Cumulant Expansion in Gluon Saturation, and Five and Six-Gluon Azimuthal Correlations

TL;DR

This paper develops a cumulant expansion framework for five- and six-gluon correlations within saturation physics, providing new tools to analyze multi-gluon correlations and flow coefficients in high-energy collisions.

Contribution

It introduces a novel cumulant expansion for gluon correlators in saturation physics and applies superdiagrams to compute higher-order gluon correlations.

Findings

Derived the cumulant expansion valid in the gluon saturation limit.

Calculated five- and six-gluon correlation functions using superdiagrams.

Provided insights into extracting flow coefficients from multi-gluon correlations.

Abstract

Correlations between the momenta of the final state hadrons measured in proton or nucleus collisions contain information that sheds light on the initial conditions and evolutionary dynamics of the collision system. These correlation measurements have revealed the long-range rapidity correlations in p-p and p-Pb systems, and they have also made it possible to extract the elliptic flow coefficient from hadron correlation measurements. In this work, we calculate five- and six-gluon correlation functions in the framework of saturation physics by using superdiagrams. We also derive the cumulant expansion of the gluon correlators that is valid in the gluon saturation limit. We show that the cumulant expansion of the gluon correlators that is used for counting the number of diagrams to be calculated does not follow the standard cumulant expansion. We also explain how these findings can be used in obtaining experimentally relevant observables such as flow coefficients calculated from correlations as well as ratios of the correlation functions of different orders.