In-medium Production of Kaons at the Mean-Field Level

The in-medium mass and energy of kaons and antikaons are studied within the Relativistic Mean Field approach and compared with predictions from chiral models by taking care of kaon-nucleon scattering data. Implications for the subthreshold production of kaons and antikaons in heavy-ion collisions are discussed. We find only small corrections due to in-medium effects on the mean-field level for the relevant production processes for kaons. The production of kaons is even less favourable at high density due to repulsive vector interactions. We conclude that one has to go beyond mean-field approaches and take fluctuations and secondary production processes into account to explain the recently measured enhancement of kaon production at subthreshold energies. The situation is different for antikaons where in-medium effects strongly enhances their production rates. We also see strong in-medium modifications of the annihilation processes of antikaons and Lambda's which might be visible in flow measurements. At high density, we predict that the threshold energy for antikaon and Lambda production and annihilation become equal leading to similar numbers of antikaons and Lambda's in the dense zone of a relativistic heavy ion collision.