Strangeness production in heavy ion collisions at SIS energies

The influence of the chiral mean field on the collective motion of kaons in relativistic heavy ion reactions, such as transverse flow, out-of-plane flow (squeeze-out) and radial flow, is investigated. The considered energy range (SIS energies) is 1-2 GeV/nucleon. The kaon dynamics is described with relativistic mean fields originating form chiral Lagrangians. The authors adopt a covariant quasi-particle picture including scalar and vector fields and compare this to a treatment with a static potential like force. The comparison to the available data (K+) measured by FOPI and KaoS strongly favors the existence of an in-medium potential. However, using full covariant dynamics makes it more difficult to describe the data which indicates that the mean field level is not sufficient for the description of the in-medium kaon dynamics