Temperatures and non-ideal expansion in ultrarelativistic nucleus-nucleus collisions

The hadronic phase space distributions calculated with the transport model RQMD for central S (200 AGeV) on S and Pb (160 AGeV) on Pb collisions are analyzed to study the deviations from ideal hydrodynamical evolution. After thermalization, the source stays in approximate kinetic equilibrium for about 2 fm/c at a temperature close to 140 MeV. The freeze-out state resembles a thermal system at a temperature of 130 MeV. This freeze-out temperature is lower than values derived from fits to measured particle ratios and transverse momentum spectra. The processes in RQMD to which the differences can be attributed to are the absence of chemical equilibrium at freeze-out and the non-ideal expansion of the hadronic matter. The collective flow velocities of heavier particles are smaller by about 20 to 30% in comparison to the dominantly pionic fluid.