The Thermal Model and the Transition from Baryonic to Mesonic Freeze-Out

Abstract

The present status of the thermal model is reviewed and the recently discovered sharp peak in the $K^+/\pi^+$ ratio is discussed in this framework. It is shown that the rapid change is related to a transition from a baryon dominated hadronic gas to a meson dominated one. Further experimental tests to clarify the nature of the transition are discussed. In the thermal model the corresponding maxima in the Xi/pi and Omega/pi ratios occur at slightly different beam energies.