Scaling properties of background- and chiral-magnetically-driven charge separation: evidence for detection of the chiral magnetic effect in heavy ion collisions

TL;DR

This study investigates charge separation in various heavy ion collisions to identify the chiral magnetic effect (CME), finding evidence of CME contributions in mid-central collisions through scaling violations in correlator measurements.

Contribution

It provides experimental evidence for CME in heavy ion collisions by analyzing scaling properties of charge separation correlators across different collision systems.

Findings

CME contributes approximately 27% to the charge separation signal in Au+Au collisions.

Scaling violations indicate the presence of CME in Au+Au, Ru+Ru, and Zr+Zr collisions.

Background-driven charge separation follows 1/N_{ch} scaling in smaller systems.

Abstract

The scaling properties of the $R_{\Psi_2}(\Delta S)$ correlator and the $\Delta\gamma$ correlator are used to investigate a possible chiral-magnetically-driven (CME) charge separation in $p$+Au, $d$+Au, Ru+Ru, Zr+Zr, and Au+Au collisions at $\sqrt s_{\mathrm{NN}}=200$~GeV, and in $p$+Pb ($\sqrt s_{\mathrm{NN}}=5.02$~TeV) and Pb+Pb collisions at $\sqrt s_{\mathrm{NN}}=5.02$ and $2.76$~TeV. The results for $p$+Au, $d$+Au, $p$+Pb, and Pb+Pb collisions, show the $1/{\rm N_{ch}}$ scaling for background-driven charge separation. However, the results for Au+Au, Ru+Ru, and Zr+Zr collisions show scaling violations which indicate a CME contribution in the presence of a large background. In mid-central collisions, the CME accounts for approximately 27\% of the signal + background in Au+Au and roughly a factor of two smaller for Ru+Ru and Zr+Zr, which show similar magnitudes.