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Home , Emanuele Quercigh, Matter, Quark

The WA85 heavy ion beam experiment at CERN has found increased yields of antihyperons, difficult to produce hadronically, compared to what is seen in other reactions.

to focus about half of the emerging -polarized hydrogen ; the resulting polarized of about 1013 cm-2 should give a luminosity of 1032 cm2 s1 when crossing the 400 GeV UNK-1 beam.

Quark 93

In his welcome address to the 10th International Conference on Ultra- Relativistic Nucleus-Nucleus Colli­ sions ( Matter '93), held in Borlange, Sweden, from 20-24 June, Hans-Ake Gustafsson was puzzled why this year's conference was billed of the hot and dense matter at or stage of the collision as an ideal as the tenth in the series. near equilibrium, and the interface of and . As pointed out He had tried to count but could only between theory and experiment. The by Miklos Gyulassy in his talk on find eight forerunners - Bielefeld phenomenological modelling of QCD transport theory, the possibility (1982), Brookhaven (1983), Helsinki heavy ion collisions seems to repro­ of two different production mecha­ (1984), Asilomar (1986), Nordkirchen duce at least all the main features of nisms can affect the subsequent (1987), Lenox (1988), Menton the data with , resonances evolution of produced matter. (1990), Gatlinburg (1991), making and strings as the degrees of free­ Nuclear collision experiments have this year's meeting at Borlange the dom. However secondary interac­ reported an enhancement in the ninth. tions among the produced hadrons or yield at low transverse momentum The answer was given by Helmut strings need to be added. Hydrody- (less than 300 MeV/c). Four CERN Satz in his introductory talk, pointing namic calculations lead to results experiments (NA34, NA35, EMU05 out that at the of the Bielefeld which reproduce the main features of and NA44) and three at Brookhaven meeting, a few conferences dealing the collisions. (E810, E802/859/866 and E814) with similar topics had already been With increasing collision , the have studied single distribu­ held. parton degrees of freedom become tions under these conditions. The Bielefeld organizers thus did more important. Klaus Geiger Jehanne Simon-Gillo concluded that not consider their conference the described an ambitious scheme the Brookhaven results are well first. Whatever its pedigree, the treating the whole nucleus-nucleus described by models incorporating Borlange meeting covered collision in terms of a kinetic parton resonances. However the CERN production in highly excited and (quark/) cascade. The initial results are not fully understood, compressed , fluctua­ parton distribution at the beginning of leaving room for further speculations. tions and correlations, quark phe­ the collision is determined from the Johanna Stachel reported a mysteri­ nomena ( chromodynamics - quark-gluon and the ous and significant low transverse QCD) in nuclear collisions, probes evolution is followed in terms of momentum enhancement in and signatures of Quark-Gluon perturbative QCD. E814. (QGP), future collider experi­ These calculations, as well as The role of interferometry using ments and instrumentation. several others reported, reflect the identical was emphasized The theoretical talks were split ongoing effort to go beyond the by Scott Pratt. Without knowing the between the fundamental properties simplified treatment of the initial and lifetime of the produced

CERN Courier, December 1993 31 CENTRAL COLLISIONS at 14.6 A.GeV/c 0.30 In heavy ion collisions at Brookhaven (£802/ 866) the positive kaon/pion ratio increases with increasing projectile .

