Central Pb+Pb Collisions at 158 A GeV/c Studied by Pion-Pion Interferometry

TL;DR

This study measures two-particle correlations of negative pions in central Pb+Pb collisions at 158 A GeV/c, revealing a boost-invariant expanding source with non-Gaussian correlation functions.

Contribution

It provides a detailed multi-dimensional analysis of pion-pion correlation radii, including resolution corrections and shape analysis, highlighting non-Gaussian features.

Findings

Correlation radii around 7 fm in all dimensions

Source exhibits boost-invariant expansion

Correlation functions are better modeled by exponentials

Abstract

Two-particle correlations have been measured for identified negative pions from central 158 AGeV Pb+Pb collisions and fitted radii of about 7 fm in all dimensions have been obtained. A multi-dimensional study of the radii as a function of kT is presented, including a full correction for the resolution effects of the apparatus. The cross term Rout-long of the standard fit in the Longitudinally CoMoving System (LCMS) and the vl parameter of the generalised Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a boost invariant expansion. The shapes of the correlation functions in Qinv and Qspace have been analyzed in detail. They are not Gaussian but better represented by exponentials. As a consequence, fitting Gaussians to these correlation functions may produce different radii depending on the acceptance of the experimental setup used for the measurement.