Glasgow conference Pierre Darriulat of CERN gives the summary talk at this year's International Conference on High Energy Physics, held in Glasgow. (Photos University of Glasgow) he biennial 'Rochester' Interna­ T tional Conferences on High Energy Physics which tick the rhythm of high energy physics progress reflect the dominance of the 'Standard Model' - the picture of electroweak and quark/gluon interactions in a simple framework of six weakly- interacting particles (leptons) and six quarks. Despite its limited intellectual appeal, after a decade of intense probing the Standard Model still refuses to budge. This year's Rochester event, held in Glasgow from 20-27 July, followed the trend. But conformity is not a synonym for a physics vacuum. The advent of high precision data from big colliding beam experiments provides a treasure trove of detailed information on particle characteristics and decays, so that Standard Model physics becomes charted in finer and which has already definitely ruled out for the top quark but does not firmly finer detail. (A preliminary Glasgow the top quark being lighter than 131 establish its existence,' declared report appeared last month, page 1.) GeV. Jensen. However the map is far from com­ After careful elimination of back­ Seven CDF events have enough plete, and as Glasgow summarizer ground effects in the initial data kinematical information to calculate Pierre Darriulat of CERN concluded, sample, CDF found two spectacular the top quark mass, giving a value of there is a lot to do while waiting for events producing an electron and a 174 GeV ± 10%. the next round, which will begin in muon, but none with an electron or a DO reports one example of a muon- about ten years when CERN's LHC muon pair. It is almost impossible to electron pair, and six candidates proton-proton collider begins opera­ explain these spectacular electron- including jets. 'There is no significant tions. muon events by any other mechanism. excess over background,' said In searches where the top leaves its Grannis, adding that the interim DO fingerprint as a characteristic accom­ result is consistent with no top Top quark panying particle containing the fifth production. ('beauty' - b) quark and a confined Earlier in a parallel session, Keith A new feature of physics in 1994, 'jet' of accompanying hadrons ('the Ellis of Fermilab had compared the still firmly part of the Standard Model, nicest part of the analysis' according top production rates as calculated is first evidence from Fermilab's to Jensen), CDF sees six candidates from CDF and DO interim results Tevatron proton-antiproton collider of using the vertex detector to pick up with the theoretically expected value. the long-awaited sixth ('top') quark. the short track stubs left by decaying CDF overshoots and DO under­ First presented at Fermilab earlier B particles (containing a b-quark) and shoots, making it tempting to com­ this year (June, page 1), the data had another seven through the analysis bine the two small sets of data, but slightly matured at Glasgow. of weak decays producing a lepton. several speakers warned that this In the plenary sessions, Hans In total CDF sees 15 candidate top would be premature. Jensen presented the top quark events (really 12, as several exam­ If the top quark mass could be fixed evidence from the CDF experiment, ples are caught in two analysis nets), to within 3 GeV, the consistency net while Paul Grannis spoke for the compared with an expected back­ of the Standard Model could trawl a companion Tevatron DO experiment, ground of six. 'This gives evidence value for the mass of the long- 2 CERN Courier, October 1994 Glasgow conference Joel Feltesse of Saclay, spokesman for the H1 Ritchie Patterson of Cornell - weak and rare experiment at HERA - 'The structure of the decays. proton continues to be mysterious'. Electroweak physics Dorothee Schaile of CERN, cover­ ing precision electroweak tests, followed the top quark talks on the first day of the Glasgow plenaries. In a field dominated anyway by the weight of statistics from the four experiments at LEP, added precision now comes from improved luminosity measurements and a new calibration of LEP beam energy, potentially fixing the Z mass to within a few MeV. Not all these refinements have yet been incorporated in the ongoing analysis, and updated figures are continually emerging. While LEP's energy now takes account of tidal effects and other minutiae, a now predictable residual effect remains. LEP data provides more and more fixes on Standard Model parameters, awaited higgs particle at the root of with even once esoteric areas like Darriulat, echoing C.K. Jung of DO in the delicate electroweak symmetry tau physics and B production contrib­ the parallels, pointed to the particular breaking mechanism which makes uting. Tuned to the Z, LEP cannot yet example of the W mass, which does