Chemical non-equilibrium and deconfinement in 200 A GeV Sulphur induced reactions

Abstract

We interpret hadronic particle abundances produced in S--Au/W/Pb 200 A GeV reactions in terms of the final state hadronic phase space model and determine by a data fit of the chemical hadron freeze-out parameters. Allowing for the flavor abundance non-equilibrium a highly significant fit to experimental particle abundance data emerges, which supports possibility of strangeness distillation. We find under different strategies stable values for freeze-out temperature T_f=143\pm3 MeV, baryochemical potential \mu_B= 173\pm6 MeV, ratio of strangeness (\gamma_s) and light quark (\gamma_q) phase space occupancies \gamma_s/\gamma_q=0.60\pm0.02, and \gamma_q=1.22\pm0.05 without accounting for collective expansion (radial flow). When introducing flow effects which allow a consistent description of the transverse mass particle spectra, yielding |v_c|=0.49\pm0.01c, we find \gamma_s/\gamma_q=0.69\pm0.03, \gamma_q=1.41\pm0.08. The strange quark fugacity is fitted at \lambda_s=1.00\pm0.02 suggesting chemical freeze-out directly from the deconfined phase.