Realistic implementation of chiral magnetic wave in heavy ion collisions

Abstract

A chiral magnetic wave (CMW) is a gapless collective excitation of chiral charges along the direction of magnetic field in the quark-gluon plasma that arises from the triangle anomaly of QCD. We perform a reliable study of the CMW in a realistic simulation of heavy ion collisions, and find that the CMW contributions to the charge-dependent elliptic flow of pions, $\ensuremath{\Delta}{v}_{2}\ensuremath{\equiv}{v}_{2}({\ensuremath{\pi}}^{\ensuremath{-}})\ensuremath{-}{v}_{2}({\ensuremath{\pi}}^{+})$, linearly depending on the net charge asymmetry ${A}_{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\equiv}({N}_{+}\ensuremath{-}{N}_{\ensuremath{-}})/({N}_{+}+{N}_{\ensuremath{-}})$ with a positive slope $r$, is comparable to the recent experimental results from the Relativistic Heavy Ion Collider (RHIC). We identify a ``freeze-out hole effect,'' which is a direct consequence of the propagation of the CMW during the realistic evolution of the fireball, as the dominant physics effect responsible for a sizable contribution from the CMW to the slope parameter $r$, and emphasize that a proper treatment of the freeze-out condition is crucial in any reliable computation of the CMW contribution to the slope parameter $r$. We also implement a chiral phase transition effect in our study, which illustrates the sensitivity of the results to chiral phase transition temperature, and suggest that the CMW can be an important probe of the QCD chiral phase transition. Our results on the impact parameter dependence compare well with the RHIC experiments. We also give predictions for the Large Hadron Collider (LHC) energy.