A sensitivity study of the primary correlators used to characterize chiral-magnetically-driven charge separation

Abstract

A Multi-Phase Transport (AMPT) model is used to study the detection sensitivity of two of the primary correlators – Δγ and RΨ2 – employed to characterize charge separation induced by the Chiral Magnetic Effect (CME). The study, performed relative to several event planes for different input “CME signals”, indicates a detection threshold for the fraction fCME=ΔγCME/Δγ, which renders the Δγ-correlator insensitive to values of the Fourier dipole coefficient a1≲2.5%, that is larger than the purported signal (signal difference) for ion-ion(isobaric) collisions. By contrast, the RΨ2 correlator indicates concave-shaped distributions with inverse widths (σRΨ2−1) that are linearly proportional to a1, and independent of the character of the event plane used for their extraction. The sensitivity of the RΨ2 correlator to minimal CME-driven charge separation in the presence of realistic backgrounds, could aid better characterization of the CME in heavy-ion collisions.