Strange Mesons as Probe for Dense Nuclear Matter

The production and propagation of kaons and antikaons has been studied in symmetric nucleus-nucleus collisions in the SIS energy range. The ratio of the excitation function of K⁺ production in Au+Au and C+C collisions increases with decreasing beam energy. This effect was predicated for a soft nuclear equation-of-state. In noncentral Au+Au collisions, the K⁺ mesons are preferentially emitted perpendicular to the reaction plane. The K^-/K⁺ ratio from A+A collisions at beam energies which are equivalent with respect to the threshold is found to be about two orders of magnitude larger than the corresponding ratio from proton-proton collisions. Both effects are considered to be experimental signatures for a modification of kaon properties in the dense nuclear medium.