Measurement of charge multiplicity asymmetry correlations in high-energy nucleus-nucleus collisions at √sNN=200 GeV
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 √sNN=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, Δ, 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 vobs2), where Δ=[1.3±1.4(stat)+4.0−1.0(syst)]×10−5+[3.2±0.2(stat)+0.4−0.3(syst)]×10−3vobs2 for 20–40% Au + Au collisions. The implications for the proposed chiral magnetic effect are discussed.