Evidence for a soft nuclear equation-of-state from Kaon production in heavy-ion collisions

The production of pions and kaons has been measured in Au-197 + Au-197 collisions at beam energies from 0.6 to 1.5A GeV with the kaon spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au + Au collisions by factors up to 6 relative to C + C reactions, whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au + Au and C + C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.