Statistical model description of K+ and K− production between 1–10 A·GeV

The excitation functions of K+ and K− mesons in heavy ion collisions are studied within a statistical model assuming chemical and thermal equilibrium with exact strangeness conservation. At low incident energies the associate production of kaons, i.e., the production of a K+ together with a hyperon and the production of a K− together with a K+, implies specific features: different threshold energies and different dependences of K+ and K− yields on baryon number density. It is shown that the experimentally observed equality of the K+ and K− rates at energies s−sth≤0 is due to a crossing of the two excitation functions. Furthermore, the independence of the K+ to K− ratio on the number of participating nucleons observed at 1 and 10 A·GeV is consistent with this model.