Thermal hadron production in relativistic nuclear collisions

We present the status of the description of hadron production in central nucleus-nucleus collisions within the statistical model . Extending previous studies by inclusion of very high-mass resonances (m>2 GeV), and the up-to-now neglected scalar $\sigma$ meson leads to an improved description of the data. In particular, the hitherto poorly reproduced energy dependence of the K+/pi+ ratio at SPS energies (“the horn”) is now well described through the connection to the hadronic mass spectrum and, implicitly, Hagedorn’s limiting temperature.