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Description
9:00-9:30 Sonja Kabana (Univ. Bern) for the NA52 collaboration
Charged kaon production in Pb+Pb collisions at 158 A GeV measured with the NA52 experiment
We present the dependence of charged kaon yields produced in Pb+Pb collisions at 158 A GeV, on the number of nucleons participating in the collision (N). We observe the onset of 'kaon enhancement' with respect to p+Be and the most peripheral Pb+Pb collisions, near N=80. This onset may be associated with a QCD phase transition. We discuss how the NA52 data compare to results from other experiments.
9:30-10:00 Adam Jacholkowski (Univ. of Bari) for the NA57/WA97 collaboration
Strangeness production study in the NA57 experiment
The NA57 experiment has been designed to study the onset of the strange baryon and antibaryon enhancements in PbPb with respect to pBe collisions, first observed by the WA97 experiment at 160 A GeV/c beam momentum. The aim is to look for the dependence of these enhancements on: the interaction volume, as measured by the number of wounded nucleons i.e. those nucleons which undergo at least one primary inelastic scattering with another nucleon the collision energy per incoming nucleon. The window of geometrical acceptance of NA57 is similar to that of WA97. NA57, however, extends its centrality range down to a lower limit of about 50 wounded nucleons, while the corresponding limit in WA97 was about 100 . In addition, NA57 has collected data both at 160 and at 40 A GeV/c, while WA97 collected data only at the top SPS beam momentum of 160 A GeV/c. We present the first results on strange baryon production and comment on the forthcoming analysis.
coffee break
10:15-10:30 Thorsten Kollegger (IKF, Frankfurt) for the NA49 collaboration
Strange particle production in A+A collisions from NA49
Data on strange particle production from NA49 will be presented. In particular, strangeness yields in central Pb+Pb collisions at 40 AGeV will be shown. Together with lower (AGS) and higher (top-SPS, RHIC) energies, they indicate a non-monotonic behaviour of the K+/pi+ ratio.
The interesting energy region is located at lower SPS energies (20-80
AGeV). In addition, we present data on the system size dependence of the production of strange hadrons (kaons, lamdba(1520)).
10:30-11:00 Tatjana Susa (Institute Rudjer Boskovic, Zagreb) for the NA49 collaboration
Strangeness production in p+p and p+A collisions from NA49
Xi- and antiXi+ baryons have been measured with the NA49 detector over a wide range of hadronic reactions making use of full pt coverage in a cms rapidity interval from -1.0 to +1.0 units. The first measurement of pt and y distributions over this acceptance interval in p+p interactions, as well as centrality-controlled p+Pb reactions is presented. Rapidity distribution of Xi- and antiXi+ in central PbPb collisions and a comparative study of antiXi+ over Xi- ratio in all these reactions will be discussed.
11:00-11:15 Karel Safarik (CERN)
Comments on pp and pA strangeness production
Data on strangeness production in pp and pA collisions are of crucial importance in understanding of strangeness enhancement in AA collisions. We will review the experimental situation in pp and pA interactions at high energies and discussed the proposed interpetations and implications for AA collisions.
11:15 Jan Rafelski (Univ. Arizona, Tucson)
Strange Hadrons and their resonances as a diagnostic tool of freeze-out dynamics
We show in an analysis of the yield of hadrons and the shape of strange baryon and antibaryon spectra that hadronic particles must have been produced in a sudden process with a common condition for chemical and thermal freeze-out. In order to experimentally and directly distinguish between sudden nonequilibrium, and smooth reequilibration hadronization, we propose to explore strange hadron resonance production, (e.g.K*(892), Lambda(1520) and Sigma(1385) ). We demonstrate that using the yields relative to Kaons, and Lambda respectively, the two key physical parameters, the hadronization temperature and hadronization time can be obtained. Work carried out in collaboration with Jean Letessier (Paris) and Giorgio Torrieri (Tucson)
lunch break
14:00-14:30 Krzysztof Redlich (GSI, Germany and Univ. Wroclaw, Poland)
Statistical Hadronization and Strangeness Enhancement in Heavy Ion Collisions
The strange and non strange hadron production in heavy ion collisions will be discussed in very broad energy range from SIS up to RHIC. We argue that the available data are showing a high degree of hadrochemical equilibration and we derive unified conditions for chemical freezeout. We show, on the basis of kinetic evolution equation, that the consistent treatment of strangeness equilibration at low collision energy or in peripheral heavy ion collisions at SPS require canonical formulation of strangeness conservation. We argue that the observed enhancement of strange baryons and antibaryons yield in central A-A relative to p-p or p-A collisions can be possibly explained in terms of the statistical model as the passage from the grand canonical to canonical equilibrium limit. The specific centrality dependence of multistrange baryons as a signal for deconfinement will be also discussed.
14:30-15:00 Helmut Oeschler (Darmstadt University of Technology, Germany)
Strange Particle Production from SIS up to AGS
A review of strange particle production in heavy ion collisions at incident energies up to 40 AGeV is presented. It is shown how the
shape of the spectra and the various particle yields vary with system size, with centrality and with incident energy. A statistical model assuming chemical equilibrium and local strangeness conservation explains most of the observed features. Emphasis is put to the study of K+ and K- emission. Their very different behaviour at low incident energies can be explained by the canonical formulation of the statistical model. The independence of the K+ to K- ratio on the number of participating nucleons observed between SIS and RHIC energies is a strong argument for chemical equilibration. Furthermore, this model predicts a maximum of the strangeness content at incident energies around 30 AGeV.
Discussion
Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann
Organiser(s): Yiota Foka, Guy Paic and Urs Wiedemann