K-/K+ ratio at GSI in hot and dense matter

The K-/K+ ratio in heavy-ion collisions at GSI energies is studied including the properties of the participating hadrons in hot and dense matter. The determination of the temperature and chemical potential at freeze-out conditions compatible with the ratio K-/K+ is very delicate, and depends on the approach adopted for the antikaon self-energy. Three approaches for the K- self-energy are considered: non-interacting K-, on-shell self-energy and single-particle spectral density. With respect to the on-shell approach, the use of an energy dependent K-bar spectral density, including both s- and p-wave components of the KbarN interaction, lowers considerably the freeze-out temperature and gives rise to the 'broad-band equilibration' advocated by Brown, Rho and Song