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

TL;DR

This paper proposes and analyzes specific observables in Cu + Au collisions to detect the chiral electric separation effect (CESE) in quark-gluon plasma, highlighting their sensitivity to CESE versus other charge separation phenomena.

Contribution

The study introduces two novel observables, $ riangle ilde{ ext{z}}$ and $ riangle ext{Psi}$, for detecting CESE and evaluates their effectiveness using a multiphase transport model.

Findings

$ riangle ilde{ ext{z}}$ and $ riangle ext{Psi}$ are sensitive to CESE.

The correlation $ ext{gamma}_{ ext{alpha}eta}$ is not sensitive to CESE.

Final state interactions influence the observables.

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 $\zeta_{\alpha\beta}=\langle \cos[2(\phi_\alpha+\phi_\beta-2\Psi_{\rm RP})]\rangle$; the second one is the charge-dependent event-plane angle $\Psi^{q}_2$ with $q=\pm$ being charge. Nonzero $\Delta\zeta=\zeta_{opp}-\zeta_{same}$ and $\Delta\Psi=\langle|\Psi_2^+-\Psi_2^-|\rangle$ 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 $\gamma_{\alpha\beta}=\langle\cos(\phi_{\alpha}+\phi_{\beta}-\Psi_{\rm RP})\rangle$ 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, $\Delta\zeta$ and $\Delta\Psi$ 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.