Test the chiral magnetic effect with isobaric collisions

TL;DR

This paper proposes using isobaric collisions at RHIC to distinguish the chiral magnetic effect signal from background effects, providing a clearer experimental test of CME in quark-gluon plasma.

Contribution

It demonstrates through simulation that isobaric collisions can effectively separate CME signals from background effects in heavy-ion collision experiments.

Findings

Over 10% difference in CME signal between Ru+Ru and Zr+Zr collisions.

Less than 2% difference in background effects between the two collision types.

Supports using isobaric collisions to identify the CME in experimental data.

Abstract

The quark-gluon matter produced in relativistic heavy-ion collisions may contain local domains in which P and CP symmetries are not preserved. When coupled with an external magnetic field, such P- and CP-odd domains will generate electric currents along the magnetic field --- a phenomenon called the chiral magnetic effect (CME). Recently, the STAR Collaboration at RHIC and the ALICE Collaboration at the LHC released data of charge-dependent azimuthal-angle correlators with features consistent with the CME expectation. However, the experimental observable is contaminated with significant background contributions from elliptic-flow-driven effects, which makes the interpretation of the data ambiguous. In this Letter, we show that the collisions of isobaric nuclei, $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr, provide an ideal tool to disentangle the CME signal from the background effects. Our simulation demonstrates that the two collision types at $\sqrt{s_{\rm NN}}=200$ GeV have more than $10\%$ difference in the CME signal and less than $2\%$ difference in the elliptic-flow-driven backgrounds for the centrality range of $20-60\%$.