Rapidity and energy dependence of the electric charge correlations in A+A collisions from 20A to 158A GeV

Abstract

Results from electric charge correlations studied with the Balance Function (BF) method in A+A collisions from 20A to 158A GeV are presented in two different rapidity intervals: In the midrapidity region we observe a decrease of the width of the BF 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 BF expressed by the normalized width parameter W increases with energy toward the highest CERN Super Proton Synchrotron and BNL Relativistic Heavy Ion Collider energies. Finally we compare our experimental data points with the predictions of several models. The hadronic string models Ultra-relativistic Quantum Molecular Dynamics and Heavy Ion Jet INteraction Generator (HIJING) do not reproduce the observed narrowing of the BF. However, A MultiPhase Transport medel (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 BF analysis to the time of hadronization.