Quark Matter discussions - H. Gutbrod of the CERN WA80 experiment (left) with E. Fein berg of Moscow.

(Photos M. Jacob)

synthesis in the early Universe or the cooling of neutron stars. New developments in the pipe­ line are the proposed source of lead ions at CERN, and Brookhav- en's idea for the RHIC Relativistic Heavy Ion Collider to provide beams of 100 GeV per nucleon. Organized by G. Baym (Urbana), P. Braun-Muniziger (Stony Brook) and S. Nagamiya (Columbia, Chair­ man), Quark Matter 88 brought to­ gether over 250 participants, equally split between particle phy­ sics and nuclear physics. The next meeting in the series will be held in France in 1990.

From Maurice Jacob

the suppression of J/psi produc­ ratio of about 20 per cent) first tion seen by the NA38 experiment hinted by the 1987 results on very BROOKHAVEN at CERN. firm ground. At CERN, NA35 re­ At the Quark Matter 1988 meet­ peated a high yield of lambdas, 2.5 Glueballs, hybrids ing, held recently in Lenox, Massa­ times more than expected and in­ and exotics chusetts, the input from the sul- creasing with secondary multiplici­ phur-32 run at CERN consolidated ty. WA85 (using the Omega spec­ the results and conclusions drawn trometer at CERN) has looked at A workshop at Brookhaven from from the earlier oxygen run. The the production of lambdas and the August 29 to September 1 looked reasons for apparent J/psi sup­ corresponding antiparticles, finding at the current status of hadron pression were closely examined, an antiparticle/particle ratio twice spectroscopy beyond the realm of and while the quark-gluon plasma that of antiproton/proton formation states conventionally built up from hypothesis withstood all exper­ in proton-proton collisions at the quarks and discussed future exper­ imental tests presently possible, same energy. imental effort to explore such exot­ other scenarios, based on more Again, while not proving conclu­ ic states. conventional physics, presented sively that quark-gluon plasma is In an introductory talk on the valid viewpoints. Whatever its being produced, these strangeness current status of the quark model, cause, the clear experimental effect enhancements call for a system of N. Isgur of Toronto emphasized implies a system of high energy high density and appreciable life­ that this is now a mature picture, density (a few GeV per cubic fermi) time. successfully describing almost all and an appreciable lifetime (enough Seldom has particle physics pro­ the gross features of the observed for light to travel a few fermis). duced such interesting results from hadron spectrum. A flux-tube mod­ Main new result was evidence such short experimental runs. En­ el, with quarks bound inside ha- for an anomalously high production thusiasm to continue these studies drons by 'colour' flux and the of strange particles - another on the boundary between particle gluonic degrees of freedom natural­ possible quark-gluon plasma signal. physics and nuclear physics runs ly realized by its excitations, leads With a good set of results on high. As well as probing fundamen­ to specific predictions for hybrid charged kaon production, E802 tal questions in quark field theory, states. from Brookhaven puts the strange­ the issues are also of great interest In quark field theory, the carriers ness enhancement (a kaon to pion to astrophysicists studying nuclear of the inter-quark force - the gluons

CERN Courier, December 1988 25 Dave Hitlin of Caltech (left) discusses exotic hadron spectroscopy with Suh-Urk Chung of Brookhaven.

its copious production in J/psi ra­ diative decays. Since it is also ob­ served in conventional hadronic production channels at Brookhaven and at the Japanese KEK Laborato­ ry, in addition to proton-antiproton annihilation channels at CERN, it is likely to be quarks mixed with a glueball, or perhaps a hybrid quark/gluon state. Brookhaven data from a high statistics experi­ ment for hadroproduction of E(1420)/iota(1440) show evidence of complex structure in the 1400- 1450 region. States may exist with slightly different masses and decay patterns. The hybrid workshop focused on the study of mesons with quantum number assignments defying clas­ sification as conventional quark states, such as the M( 1406) and — are themselves sources of the non-standard S states (January/Fe­ the U(3100), and those with de­ force, so that gluons, as well as bruary 1987 issue, page 16) at cays that do not correspond to quarks, should be able to stick to­ 991 and 988 MeV. Four-quark simple quark-pair creation, such as gether to form particles. S. Sharpe 'molecules' such as the S(988) the C(1480), supplemented by oth­ of Stanford reviewed progress in may show up only in neutral kaon er exotic states, such as the lattice gauge theory. Though relia­ pair channels, while zero-spin, po­ E(1420), produced by more com­ ble predictions are difficult for the sitive parity quark-antiquark bound plex mechanisms. The longest dis­ masses of such 'glueballs', certain states would be heavier, in the cussions were on the exotic mass ratios are better determined. range of 1.3 to 1.5 GeV. Then the M(1406) following reports by the At a special workshop, there S(991) may well be the lightest GAMS group (May issue, page 21). were many speculations about glueball. Despite the lack of conclusive which candidate would claim the F. Binon of Brussels discussed evidence, all agreed that the results prize for being the first definitive another candidate, the G(1590) so far underline the importance of glueball, with enlightening ex­ seen in eta decay modes by the neutral particle detection in unrav­ changes, sometimes heated, be­ GAMS group. elling the hadron spectra. More ex­ tween the competing camps. The three spin-two positive pari­ periments in this area are needed, This glueball workshop covered ty phi-phi states observed in nega- and several proposed studies at hadronic production of glueball tive-pion/proton interactions are KEK and Brookhaven to confirm the candidates by both single- and considered by many to be glueball GAMS results were described. double-particle exchanges, together candidates, as is the theta(1720) In a special joint glueball and hy­ with the traditional glue-rich J/psi seen in J/psi radiative decays. At brid session covering two-photon radiative decays from electron-po­ the meeting, there was a dis­ physics, recent experimental data sitron production. The workshop cussion of the theta spin-parity as­ were confronted with the predic­ underlined the importance of all signment. Though spin two is still tions of some favourite four-quark three production processes and favoured, a significant spin zero models by N. Achasov and by K. F. their inter-relationship for glueball component is not yet ruled out. Liu. searches. The iota(1440) was long claimed I. Shipsey of Syracuse covered M. Pennington (Brookhaven/Dur- to be a prime spin zero, negative the status and future of the physics ham) presented evidence for light parity glueball candidate because of of B mesons (containing the heavy

