Chemical nonequilibrium in high-energy nuclear collisions

Strange particles produced in S-Au/W/Pb 200 A GeV and Pb-Pb 158 A GeV react ions are described invoking final hadronic phase space in thermal equilibri um, but allowing chemical nonequilibrium. Several sets of statistical freez e-out parameters are obtained for each system, invoking different models of dense matter. We show that only when allowing for strange and nonstrange f lavour abundance nonequilibrium. a statistically significant description of the experimental results is obtained. Physical properties of the fireball at chemical freeze-out condition are evaluated and considerable universalit y of hadron freeze-out between the two different collision systems is estab lished. The relevance of the Coulomb effect in the highly charged Pb-Pb fir eballs for the chemical analysis are discussed. The influence of explosive collective matter flow is also described.