2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/184696We argue that hadron multiplicities in central high energy nucleus-nucleus collisions are established very close to the phase boundary between hadronic and quark matter. In the hadronic picture this can be described by multi-particle collisions whose importance is strongly enhanced due to the high particle density in the phase transition region. As a consequence of the rapid fall-off of the multi-particle scattering rates the experimentally determined chemical freeze-out temperature is a good measure of the phase transition temperature.final version, some comments added about "statistical hadronization", to appear in Phys. Lett. BNuclear TheoryHigh Energy Physics - PhenomenologyNuclear Experimenttext