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Phase transition of a finite quarkgluon plasma
(1997)

Christian Spieles
Horst Stöcker
Carsten Greiner
 The deconfinement transition region between hadronic matter and quarkgluon plasma is studied for finite volumes. Assuming simple model equations of state and a first order phase transition, we find that fluctuations in finite volumes hinder a sharp separation between the two phases around the critical temperature, leading to a rounding of the phase transition. For reaction volumes expected in heavy ion experiments, the softening of the equation of state is reduced considerably. This is especially true when the requirement of exact colorsingletness is included in the QGP equation of state.

Chemical freezeout in relativistic A+A collisions: is it close to the QGP?
(1997)

Mark I. Gorenstein
Horst Stöcker
Granddon D. Yen
Shin Nan Yang
Walter Greiner
 Preliminary experimental data for particle number ratios in the collisions of Au+Au at the BNL AGS (11A GeV/c) and Pb+Pb at the CERN SPS (160A GeV/c) are analyzed in a thermodynamically consistent hadron gas model with excluded volume. Large values of temperature, T = 140 185 MeV, and baryonic chemical potential, µb = 590 270 MeV, close to the boundary of the quarkgluon plasma phase are found from fitting the data. This seems to indicate that the energy density at the chemical freezeout is tremendous which would be indeed the case for the pointlike hadrons. However, a selfconsistent treatment of the van der Waals excluded volume reveals much smaller energy densities which are very far below a lowest limit estimate of the quarkgluon plasma energy density. PACS number(s): 25.75.q, 24.10.Pa

Hadron production from a hadronizing quarkgluon plasma
(1997)

Christian Spieles
Horst Stöcker
Carsten Greiner
 Measured hadron yields from relativistic nuclear collisions can be equally well understood in two physically distinct models, namely a static thermal hadronic source versus a timedependent, nonequilibrium hadronization off a quark gluon plasma droplet. Due to the timedependent particle evaporation off the hadronic surface in the latter approach the hadron ratios change (by factors of / 5) in time. The overall particle yields then reflect time averages over the actual thermodynamic properties of the system at a certain stage of evolution.