0.25

Au+Au (Central) 0.20 -

Si+Au (Central) + thermal (kinetic) equilibrium. The total number of strange particles 0.15 Si+Al (Central) could be unexpectedly high. Carlos Lourengo from NA38 pre­ sented new results on pair production below the J/psi reso­ 0.10 nance. In proton-proton and proton- Si+Al (Peripheral) nucleus collisions this can be under­ stood in terms 6f known sources like Drell-Yan pairs and semileptonic 0.05 decays of . In sulphur-uranium collisions there is a clear and unexplained excess of 0.00 pairs, significant since it is difficult to produce such heavy pairs in second­ 0.5 1.0 1.5 2.0 2.5 ary hadronic collisions. The psi Rapidity prime/J-psi ratio is found to be about 2% independent of the target mass in proton-nucleus collisions. This ratio decreases when going from proton- matter there can be no reliable QGP cooling may result in droplets to sulphur-uranium reac­ determination of the of , or ''. tions. The first phi in heavy or the dynamics of the collision. The possibility of producing meta- ion collisions at Brookhaven were Many heavy ion experiments (NA35, stable (stable against strong decays) reported by George Stephans NA44, WA80, E802/E859 and E814) strange plasma droplets was re­ (E859). presented data on two-particle viewed by Carsten Greiner. This is are considered to be a interferometry. Tom Humanic (NA44) speculative, but metastable hyper- sensitive probe of QGP formation. reported on multi-dimensional analy­ nuclei with several , called Rainer Santo from WA80 showed an sis of identified hadrons. As in many 'memos', seem quite likely from excess of photons in central sulphur- other experiments, NA44 finds a standard nuclear model calculations. collisions. The CERES (NA45) significant difference in the observed E810, E858/E878 and NA52 gave collaboration observes no such radii depending on whether or upper limits for production. excess. WA80 also presented the are measured. NA35, NA36, WA85, E810, E859 first spectra of eta mesons. The The radii for equivalent systems and E866 reported on strange neutral pion and eta transverse mass measured at Brookhaven (E802) are particle production. David Evans from spectra are remarkably similar, significantly smaller than the CERN WA85 presented data on strange and supporting the phenomenological results, showing that with increasing multistrange antibaryons, difficult to concept of transverse mass scaling. energy the interacting sys­ produce hadronically. Some In his review, Joe Kapusta dis­ tems expand. There is a significant antihyperon yields are more than cussed the importance of the early radius/transverse momentum de­ three those seen in proton- dense stage of the collision for pendence of the pairs observed. A proton interactions. Omega minus electromagnetic emission from similar effect is also seen by NA35 at (particle and ) candidates parton interactions and pointed out CERN. have been reported by WA85 for the the possibility of using measure­ Dieter Rohrich (NA35) mentioned first time. ments of lepton pairs in the J/psi to that in head-on nucleus-nucleus In gold-gold collisions the measure­ upsilon mass range to study partons collisions a large net density ment of strange particles is important approaching thermal equilibrium by is piled up in the central region. Shiva and the positive kaon/pion ratio redistributing their momenta in Kumar (E858/E878) reported that the increases with increasing projectile secondary collisions. This, as well as yields scale as the number mass. Ulrich Heinz reported on a the use of the photons as probes of of interacting projectile . based on secondary parton collisions, will

32 CERN Courier, December 1993 Rutherford Appleton Laboratory ARTICLE PHYSIOS

The Department of the Rutherford to operate in a large multi-national collaboration Appleton Laboratory has a vacancy for a Support is essential. Physicist to work on its experimental programme. The appointment will be at Higher Scientific The Department is engaged in research at CERN Officer level. Candidates should have a first or and DESY and other Institutes abroad. upper second class honours degree and several The successful applicant will be involved in years relevant post graduate experience, detector development and apparatus design for an preferably in the of experiment planned for the physics. It is anticipated that the successful at CERN. There will also be an opportunity to candidate will be under 30 years of age. spend a proportion of time analysing data from The salary range for a Higher Scientific Officer is one of the current experiments. He or she will be £13,025 to £18,911 pa. Progression up to £23,009 required to work closely with other members of the per annum can be acheived by a series of Department, to collaborate with staff from increases linked to annual performance Universities and other institutes both in the UK assessments. and abroad and be prepared to spend a significant fraction of time working overseas, if necessary. There is a non-contributory pension scheme. The ability to communicate effectively and

For an application form please contact the Recruitment Office, Personnel and Training Division, and Engineering Research Council, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX. Tel: 0235 445435 quoting reference VN 1202. Applications must be returned by: 24th December 1993. SERC is working towards equal opportunities and a smoke free workplace. IA8251

