Background evaluations for the chiral magnetic effect with normalized correlators using a multiphase transport model

Abstract

The chiral magnetic effect (CME) induces an electric charge separation in a chiral medium along the magnetic field that is mostly produced by spectator protons in heavy-ion collisions. The experimental searches for the CME, based on the charge-dependent angular correlations (${\hat{I}}^3$), however, have remained inconclusive, because the non-CME background contributions are not well understood. Experimentally, the ${\hat{I}}^3$ correlators have been measured with respect to the second-order ($\hat{I}{¨}_2$) and the third-order ($\hat{I}{¨}_3$) symmetry planes, defined as ${\hat{I}}_{112}^3$ and ${\hat{I}}_{123}^3$, respectively. The expectation was that with a proper normalization, ${\hat{I}}_{123}^3$ would provide a data-driven estimate for the background contributions in ${\hat{I}}_{112}^3$. In this work, we calculate different harmonics of the ${\hat{I}}^3$ correlators using a charge-conserving version of a multiphase transport (AMPT) model to examine the validity of the said assumption. We find that the pure-background AMPT simulations do not yield an equality in the normalized ${\hat{I}}_{112}^3$ and ${\hat{I}}_{123}^3$, quantified by $\hat{I}{º}_{112}$ and $\hat{I}{º}_{123}$, respectively. Furthermore, we test another correlator, ${\hat{I}}_{132}^3$, within AMPT, and discuss the relation between different ${\hat{I}}^3$ correlators.

8 pages, 6 figures