Hadron Production At Rhic - Chemical Freeze-Out, Effective Masses And Expanding Matter

The properties of the strongly interacting matter produced at RHIC are investigated within a chemical and thermal equilibrium chiral SU(3) sigma - omega approach. The focus is on the freeze-out conditions, the effective masses of the produced hadrons and the expansion of the system. For the freeze-out conditions the commonly adopted noninteracting gas calculations yield temperatures and chemical potentials close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parameterizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occurred in those collisions, "freezing" of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking.