Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c

TL;DR

This study measures two-particle correlations in Pb-Pb collisions at 158 GeV/c, revealing how the collision centrality affects the size, expansion velocities, and temperature of the fireball at freeze-out.

Contribution

It introduces a Coulomb correction for expanding sources and reconstructs the fireball's properties as a function of collision centrality.

Findings

Less central collisions have slower expansion velocities.

Expansion duration is shorter in less central collisions.

System freeze-out occurs at smaller sizes and higher temperatures.

Abstract

Two-particle correlation functions of negatively charged hadrons from Pb-Pb collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment at the CERN SPS. A Coulomb correction procedure that assumes an expanding source has been implemented. Within the framework of an expanding thermalized source model the size and dynamical state of the collision fireball at freeze-out have been reconstructed as a function of the centrality of the collision. Less central collisions exhibit a different dynamics than central ones: both transverse and longitudinal expansion velocities are slower, the expansion duration is shorter and the system freezes out showing smaller dimensions and higher temperature.