Department of Physics YORK UNIVERSITY - ZEUS Stanford University

The Department of Physics at Stanford University APPLICATIONS are invited for research seeks to make a junior level, tenure-track ap­ associate position with the ZEUS project. pointment in the field of Experimental Particle The successful applicant will help to run the Physics. It is likely that an additional appointment ZEUS experiment in DESY, develop and will be made in the field after the initial position is filled. install hardware for the upgrade of the ZEUS The Department pursues research in fundamental detector, and develop software for the physics and maintains a strong teaching program analysis of physics data. Applicants must at all levels. have a recent Ph.D. in experimental particle Candidates will be expected to have demonstrated physics. Send application, including curricu­ originality and the ability to carry outan independent lum vitae, details of hardware and software research program, along with a commitment to experience to : teaching. Stanford University actively seeks applications from women and minority candidates and is an Department of Physics & , affirmative-action employer. Petrie 128, York University, 4700 Keele Interested applicants should send their curriculum Street, North York, On. M3J 1P3. vitae and bibliography plus the names of at least three references to : Applicants should have 3 references send Professor Stanley G. Wojcick letters of recommendation under separate Depart, of Physics - Stanford University Stanford / CA 94 305-4060 cover. In accordance with Immigration regu­ The deadline for the applications will be lations, this advertisement is directed to March 1, 1994. Canadian citizens and permanent residents.

CERN Courier, December 1993 33 Experimental Research Associate Positions Centre for Subatomic Research UNIVERSITY OF ALBERTA The Subatomic Physics group at the University of Alberta has several openings for experimental Research Associates in Intermediate and High Energy physics. The group's present activities include : the HERMES spin structure function measurements at HERA; the OPAL collaboration at LEP; the ATLAS project for the LHC at CERN; the E787 rare kaon-decay tests of the at Brookhaven; violation in pp scattering, np breaking, and nuclear reaction studies at TRIUMF; and photonuclear studies at the Saskatchewan Accelerator Laoboratory. Several appointments will be made for candidates who have received their degrees within the last two years. The successful candidates will have some freedom to define their research activities but a major contribution in those projects is expected. Salary will be commensurate with experience. Given satisfactory on-going performance, new Research Associates are normally appointed for a three-year period, but we are also seeking a more experienced candidate and may fill a position without fixed term. For this latter position we are particularly looking for physicists with hardware experience in detector design and construction and/or fast trigger . Candidates should send their resume and names of at least three references to

Research Associate Search Committee Centre for Subatomic Research, University of Alberta, Edmonton, Alberta, CanadaT6G 2N5 Applications should be received by 15 February 1993. In accordance with Canada Employment regulations this advertisement is directed at Canadian citizens and landed immigrants, but all qualified candidates are encouraged to apply.

BROOKHAVEN TECHNISCHE HOCHSCHULE NATIONAL LABORATORY AACHEN Am III. Physikalischen InstitutderRWTH Aachen PHYSICS DEPARTMENT ist die Stelle The Physics Department is searching for a physicist to lead eines() Hochschulassistenten(in) (CI) the scientific group associated with the STAR experiment at Brookhaven National Laboratory's Relativistic Heavy Ion ab sofort zu besetzen. Arbeitsgebiet ist die Collider, RHIC. This large collaborative experiment is based upon a large Time Projection Chamber (TPC), and the experimentelle Teilchenphysik, speziell die Brookhaven responsibilities include the design and con­ Datenanalyse und Mitarbeit innerhalb des OPAL- struction of the solenoidal , the development of the silicon vertex tracker, leadership of the software and data Experiments am Speicherring LEP bei CERN in acquisition systems as well as development of very forward Genf. Schwerpunkte der Forschungsrichtung angle external TPC's. Applicants to lead the Brookhaven STAR group should have extensive experience in nuclear or sollten experimentelle Studien der Starken high energy experimental physics, have had some manage­ Wechselwirkung und/oder die Suche nach neuen ment experience in large experiments and would be expect­ Teilchen bei LEP-II sein. Die Position erfordert ed to participate significantly in the overall management of the STAR collaboration. eine angemessene Beteiligung an der Lehre in Candidates should submit a curriculum vitae and the names Aachen sowie mehrere, auch ausgedehnte of three references to: Dr. P.D. Bond, Chairman, Physics Aufenthalte in Genf. Vorausgesetztwerden eine Department, Brookhaven National Laboratory, Associated Universities, Inc., P. 0. Box 5000, Upton, Long Island, NY uberdurchschnittliche Promotion in exp. 11973-5000. Equal Opportunity Employer M/F/D/V. Teilchenphysik sowie Erfahrung im Betrieb von Grossexperimentenundderdamitverbundenen Il III BROOKHAVEN Verwaltung, Verarbeitung und Analyse von Daten und Modellrechnungen auf verschiedenen rill! NATIONAL LABORATORY Rechnersystemen. Bewerbungen mit den M M I ASSOCIATED UNIVERSITIES, INC. ublichen Unterlagen werden erbeten an at the center of science, beside the sea Prof. Dr. S. Bethke, Physikalisches Institut MIA, RWTH Physikzentrum, D- 52056 Aachen.

