New correlator to detect and characterize the chiral magnetic effect

A charge-sensitive in-event correlator is proposed and tested for its efficacy to detect and characterize charge separation associated with the chiral magnetic effect (CME) in heavy ion collisions. Tests, performed with the aid of two reaction models, indicate discernible responses for background- and CME-driven charge separation, relative to the second- (${\mathrm{\Psi }}_2$) and third-order (${\mathrm{\Psi }}_3$) event planes, which could serve to identify the CME. The tests also indicate a degree of sensitivity which would enable robust characterization of the CME via anomalous viscous fluid dynamics (AVFD) model comparisons.

Figure 1

Comparison of the $R\left(\mathrm{\Delta }S\right)$ correlators for (a) background-driven charge separation ($a_1=0$) in 30–40% Au+Au collisions ($\sqrt{s_{NN}}=200\mathrm{GeV}$) obtained with the AMPT and AVFD models, and (b) the combined effects of background- and CME-driven ($a_1=1.0\%$) charge separation in Au+Au collisions obtained with the AVFD model at the same centrality and beam energy.

Figure 2

Comparison of the $R_{{\mathrm{\Psi }}_m}\left(\mathrm{\Delta }{S}^{\prime }\right)$ (a) and $R_{{\mathrm{\Psi }}_m}\left(\mathrm{\Delta }{S}^{\prime \prime }\right)$ (b) correlators for background-driven charge separation ($a_1=0$) in 30–50% Au+Au collisions ($\sqrt{s_{NN}}=200\mathrm{GeV}$) obtained with the AMPT model.

Figure 3

Comparison of the $R_{{\mathrm{\Psi }}_2}\left(\mathrm{\Delta }S\right)$ correlator for different input charge separation signals characterized by $a_1$, in 40–50% central Au+Au ($\sqrt{s_{NN}}=200\mathrm{GeV}$) events obtained with the AVFD model.

Figure 4

Comparison of the $R_{{\mathrm{\Psi }}_2}\left(\mathrm{\Delta }{S}^{\prime \prime }\right)$ correlator obtained from the analysis of (a) 10–20%, (b) 30–40%, and (c) 50-60% central AVFD events for Au+Au collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The curves represent Gaussian fits to the distributions. (d) $a_1$ vs ${\sigma }_{R_{{\mathrm{\Psi }}_2}}$ for the fits indicated indicated in (a)–(c).

Figure 5

Comparison of the $R_{{\mathrm{\Psi }}_2}\left(\mathrm{\Delta }S\right)$ correlators obtained from AVFD events with $a_1=1\%$ and 1.5%. The AVFD results are generated with an event plane resolution and $p_T$ and $\eta$ cuts, similar to the experimental ones [37].