Effect of simulating parity-odd observables in high energy heavy ion collisions on Balance Functions of charged particles and elliptic flow of pions

TL;DR

This study investigates how simulating parity-odd effects, specifically charge separation due to the chiral magnetic effect, influences experimental observables like elliptic flow and balance functions in high-energy heavy ion collisions, revealing sensitivity to initial charge separation.

Contribution

The paper introduces a method to incorporate charge separation at the partonic level in AMPT simulations, analyzing its impact on flow and charge correlation observables in heavy ion collisions.

Findings

Balance function shape is sensitive to charge separation.

Pion elliptic flow decreases with increasing charge separation.

Parity observable gamma shows a decreasing trend with charge separation.

Abstract

At the early stage of heavy ion collisions, non-trivial topologies of the gauge fields can be created resulting in an imbalance of axial charge density and eventually separation of electric charges along the direction of the magnetic field produced in such collisions. This process is called the chiral magnetic effect (CME). In this work we implement such a charge separation at the partonic level in AMPT for Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV to study its consequence on experimental observables. We present the effects on the pion elliptic flow ($v_2$) and the charged particle balance function (BF) for varying strengths of initial charge separation. We find that the shape of the balance function is sensitive to the increasing charge separation. $v_2$ of pion shows a strong decreasing trend at higher transverse momenta ($p_T$) with increasing charge separation. Charge balance functions show a peak at $\Delta\phi \sim 180 $ with charge separation implemented in the partonic level as expected for the parity violation. We have also calculated parity observable $\gamma$ in the form of BF's moments. $\gamma$ shows a decreasing trend with charge separation. It has a negative value for charge separation produced by flipping more than 30 $\%$ of quarks in the parton level. We also notice that $<\gamma>$ for the same charge correlation and the opposite charge correlation shows negative and positive values, respectively.