Strangeness in ultrarelativistic nucleus-nucleus collisions

Abstract

I discuss strangeness production in nucleus-nucleus reactions at ultrarelativistic energies (up to 200 AGeV). In these reactions matter may be created with densities and temperatures in the transition region between quark-gluon plasma (QGP) and hadron gas. Strange anti-baryon enhancement at 200 AGeV and probably even more so at 10 AGeV signals importance of interactions beyond hadron gas dynamics. The systematics of strangeness production indicates that energy and baryon density are key variables while the size of the production volume plays no visible role. Analysis of strangeness appears useful to explore thermalization, flow and the post-equilibrium stage in ultrarelativistic nucleus-nucleus collisions.