Final state effects on charge asymmetry of pion elliptic flow in high-energy heavy-ion collisions

Within a multi-phase transport (AMPT) model with the string melting mechanism and imported initial electric quadrupole moment, the difference between the elliptic flow of positive and negative pions is calculated. The slope parameter r   of the linear dependence of Δv2=v2(π−)−v2(π+)Δv2=v2(π−)−v2(π+) on Ach=(N+−N−)/(N++N−)Ach=(N+−N−)/(N++N−) is yielded owing to the parton cascade, which converts the initial electric quadrupole distribution into the final charge-dependent elliptic flow. The slope parameter r is found to be increased by the hadronization given by the coalescence, and decreased by the resonance decays. The slope parameter r is very sensitive to both the initial electric quadrupole percentage and centrality bin and consequently a helpful constraint on the quadrupole moment of the chiral magnetic wave is obtained for Au + Au collisions at the top RHIC energy.