A novel invariant mass method to isolate resonance backgrounds from the chiral magnetic effect

Abstract

The Chiral Magnetic Effect (CME) refers to charge separation along a strong magnetic field, due to topological charge fluctuations in QCD. Charge correlation ($\hat{I}”{\hat{I}}^3$) signals consistent with CME have been first observed almost a decade ago. It has also been known since then that the $\hat{I}”{\hat{I}}^3$ is contaminated by a major background from resonance decays coupled with elliptic flow. In this contribution, we propose differential $\hat{I}”{\hat{I}}^3$ measurements as function of the pair invariant mass ($m_{\mathrm{inv}}$). The $\hat{I}”{\hat{I}}^3$ in the high $m_{\mathrm{inv}}$ region is essentially free of resonance backgrounds. In the low $m_{\mathrm{inv}}$ region, the $\hat{I}”{\hat{I}}^3$ backgrounds show resonance peaks. The CME signal, presumably smooth in $m_{\mathrm{inv}}$, may thus be extracted from a two-component model fit. We demonstrate the feasibility and effectiveness of this novel method by using the AMPT and toy-model Monte-Carlo simulations. We also discuss an application of the method in data analysis.

4 pages 4 figures. Quark Matter 2018 proceedings