Thermal and hadrochemical equilibration in nucleus-nucleus collisions at the SPS

The currently available set of hadron abundances at the SPS for central S + Au(W,Pb) collisions is compared to predictions from a scenario assuming local thermal and hadrochemical equilibrium. The data are consistent with a freeze-out temperature T = 160–170 MeV. Spectra are consistent with this temperature range and a moderate transverse expansion. The freeze-out points at the AGS and SPS are found to be close to the phase boundary between a hadron gas and an ideal quark-gluon phase.