# Disentangling flow and signals of Chiral Magnetic Effect in U+U, Au+Au and p+Au collisions

## TL;DR

This paper measures charge-dependent correlations in heavy-ion and proton-nucleus collisions to disentangle signals of the Chiral Magnetic Effect from background effects, providing insights into the underlying physics of charge separation phenomena.

## Contribution

It introduces a differential measurement of the charge-dependent correlator with pseudorapidity separation to distinguish CME signals from flow-related backgrounds in various collision systems.

## Key findings

- Charge separation observed, but largely explained by background effects.
- Short-range correlations dominate in peripheral A+A and p+A collisions.
- Wider correlations tend to vanish similarly to magnetic field projections.

## Abstract

We present STAR measurements of the charge-dependent three-particle correlator $\gamma^{a,b}=\langle \cos(\phi_1^{a}+\phi_2^{b}-2\phi_3)\rangle/v_{2}\{2\}$ and elliptic flow $v_{2}\{2\}$ in U+U, Au+Au and p+Au collisions at RHIC. The difference $\Delta \gamma = \gamma(\rm{opposite\!-\!sign})\!-\!\gamma(\rm{same\!-\!sign})$ measures charge separation across the reaction plane, a predicted signal of the Chiral Magnetic Effect (CME). Although charge separation has been observed, it has been argued that the measured separation can also be explained by elliptic flow related backgrounds. In order to separate the two effects, we perform measurements of the $\gamma$-correlator where background expectations differ from magnetic field driven effects. A differential measurement of $\gamma$ with the relative pseudorapidity ($\Delta\eta$) between the first and second particles indicate that $\Delta \gamma$ in peripheral A+A and p+A collisions are dominated by short-range correlations in $\Delta\eta$. However, a relatively wider component of the correlation in $\Delta\eta$ tends to vanish the same way as projected magnetic field as predicted by MC-Glauber simulations.