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 ($\gamma$), however, have remained inconclusive, because the non-CME background contributions are not well understood. Experimentally, the $\gamma$ correlators have been measured with respect to the second-order ($\Psi_{ 2}$) and the third-order ($\Psi_{ 3}$) symmetry planes, defined as $\gamma_{ 112}$ and $\gamma_{ 123}$, respectively. The expectation was that with a proper normalization, $\gamma_{ 123}$ would provide a data-driven estimate for the background contributions in $\gamma_{ 112}$. In this work, we calculate different harmonics of the $\gamma$ 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 $\gamma_{ 112}$ and $\gamma_{ 123}$, quantified by $\kappa_{ 112}$ and $\kappa_{ 123}$, respectively. Furthermore, we test another correlator, $\gamma_{ 132}$, within AMPT, and discuss the relation between different $\gamma$ correlators.
Categories: hep-ph hep-ex nucl-ex