Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon

TL;DR

This study measures event-by-event fluctuations in average transverse momentum in Pb+Pb collisions at 158 GeV per nucleon, providing insights into collision dynamics and potential signals of QCD phase transition.

Contribution

It offers the first data on transverse momentum fluctuations in these collisions, testing microscopic and thermodynamic models and constraining theories of chiral symmetry restoration.

Findings

Observed fluctuations are consistent with independent particle production plus known correlations.

Limits are set on non-statistical fluctuation models, especially those related to chiral symmetry restoration.

A significant parameter space for isospin fluctuation models is excluded by the data.

Abstract

We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.