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CERN Courier, December 1988 27 Theory and experiment at the College de France's 'higher twist' workshop. Standing, theorist Marcel Froissart of the host institu­ tion, one of the organizer^ of the meeting. Seated, Terry Sloan of the European Muon Collaboration experiment.

'beauty' quark) using the CLEO de­ different possible quark/gluon in­ tector at Cornell's CESR electron- teractions. In addition to the 'lead­ positron ring, where 'charmless' B ing term' frequently used as the ba­ decays are not seen, in contrast to sis for QCD calculations, additional last year's results from the ARGUS contributions - so-called 'higher experiment at the German DESY twists' — are modulated by powers Laboratory (October issue, page 3). of kinematical factors. An illuminat­ The B physics potential of the ing international workshop to dis­ Relativistic Heavy Ion Collider cuss higher twist QCD was held at (RHIC) proposed at Brookhaven the College de France, Paris, from was discussed by W. Morse, high­ 21-23 September. lighting the crucial role fresh in­ Evidence for higher twist effects sights would play in our under­ is accumulating from many quart­ standing of weak decays. ers. Impressive new data from an The need for a 'B-factory' was experiment by a Chicago/Iowa/ universally accepted but the type of Princeton collaboration at Fermilab machine needed was (and will be) a were presented by Kirk McDonald topic of continuing debate. of Princeton. This experiment The detectors and facilities measures the quark structure workshop explored the next gener­ (structure function) of the pion un­ ation of these devices and how der conditions where a participat­ they could make an impact on the ing quark carries a high proportion unanswered questions in hadron of the momentum. Characteristic spectroscopy. It was emphasized evidence for higher twist is seen, that a continued worldwide effort showing that the incident pion in­ was necessary. Overall, the meet­ teracts coherently with a target ing highlighted hadron spectrosco­ quark. Ed Berger of Argonne re­ py as a crucial testing ground for viewed higher twist in lepton pair current particle physics ideas, and production and forward jet sup­ looked forward to a detailed con­ pression. frontation of lattice calculations The theory of direct production with experiments. The participants was covered by Reinhard Ruckl and left with a feeling that real progress Maurice Benayoun for heavy and had been made in the past few light quarkonia (bound states of a year, and a resolve to continue to quark and an antiquark) respect­ explore unconventional quark ively. Particularly interesting was states - a subject at the very heart the development of the relativistic of matter. treatment of the light quarkonia to include mesons where the consti­ From S.-U. Chung tuent quarks have orbital angular pression through a coherent inter­ momentum, the result of a recent action of the incident meson - has study by Benayoun and Marcel been seen by Fermilab experiment Froissart. E609. Paulo Nason of ETH Zurich WORKSHOP Evidence for the direct lepto- explained why production of heavy Let's twist again... and hadroproduction of mesons quarks unpaired with their corre­ was reported from CERN experi­ sponding antiquarks is well under­ ments WA59 and WA77 respect­ stood qualitatively. There are still In the quantum chromodynamics ively. The latter is analysing new problems with the absolute predic­ (QCD) candidate theory of inter- data to look at energy dependence. tions for J/psi production, with quark forces, calculations involve In addition, the related time-rev­ further input to come from the Eu­ summing the effects from many ersed process - forward jet sup­ ropean Muon Collaboration.

28 CERN Courier, December 1988