Standard Model festival

The Hamburg Lepîon-Photon Symposium also marked the tenth anniversary of the discovery at Fermilab of the upsilon particle (beauty 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 '' of modern , with the (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 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 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- 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) . 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 (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'. Neutrino parameters inferred from the supernova counts agree broadly with laboratory measure­ ments, but Schramm pointed out that now these detectors have shown what they can do, it should be possible to pick up signals from the additional supernovas whose light is blotted out by dust. M. Turner, another Chicagoite, reviewed the 'renaissance' in cos­ mology through advances in parti­ cle physics. 'Heavenly laboratories' can supplement what we know from terrestrial experiments. One that while the Standard Model soon the Kamiokande underground of the current cosmological puzzles reigned supreme, many of its para­ detector in Japan could supply an is the 'dark matter' of the universe meters had still to be measured. independent measurement. Exper­ One continual enigma is the sub­ iments measuring the mass of the W. Schmidt-Parzefall of DESY's ARGUS collaboration - charmless beauty decay. tle asymmetry (CP violation) in the electron neutrino still give a spread decays of the neutral kaons. Italo of values, but with the Zurich Mannelli of Pisa emphasized how group saying the neutrino is lighter little has been learned in the 23 than 18 electronvolts and the ITEP years since the effect was first Moscow team reporting a mass observed. However precision ex­ greater than 17 electronvolts, Eich­ periments continue to probe this ler said there was not necessarily area. Mannelli highlighted the NA31 any disagreement! experiment at CERN which has Neutrino physics took a big step studied millions of neutral kaon forward earlier this year with the decays. Results from this and other observation of particles from a ongoing studies could help under­ supernova explosion (see May stand this mystery. issue, pagel). At Hamburg, Whatever else is happening, M. Koshiba (Kamiokande, Japan), neutrino physics can usually be 0. Saavedra (Mont-Blanc, Europe) relied on to be controversial. How­ and D. Casper (1MB, USA) re­ ever Hamburg neutrino rapporteur viewed the experimental evidence. R. Eichler of ETH Zurich admitted The implications were taken up that even the standard model of by Dave Schramm of Chicago. The neutrinos looked to be in 'good big push for constructing these shape'. big underground detectors had The longstanding disagreement followed the prediction about ten between theoretical predictions years ago by the then-emerging for the rate of neutrino emission theories of the 'grand unification' by the sun and the observed level of the strong nuclear and electro­ seen in Ray Davis' underground weak forces of an unstable proton. detector is still there, but very Although odd events have turned

CERN Courier, October 1987 5 - electromagnetically inert stuff projects for a big hadron circular ma' of opting for existing technol­ which nevertheless makes up the collider and an electron-positron ogy, or of embarking on schemes gravitational bulk of the universe. linear collider, both to probe needing a substantial development Turner advocated that the current around the magic 1 TeV collision effort to get them off the ground. 'passionate theoretical predictions' energy at the electron/constituent should be counterbalanced by at­ quark level, pointing out the 'dilem- Report by Gordon Fraser tempts at measurement. Another tenth anniversary at \\\ Hamburg was that of ICFA - the International Commitee for Future Accelerators. Chairman Yoshio Yamaguchi reviewed ICFA's achievements and plans. A. Polykanov of Moscow's Landau Institute had been sched­ uled to speak on the final day of the meeting, but a last-minute in­ disposition led to an even later- minute substitution by Sheldon Glashow, who looked at the impli­ cations of a not so standard model for future experiments, particularly at the LEP machine at CERN. Hard electromagnetic processes (F. Richard, Orsay) are providing valuable physics input, while high energy neutrino beams (J. Panman, CERN) are giving broadly consistent results, with the mysterious excess of like-sign muons beginning to disappear. High energy photopro­ duction (M. Witherell, Santa Bar­ bara) provides good information on particle properties (charm life­ times). Summarizing the very active field of photon-photon interactions, J.-E. Olsson of DESY found himself having to contend with an 'appre­ ciable percentage of all papers contributed to the conference!'. A session on new projects sum­ marized the status of machines just around the corner - the Stan­ ford Linear Collider (Burt Richter), CERN's LEP electron-positron col­ lider (Albert Hofmann) and DESY's HERA electron-proton collider (Gus Voss). But it was left to Carlo Rubbia Conference dinner in Hamburg's Fischauktionshalle. to look further into the future, ex­ amining 'highly complementary' (DESY photos by Jurgen Schmidt)

CERN Courier, October 1987 7