Singapore's Double Festival
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Singapore's double festival The 25th International Conference on High Energy Physics in Singapore from 2-8 Au• gust was opened by Singapore Trade and Industry Minister Lee Hsien Loong (left), seen here with K. K. Phua, Chairman of the Conference Organizing Committee. Coinciding with celebrations for the nation's 25th anniversary, the 25th International Conference on High Energy Physics, held in Singapore from 2-8 August, was itself a dou• ble festival, with the Standard Model of contemporary physics and CERN's new LEP electron-posi• tron collider providing the twin themes. At the Stanford Lepton-Photon jamboree last summer, Stanford's SLC electron-positron linear collider just pipped LEP to the post for the first examples of Z particles - the electrically neutral carrier of the weak nuclear force - produced by electron-positron annihilation. One year down the line, Singa• pore rapporteur Friedrich Dydak, covering electron-positron Z phy• sics, was able to present an aval• anche of new data - some 500,000 Zs intercepted by LEP's four big experiments - Aleph, Del• phi, L3 and Opal. This solid block didn't. With little laboratory evi• durian - a large, unsightly tropical of new information reinforces the dence to show, he nevertheless fruit of dubious taste banned from Standard Model, the two-sided pic• played two strong cards; 'Dark Singapore hotels and the subway ture of particle physics with the Matter'- the realization that the Uni• because of its nauseating smell. electroweak unification of electro- verse must contain more than can With the four LEP experiments magnetism and the weak nuclear be seen directly - and the multipli• each providing separate contribu• force on one hand, and the field city of arbitrary parameters which tions, the Singapore parallel ses• theory (quantum chromodynamics plague the Standard Model itself. sions on electroweak Z physics, on - QCD) of quark-gluon interactions Alone, these two strong hints sug• heavy quark production, on jets responsible for the strong nuclear gest that there is a deeper physics and fragmentation and on particle force on the other. encased in the hard shell of the searches provided a fat chunk of Already looking impregnable at Standard Model. LEP material. For the plenaries, the the previous Rochester meeting in Another big question mark contributions from the four experi• Munich in 1988, when LEP was hangs over the Higgs mechanism, ments were distilled into the histor• still under construction, the Stan• the spontaneous symmetry-break• ic review by Dydak and a detailed dard Model now reigns supreme. ing which endows the electroweak review of jet physics and QCD by Given the task of updating the vacuum with special properties and CERN's Maurice Jacob. Standard Model at Singapore, rap• gives particles their mass. Vital to The road to LEP Z physics had porteur Cecilia Jarlskog of Stock• the smooth running of the picture, been well prepared by some 1500 holm enthused over the richness of the Higgs mechanism is neverthe• theoretical papers which examined this picture rather than despairing less unknown and unexplored. Un• the 'radiative corrections' the over the absence of new informa• daunted, Jarlskog awarded the numerous subtle mechanisms tion. Higgs sector a delicate tropical or• which contribute to electron-posi• Delegated to look beyond the chid for its attractiveness. Less ap• tron interactions at these energies. Standard Model, Moscow's Lev preciative was summary speaker The knowledge of the Z mass is Okun could have despaired, but J.D. Bjorken, awarding the Higgs a limited mainly by the remaining CERN Courier, September/October 1990 1 On the occasion of our 15TH ANNIVERSARY We take this opportunity to thank all our faithful European clientele for its continued support and patronage. We take great pleasure in annoucing our newest "baby" # available for you this coming winter "Vantage 300 TM The model 3968 rtVAX 300 Intelligent CAMAC Crate Controller Please contact us for further details Headquarters Europe-Marketing Germany 3, chemiKINETIn Taverney C SYSTEMGewerbestrassS e INTERNATIONA13 MozartstrassLe 21S A CH-1218 Geneva, Switzerland CH-4528 Zuchwill, Switzerland D-7800 Freiburg, W. Germany Phone: (22) 798 44 45 Phone: (65)25 29 25 Phone: (76)13 32 65 Fax: (22)798 05 25 Fax: (65) 25 5117 Fax: (76)12.32 46 rtVAX 300 is a Trade Mark of Digital Equipment Corp. Vantage 300 is a Trade Mark of Kinetic Systems Corp. 2 CERN Courier, September/October 1990 Nearly time to start. Friedrich Dydak of CERN (left), who opened the Singapore plen• ary sessions with a milestone talk on new results in electron-positron Z physics, checks his watch with session chairman J.-E. Augustin. neutral B mesons (containing the b quark) to extract a value for the mixing parameter in line with earlier determinations from the ARGUS experiment at DESY's DORIS elec• tron-positron ring and the UA1 ex• periment at CERN's proton-antipro- ton collider. These initial'measurements of B particle mixing had provided the first hints that the top quark could be heavier than expected. With the new limits from the LEP experi• ments, the heavy top quark be• comes a way of life, and the mixing measurements gain respectability. Aleph gets a lifetime for B parti• cles of 1.28 x 10 12 seconds, in line with the previous world aver• age of 1.13 x 1012. Studies of charm production are well under• way, while Opal compares different light quark (u and d) properties from a sample of photon produc• tion. The LEP data provides a fresh source of information on QCD ef• fects. The underlying QCD coupling 30 MeV (In 90 GeV) uncertainty ballparked with such confidence. strength is expected to 'run' - to in LEP's energy calibration. Two years ago this quantity was depend on energy - and Z While the shape of the Z reson• anyone's guess, (although initial measurements at LEP provide a ance is now well determined, and measurements of B particle mixing new benchmark. Awaiting a preci• the number of neutrino families had hinted that it might be high), sion analysis of LEP hadronic Z in• now fixed as 2.89 ± 0.10, Dydak while quantitative suggestions fol• formation, and with the individual emphasized that there is still room lowed from the initial precision interactions of constituent quarks for further improvement in preci• fixes on the Z mass at Stanford's and gluons themselves invisible, sion tests of the Standard Model. SLC linear collider and at LEP one QCD details have to be inferred by And the 1989/90 harvest of Zs is year ago. studying the production of jets - only a foretaste of things to come Additional progress is visible in well-defined emergent sprays of - the plan is to catch more than measurements of the coupling particles. Analysis of these jets three times as many Zs next year. strengths of the weak force. also shows the characteristic three- The wealth of LEP data is com• Where only recently the overlap gluon vertex of QCD, when a single pletely in line with all other Stan• from different experiments gave a gluon 'breaks up' into two. dard Model measurements, so that fuzzy picture, these couplings have Earlier, jet analysis was topologi• consistency arguments give a lever now been pinpointed by LEP. cal, with the shape of the jets be• on the unseen but long-awaited Most of LEP's Zs decay into ha- ing the main criterion, but this is sixth ('top') quark, which now ap• drons, and the experiments see now complemented by energy cor• pears to lie at 137 ± 40 GeV. about 20 per cent of these produc• relations between jets, while com• With little new physics to report, ing the fifth ('beauty' - b) quark, in parison of the production levels of it is nevertheless a sign of progress line with expectations. 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