Possible origin of the different behaviors of the K⁺/π⁺ and the K^-/π^- excitation functions

The beam energy dependences of the K⁺/π⁺ and the K^-/π^- yield ratios in relativistic heavy-ion collisions are explained in the framework of the statistical thermal model from Heavy Ion Synchrotron to Relativistic Heavy Ion Collider energies. The completely different behaviors between positive and negative charges, which were first observed experimentally, are a natural outcome of the model with a proper choice of the freeze-out temperature and chemical potentials. We will also compare the kaon and pion yields with the elementary p + p data scaled by the number of participant nucleons. This analysis shows an enhancement of kaons at Super Proton Synchrotron energies, but a suppression of pions at Alternate Gradient Synchrotron and Relativistic Heavy Ion Collider energies.