Strangeness excitation functions and transition from baryonic to mesonic freeze-out

The sharp peak in the K+/π+ ratio in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model a rapid change is expected as the hadronic gas undergoes a transition from a baryon-dominated to a meson-dominated gas. The maximum in the Λ/π ratio is well reproduced by the Statistical Model, but the change in the K+/π+ ratio is somewhat less pronounced than the one observed by the NA49 collaboration. The calculated smooth increase of the K−/π− ratio and the shape of the Ξ−/π+ and Ω−/π+ ratios exhibiting maxima at different incident energies is consistent with the presently available experimental data. We conclude that the measured particle ratios with 20 − 30% deviations agree with a hadronic freeze-out scenario. These deviations seem to occur just in the transition from baryon-dominated to meson-dominated freeze-out.