Strangeness Production in Nucleus-Nucleus Collisions at SPS Energies

Abstract

Hadron production in A+A collisions is studied by the CERN experiment NA49, in particular the dependence on collision energy and system size. Central Pb+Pb collisions were measured between 20 and 158 AGeV beam energy in order to localize the transition between collisions with a purely hadronic scenario and those with formation of a deconfined phase. At the highest energy (158 AGeV) the system size dependence was investigated in addition; this was done by varying the mass of the target-projectile combination or, alternatively, by selecting the impact parameter in non-central Pb+Pb collisions. In this report, special emphasis is put on the production of some of the most important strangeness carrying particles (charged kaons, A-baryons and Φ-mesons). The measured energy dependence of the total strangeness production normalized to the pion yield shows a distinct maximum at about 30 AGeV beam energy in central Pb+Pb collisions. This is interpreted as the transition point mentioned before. The system-size dependence at 158 AGeV is characterized by a fast rise with increasing number of participating nucleons reaching saturation at about 60 nucleons. This is ascribed to the vanishing of the canonical strangeness suppression in partonic systems with increasing size.