed the tau (see April issue, page 10) the CDF detector at the Fermilab levels of W and Z production with has been overturned in a 'flood' Tevatron collider are eagerly energy in proton-antiproton anni­ of null results, but the total map awaited. While QCD calculations hilations. According to Voss, it is of tau decays still has to be are becoming more reliable, they not always easy to reconcile charted accurately. are laborious, with effort measured measurements from different ex­ Hitlin's talk carefully avoided the In terms of man-years,' according perimental conditions. However physics of the B mesons (carrying to Stirling. the ratio of longitudinal to trans­ the beauty quark) as this had been Another sector full of implica­ verse production rates from exper­ reserved for W. Schmidt-Parzefall tions for QCD was particle produc­ iments at Stanford and CERN of DESY, who was able to report tion using electron and muon agrees with QCD predictions. the first observation, in the ARGUS beams, covered by Rudiger Voss Production of hadron 'jets' in detector at the DORIS electron- of Munich. These experiments also hard interactions is now a powerful positron ring at DESY, of the de­ see the subtle changes in the quark way of probing quark behaviour. cays of the mesons without pro­ structure of nucléons (structure W. Hofmann of Berkeley described ducing charm (see September is­ functions) due to nuclear environ­ attempts to understand the way sue, page 4). In general, the pat­ ment. The intense theoretical spe­ quarks and gluons (which do not tern of B meson decays looks tidier culation of recent years seems to appear as free particles) produce than a year ago, when there was be waning as the experimental pic­ these characteristic narrow show­ talk of a 'charm deficit'. ture firms up. Nevertheless 'an ers of particles. The implications of these weak ultimate theory is urgently needed,' As well as providing input for decays was taken up by M. Shif- concluded Voss. QCD, electron-positron annihilation man of Moscow (ITEP), who admit­ Away from nuclear effects, the at high energy (covered by Sau-Lan ted to being initially 'surprised' by quark structure of the proton has Wu of Wisconsin) shows the deli­ the amount of charmless B decay to be known accurately to provide cate interference between weak seen by ARGUS. However this input for calculations, and Voss and electromagnetic effects and surprise had evaporated on closer remarked how the slight difference gives the lifetime of the B meson inspection. Shifman pointed out CERN Courier, October 1987 3 Electron-positron collider notables at Hamburg - Satoshi Ozaki (KEK, Japan, left) and Burton Richter (Stanford). up, proton decay has yet to be proved. Schramm quoted Luis Al­ varez - 'the neutrino detection of the 1987a supernova is a great success for grand unified theories'.
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