Results from FOPI on strangeness production and propagation at SIS energies

Heavy ion collisions at SIS energies (1–2 A GeV) offer a unique tool to probe the properties of hot and dense nuclear matter. In particular, the partial restoration of chiral symmetry is predicted to lead in this energy range to in-medium modifications of hadron properties. Strange particle production below or close to the threshold energy is a useful probe to investigate these inmedium effects. The FOPI collaboratio nh as recently measured the production and the propagation of charged and neutral strange particles. The K + production probability is investigated as a function of the system size at a beam energy of 1.5 A GeV. Results on K 0 production as well as K − /K + ratio as a function of rapidity in Ru+Ru collisions at 1.69 A GeV are presented. In addition, the sideward flow of charge da ndneutral strange particles has been measured. Results are compared with predictions of transport calculations (BUU and IQMD).