Measurement of Charge Multiplicity Asymmetry Correlations in High Energy Nucleus-Nucleus Collisions at 200 GeV

TL;DR

This paper measures charge asymmetry correlations in high-energy gold-gold collisions at 200 GeV, revealing charge separation related to the event plane and ellipticity, with implications for the chiral magnetic effect.

Contribution

It provides new quantitative measurements of charge asymmetries and their dependence on ellipticity, contributing to understanding the chiral magnetic effect in heavy-ion collisions.

Findings

Charge pairs are emitted back-to-back or same-side depending on sign.

Charge separation is largest near the event plane.

Charge asymmetry correlates with ellipticity, supporting chiral magnetic effect hypotheses.

Abstract

A study is reported of the same- and opposite-sign charge-dependent azimuthal correlations with respect to the event plane in Au+Au collisions at 200 GeV. The charge multiplicity asymmetries between the up/down and left/right hemispheres relative to the event plane are utilized. The contributions from statistical fluctuations and detector effects were subtracted from the (co-)variance of the observed charge multiplicity asymmetries. In the mid- to most-central collisions, the same- (opposite-) sign pairs are preferentially emitted in back-to-back (aligned on the same-side) directions. The charge separation across the event plane, measured by the difference, $\Delta$, between the like- and unlike-sign up/down $-$ left/right correlations, is largest near the event plane. The difference is found to be proportional to the event-by-event final-state particle ellipticity (via the observed second-order harmonic $v^{\rm obs}_{2}$), where $\Delta=(1.3\pm1.4({\rm stat})^{+4.0}_{-1.0}({\rm syst}))\times10^{-5}+(3.2\pm0.2({\rm stat})^{+0.4}_{-0.3}({\rm syst}))\times10^{-3}v^{\rm obs}_{2}$ for 20-40% Au+Au collisions. The implications for the proposed chiral magnetic effect are discussed.