Rapidity and energy dependence of the electric charge correlations in A+A collisions at the SPS energies

TL;DR

This study examines electric charge correlations in A+A collisions across various energies and rapidity intervals, revealing a narrowing of the Balance Function with increasing energy and centrality, and testing model predictions against experimental data.

Contribution

It provides new insights into the energy and rapidity dependence of charge correlations and evaluates the effectiveness of different theoretical models in reproducing observed phenomena.

Findings

Balance Function width decreases with collision centrality at mid-rapidity.

Narrowing of the Balance Function increases with collision energy.

AMPT model reproduces the observed narrowing, unlike UrQMD and HIJING.

Abstract

Results from electric charge correlations studied with the Balance Function method in A+A collisions from 20\emph{A} to 158\emph{A} GeV are presented in two different rapidity intervals: In the mid-rapidity region we observe a decrease of the width of the Balance Function distribution with increasing centrality of the collision, whereas this effect vanishes in the forward rapidity region. Results from the energy dependence study in central Pb+Pb collisions show that the narrowing of the Balance Function expressed by the normalised width parameter \textit{W} increases with energy towards the highest SPS and RHIC energies. Finally we compare our experimental data points with predictions of several models. The hadronic string models UrQMD and HIJING do not reproduce the observed narrowing of the Balance Function. However, AMPT which contains a quark-parton transport phase before hadronization can reproduce the narrowing of the BF's width with centrality. This confirms the proposed sensitivity of the Balance Function analysis to the time of hadronization.