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 (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.