Freeze-Out Parameters in Central 158AGeV Pb+Pb Collisions

Abstract

Neutral pion production in central 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. The pi0 transverse mass spectrum has been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out.