Chiral kinetic approach to the chiral magnetic effect in isobaric collisions

TL;DR

This study uses a chiral kinetic approach with initial conditions from a multiphase transport model to investigate the chiral magnetic effect in isobaric collisions, highlighting the importance of the reaction plane and the robustness of certain observables.

Contribution

It introduces a detailed analysis of the chiral magnetic effect in isobaric collisions using a chiral kinetic model with specific focus on observable differences based on reaction and event plane definitions.

Findings

A measurable difference in the $ ext{γ}^{OS}- ext{γ}^{SS}$ observable between Zr+Zr and Ru+Ru collisions when using the reaction plane.

The $ ext{γ}^{OS}- ext{γ}^{SS}$ signal diminishes and becomes comparable to background when using the event plane.

The $R( ext{Δ}S)$ correlator shows less dependence on plane choice, making it a more robust observable for the chiral magnetic effect.

Abstract

Based on the chiral kinetic approach using quarks and antiquarks from a multiphase transport model as initial conditions, we study the chiral magnetic effect, i.e., the magnetic field induced separation of charged particles in the transverse plane, in non-central isobaric collisions of Zr$+$Zr and Ru$+$Ru, which have the same atomic number but different proton numbers. For the observable $\gamma^{OS}-\gamma^{SS}$ related to the difference between the correlations of particles of opposite charges and of same charges, we find a difference between the two collision systems if the magnetic field has a long lifetime of 0.6 fm$/c$ and the observable is evaluated using the initial reaction plane. This signal of the chiral magnetic effect becomes smaller and comparable to the background contributions from elliptic flow if the event plane determined from particle emission angles is used. For the other observable given by the $R(\Delta S)$ correlator related to the distribution of average charge separation in a collision, the signal due to the chiral magnetic effect is found to depend less on whether the reaction or event plane is used in the analysis, and their difference between the two isobaric collision systems is thus a more robust observable.