Search for Chiral Magnetic Effects in High-Energy Nuclear Collisions

TL;DR

This study measures pion elliptic flow and charge separation in high-energy nuclear collisions to investigate the presence of Chiral Magnetic Effects, revealing charge asymmetry dependencies consistent with theoretical predictions.

Contribution

It provides experimental evidence of charge asymmetry effects on pion flow and charge separation across multiple energies, testing predictions of the Chiral Magnetic Wave and Local Parity Violation.

Findings

Elliptic flow of pions varies linearly with charge asymmetry.

Charge separation signals are observed at various collision energies.

Results align with theoretical models of Chiral Magnetic Wave.

Abstract

We present measurements of pion elliptic flow ($v_2$) in Au+Au collisions at $\sNN =$ 200, 62.4, 39, 27 and 19.6 GeV, as a function of event-by-event charge asymmetry ($A_{\pm}$), based on data from the STAR experiment at RHIC. We find that $\pi^-$ ($\pi^+$) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins and for all the beam energies under study. The slope parameter ($r$) from $v_2(A_\pm)$ difference between $\pi^-$ and $\pi^+$ shows a centrality dependency similar with the calculations with Chiral Magnetic Wave. The measurements of charge separation with respect to the reaction plane in search of Local Parity Violation and Chiral Magnetic Effect are also presented for Au+Au collisions at $\sNN =$ 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV, and for U+U collisions at 193 GeV.