the Standard Model tick. get at the Z's electrically charged not favour the SLD result. The offset Far heavier than any other known companion, the W boson. A new between the SLD and 'other' results particle, the top quark could be trying precision fix on the W mass (80.23 drives the world average limit for the to tell us something. The possibility of GeV) comes from CDF and DO at the top quark mass from 171 to 178 GeV. new insights into quark dynamics Tevatron. By itself, the SLD results centres on a was underlined by Pierre Darriulat in A new but not unexpected top quark mass of 240 GeV. his summary, who eagerly looked electroweak effect involving the W forward to more Tevatron top data. comes from the HERA electron- (During the conference, the Tevatron proton collider, where the falloff in Third generation broke new luminosity records - neutrino production attains the September, page 42 - promising well energy region which reflects the W The top's companion quark in the for the future.) mass. heaviest quark duo is beauty (b). The Obviously the top evidence was A highly precise electroweak properties and spectroscopy of the B high on Darriulat's summary agenda. measurement is the left-right asym­ particles containing this quark have As well as congratulating CDF in metry in Z production by the SLD now developed into a minor research communicating these exciting new detector using polarized beams at industry. As well as the mass of data results, he underlined the close the SLC linear electron-positron from the CLEO detector at Cornell's agreement between the top quark collider at Stanford (SLAC - May, CESR electron-positron collider and mass emerging from the Tevatron page 11) and described by Mike Fero final results from the now complete data and the limits now emerging of SLAC in the early Glasgow parallel ARGUS study at DESY's DORIS from the world mass of Standard sessions. ring, summarizer Darriulat pointed to Model data, where the precision While not impossible, it is not easy many important contributions from results from CERN's LEP electron- to reconcile this precision result with LEP experiments, at CDF and at S proton collider play the major role. the majority of the electroweak data. using new microvertex detectors 4 CERN Courier, OcfMtt^94 Glasgow conference Physicist Hallstein Hogaasen of Oslo and his Michal Turala's Glasgow overview of new wife sailed to Glasgow from Norway in their detectors and experimental techniques boat 'Emotion', which during the Conference showed the impressive progress being made was moored on the River Clyde in front of the to meet new physics challenges. Conference Centre. Standard Model's lepton partner of the t- and b-quarks, is also in better shape this year. In previous years some apparent shortfalls in certain decay sectors had given mild con­ cern. ' Roger Forty of CERN showed how LEP experiments also see the actual oscillations between different neutral B states (rather than just broad evidence for mixing). Awaiting more B particles and the next generation of neutral kaon experiments, the CP violation scene features first results from the CPLEAR experiment at CERN's low energy antiproton ring. Proton structure The structure of the proton contin­ ues to be mysterious,' remarked Joel Feltesse of Saclay. As spokesman These precision detectors immedi­ for the H1 experiment at HERA, HERA data now probes deep inside ately around the beam collision point Feltesse was naturally proud to show the low x (momentum fraction) reveal the tiny track stubs left by the the new HERA results on the proton region, so that the increasing rich­ decaying b particles. structure when the struck quark ness of nucleon quark/gluon content In his talk on heavy quark physics, contains only a tiny fraction of the first seen last year is both continued Patrick Roudeau of Orsay showed parent proton momentum. and accelerated. This hints at a large how the B quark sector is now But first Feltesse preferred to look variation in gluon content for the emerging as another realm where the at results from CERN's NA51 muon proton. A flat gluon content can be Standard Model reigns supreme. pair experiment and from a compari­ ruled out under these conditions. However there is still plenty of work son of positive- and negatively- Another continuing feature of the to be done in pinning down B life­ charged W production by CDF. HERA data is the 'rapidity gaps', the times and the details of many decay These show that the three valence kinematical bunching which suggests channels. quarks of the proton are accompa­ that sometimes the incoming electron While last year the sighting of a rare nied by a collection of 'sea' quarks probes the proton 'diffractively' - ('penguin') neutral B decay into a K* which is not flavour symmetric (more analogous to what happens in elastic and a photon by CLEO was a talking down- than up-quarks).