Study of charge-dependent azimuthal correlations using reaction-plane-dependent balance functions

TL;DR

This study investigates charge-dependent azimuthal correlations in heavy-ion collisions, using reaction-plane-dependent balance functions across multiple energies, revealing that local charge conservation and elliptic flow can explain observed signals without invoking local parity violation.

Contribution

It introduces reaction-plane-dependent balance functions as a tool to interpret charge correlations, challenging the interpretation of signals as evidence of local parity violation.

Findings

Balance functions are sensitive to charge formation and diffusion.

Local charge conservation and elliptic flow explain the charge correlations.

Model reproduces most three-particle azimuthal correlations at 200 GeV.

Abstract

STAR has recently reported charge-dependent azimuthal correlations that are sensitive to the charge separation effect in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. Qualitatively, these results agree with some of the theoretical predictions for local parity violation in heavy-ion collisions. However, a study using reaction-plane-dependent balance functions shows an alternative origin of this signal. The balance function, which measures the correlation between oppositely charged pairs, is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. The reaction-plane-dependent balance function measurements can be related to STAR's charge-dependent azimuthal correlations. We report reaction-plane-dependent balance functions for Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200, 62.4, 39, 11.5, and 7.7 GeV using the STAR detector. The model of Schlichting and Pratt incorporating local charge conservation and elliptic flow reproduces most of the three-particle azimuthal correlation results at 200 GeV. The experimental charge-dependent azimuthal charge correlations observed at 200 GeV can be explained in terms of local charge conservation and elliptic flow.