Review of the results of the KaoS collaboration

The production of K+ and of K− mesons in heavy-ion collisions at beam energies of 1 to 2 A GeV has systematically been investigated with the kaon spectrometer KaoS. The ratio of the K+ production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. A comprehensive study of the K+ and of the K− emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K−/K+ ratio is found to be nearly constant as a function of the collision centrality and can be explained by the dominance of strangeness exchange. On the other hand, the spectral slopes and the polar emission patterns are different for K− and for K+. Furthermore the azimuthal distribution of the particle emission has been investigated. K+ mesons and pions are emitted preferentially perpendicular to the reaction plane as well in Au+Au as in Ni+Ni collisions. In contrast for K− mesons in Ni+Ni reactions an in-plane flow was observed for the first time at these incident energies.