Survey of experimental data

Abstract

A review of meson emission in heavy-ion collisions at incident energies from SIS up to collider energies is presented. A statistical model assuming chemical equilibrium and local strangeness conservation (i.e. strangeness conservation per collision) explains most of the observed features.Emphasis is put on the study of K+ and K− emission at low incident energies. In the framework of this statistical model it is shown that the experimentally observed equality of K+ and K− rates at ‘threshold-corrected’ energies √s − √sth is due to a crossing of two excitation functions. Furthermore, the independence of the K+/K− ratio from the number of participating nucleons observed between SIS and RHIC is consistent with this model.It is demonstrated that the K− production at SIS energies occurs predominantly via strangeness exchange and that this channel approaches chemical equilibrium. The observed maximum in the K+/π+ excitation function is also seen in the ratio of strange to non-strange particle production. The appearance of this maximum around 30 A GeV is due to the energy dependence of the chemical freeze-out parameters T and μB.