34 CERN Courier, December 1993 crucially depend on the detailed chairman. Germany was selected to understanding of different back­ host the 12th conference in this grounds. series. The character of the QGP External transitions is still not completely From Ingvar Otterlund and Vesa correspondents clear. argued that Ruuskanen with two massless quarks QCD has Argonne National Laboratory, (USA) resemblances to the four-component D. Ayres Heisenberg antiferromagnet with its Brookhaven, National Laboratory, (USA) rather well known properties. This P. Yamin means that critical properties close to CEBAF Laboratory, (USA) the critical can be S. Corneliussen calculated precisely in QCD. Cornell University, (USA) D. G. Cassel While a comprehensive review of DESY Laboratory, (Germany) lattice calculations was not included P. Waloschek in the programme, some of the Fermi National Accelerator Laboratory, confusion on the behaviour and (USA) of excitations close to the J. Cooper, J. Holt critical temperature was clarified. GSI Darmstadt, (Germany) According to the results presented by G. Siegert Graham Boyd, correlations in INFN, () mesonic channels are observed also A. Pascolini above the critical temperature, but IHEP, Beijing, (China) Qi Nading the bound states disappear. JINR Dubna, (Russia) In his experimental summary B. Starchenko Emanuele Quercigh said a 'heavy ion KEK National Laboratory, (Japan) age' had begun in Spring 1992 with S. Iwata gold beams at Brookhaven and will Lawrence Berkeley Laboratory, (USA) continue with lead beams at the CERN Courier B. Feinberg CERN SPS, while further ahead lie Los Alamos National Laboratory, (USA) the comprehensive collider pro­ contributions C. Hoffmann grammes, with the major STAR and Novosibirsk, Institute, (Russia) PHENIX experiments at Brook- The Editor welcomes contribu­ V. Balakin haven's RHIC, and ALICE at CERN's tions. As far as possible, text Orsay Laboratory, (France) Anne-Marie Lutz future LHC. Seeing the quark gluon should be sent via electronic plasma still needs hard work but PSI Laboratory, () mail. R. Frosch there are good reasons for optimism. The address is Rutherford Appleton Laboratory, (UK) At Quark Matter '93 a booklet 'High courier@cernvm..ch Jacky Hutchinson Energy Heavy Ion Experiments' was Plain text (ASCII) is preferred. Saclay Laboratory, (France) distributed, providing details of Illustrations should follow by Elisabeth Locci current high energy heavy ion experi­ mail (CERN Courier, 1211 IHEP, Serpukhov, (Russia) ments. It can be ordered from Evert 23, Switzerland). Yu. Ryabov Stenlund, Lund, (e-mail: Contributors, particularly Stanford Linear Accelerator Center, (USA) [email protected], fax +46 conference organizers, con­ M. Riordan 46104015). templating lengthy efforts Superconducting Super Collider, (USA) N. V. Baggett The 11th Conference on Ultra- (more than about 500 words) Relativistic Nucleus-Nucleus Colli­ should contact the Editor (by TRIUMF Laboratory, (Canada) M. K. Craddock sions (Quark Matter '95) will be held e-mail, or fax +41 22 782 1906) in Monterey, California, in January beforehand. 1995 with Art Poskanzer, LBL, as

CERN Courier, December 1993 35