Strangeness equilibration in heavy ion collisions - art. no. 042201

Using a relativistic transport model for heavy ion collisions at energies t hat Lire below the threshold for kaon and antikaon production in nucleon-nu cleon collisions, we study how their abundances approach the canonical equi librium during the collisions. We find that kaons are far from chemical equ ilibrium at the initial and high density stage, and they approach equilibri um only during the expansion stage of the collisions when their production rate is small and becomes comparable to their annihilation rate. In contras t, antikaons approach chemical equilibrium much earlier but eventually fall out of equilibrium again as a result of their large annihilation cross sec tions in nuclear matter.