Hadronization of massive quark matter

We present a fast hadronization model for the constituent quark plasma (CQP) produced in relativistic heavy ion collisions at SPS. The model is based on rate equations and on an equation of state inspired by the string phenomenology. This equation of state has a confining character. We display the time evolution of the relevant physical quantities during the hadronization process and the final hadron multiplicities. The results indicate that the hadronization of CQP is fast.Comment: 12 pages, Latex, 2 EPS figures, contribution to the Proceedings of the 4th International Conference on Strangeness in Quark Matter (SQM'98), Padova, Italy, 20-24 July 199

Strange hyperon and antihyperon production from quark and string-rope matter

Hyperon and antihyperon production is investigated using two microscopical models: {\bf (1)} the fast hadronization of quark matter as given by the ALCOR model; {\bf (2)} string formation and fragmentation as in the HIJING/B model. We calculate the particle numbers and momentum distributions for Pb+Pb collisions at CERN SPS energies in order to compare the two models with each other and with the available experimental data. We show that these two theoretical approaches give similar yields for the hyperons, but strongly differ for antihyperons.Comment: 11 pages, Latex, 3 EPS figures, contribution to the Proceedings of the 4th International Conference on Strangeness in Quark Matter (SQM'98), Padova, Italy, 20-24 July 199

Signatures of Quark-Gluon-Plasma formation in high energy heavy-ion collisions: A critical review

A critical review on signatures of Quark-Gluon-Plasma formation is given and the current (1998) experimental status is discussed. After giving an introduction to the properties of QCD matter in both, equilibrium- and non-equilibrium theories, we focus on observables which may yield experimental evidence for QGP formation. For each individual observable the discussion is divided into three sections: first the connection between the respective observable and QGP formation in terms of the underlying theoretical concepts is given, then the relevant experimental results are reviewed and finally the current status concerning the interpretation of both, theory and experiment, is discussed. A comprehensive summary including an outlook towards RHIC is given in the final section.Comment: Topical review, submitted to Journal of Physics G: 68 pages, including 39 figures (revised version: only minor modifications, some references added

Directed and elliptic flow in 158GeV/nucleon Pb+Pb collisions

The directed and elliptic flow of protons and charged pions has been observed from the semicentral collisions of a 158 GeV/nucleon Ph beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low p(t). The elliptic flow of both is fairly independent of rapidity but rises with p(t)

Spectator nucleons in Pb+Pb collisions at 158 A center dot GeV

The composition of forward-going projectile spectator matter in fixed-target Pb+Pb collisions at 158 A.GeV at the CERN SPS has been studied as a function of centrality. The data were measured with the NA49 veto calorimeter. We observe that forward-going spectator matter in central collisions consists of 9 neutrons, 7 protons, and half a deuteron on average. At large impact parameters most spectator nucleons are bound in fragments. The relative resolution of the average impact parameter derived from the measurement of spectator neutrons is roughly 19% in the range from zero to half maximum impact parameters

Baryon stopping and charged particle distributions in central Pb+Ph collisions at 158 GeV per nucleon

Net proton and negative hadron spectra for central Pb + Pb collisions at 158 GeV per nucleon at the CERN Super Proton Synchrotron were measured and compared to spectra from lighter systems. Net baryon distributions were derived from those of net protons. Stopping (rapidity shift with respect to the beam) and mean transverse momentum [p(T)] of net baryons increase with system size. The rapidity density of negative hadrons scales with the number of participant nucleons for nuclear collisions, whereas their [p(T)] is independent of system size. The [p(T)] dependence upon particle mass and system size is consistent with larger transverse flow velocity at midrapidity for Pb + Pb compared to S + S central collisions

Xi and (Xi)over-bar production in 158 GeV/nucleon Pb+Pb collisions

We report measurements of Xi(-) and (Xi)over-bar(+) hyperon absolute yields as a function of rapidity in 158 GeV/c Ph + Pb collisions. At midrapidity, dN/dy = 2.29 +/- 0 12 for Xi(-), and 0.52 +/- 0.05 for (Xi)over-bar(+), leading to the ratio of (Xi)over-bar(+)/Xi(-) = 0.23 +/- 0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of T approximate to 300 MeV near mid-rapidity. The estimated total yield of Xi(-) particles in Pb+ Pb central interactions amounts to 7.4 +/- 1.0 per collision. Comparison to Xi(-) production in properly scaled p + p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Xi(-) production in Pb + Pb central collisions over elementary hadron interactions. (C) 1998 Elsevier Science B.V. All rights reserved

Event-by-event fluctuations of average transverse momentum in central Pb plus Pb collisions at 158 GeV per nucleon

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb + Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement. (C) 1999 Published by Elsevier Science B.V. All rights reserved