# Initial state qqg correlations as a background for the Chiral Magnetic Effect in collision of small systems

## TL;DR

This paper calculates initial state three-particle correlations in proton-nucleus collisions within the Color Glass Condensate framework to understand background signals for the Chiral Magnetic Effect, revealing rapidity-dependent effects that could influence experimental observations.

## Contribution

It provides the first calculation of three-particle correlations involving two quarks and one gluon in the initial state, highlighting rapidity dependence and potential impact on CME background understanding.

## Key findings

- Two distinct contributions to correlations: rapidity-independent and rapidity-dependent.
- Rapidity-dependent contribution leads to negative same-charge correlations at large rapidity separation.
- Initial state correlations may partially explain experimental CME signals.

## Abstract

Motivated by understanding the background to Chiral Magnetic Effect in proton-nucleus collisions from first principles, we compute the three particle correlation in the projectile wave function. We extract the correlations between two quarks and one gluon in the framework of the Color Glass Condensate. This is related to the same-charge correlation of the conventional observable for the Chiral Magnetic Effect. We show that there are two different contributions to this correlation function. One contribution is rapidity-independent and as such can be identified with the pedestal; while the other displays rather strong rapidity dependence. The pedestal contribution and the rapidity-dependent contribution at large rapidity separation between the two quarks result in the negative same charge correlations, while at small rapidity separation the second contribution changes sign. We argue that the computed initial state correlations might be partially responsible for the experimentally observed signal in proton-nucleus collisions.