Possible observables for the chiral electric separation effect in Cu + Au collisions

Abstract

The quark-gluon plasma (QGP) generated in relativistic heavy-ion collisions could be locally parity-odd. In parity-odd QGP, the electric field may induce a chiral current which is called the chiral electric separation effect (CESE). We propose two possible observables for CESE in Cu + Au collisions: The first one is the correlation $ζ_{αβ}=\langle \cos[2(ϕ_α+ϕ_β-2Ψ_{\rm RP})]\rangle$; the second one is the charge-dependent event-plane angle $Ψ^{q}_2$ with $q=\pm$ being charge. Nonzero $Δζ=ζ_{opp}-ζ_{same}$ and $ΔΨ=\langle|Ψ_2^+-Ψ_2^-|\rangle$ may signal the CESE in Cu + Au collisions. Within a multiphase transport model, we study how the final state interaction affects these observables. We find that the correlation $γ_{αβ}=\langle\cos(ϕ_α+ϕ_β-Ψ_{\rm RP})\rangle$ is sensitive to the out-of-plane charge separation caused by the chiral magnetic effect and to the in-plane charge separation caused by the in-plane electric field, but it is not sensitive to the CESE. On the other hand, $Δζ$ and $ΔΨ$ are sensitive to the CESE. Therefore, we suggest that the future experiments measure the above observables in Cu+Au collisions in order to disentangle different chiral and charge separation mechanisms.