K+- and K--production in heavy-ion collisions at SIS energies

The production and the propagation of K+- and of K--mesons in heavyion collisions at beam energies of 1 to 2 A GeV have systematically been investigated with the Kaon Spectrometer (KaoS) at the SIS at the GSI. 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. At 1.5 A GeV 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. The spectral slopes and the polar emission patterns are different for K- and K+. These observations indicate that K+-mesons decouple earlier from the reaction zone than K--mesons.