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 $R_{Ψ_{2}}$ -- 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 $f_{\rm CME}=Δγ_{\rm CME}/Δγ$, which renders the $Δγ$-correlator insensitive to values of the Fourier dipole coefficient $a_1 \lesssim 2.5\%$, that is larger than the purported signal(signal difference) for ion-ion(isobaric) collisions. By contrast, the $R_{Ψ_{2}}$ correlator indicates concave-shaped distributions with inverse widths ($\mathrm{σ^{-1}_{R_{Ψ_2}}}$) that are linearly proportional to $a_1$, and independent of the character of the event plane used for their extraction. The sensitivity of the $R_{Ψ_{2}}$ correlator to minimal CME-driven charge separation in the presence of realistic backgrounds, could aid better characterization of the CME in heavy-ion collisions.