Inclusive prompt photon-jet correlations as a probe of gluon saturation in electron-nucleus scattering at small $x$

TL;DR

This paper calculates the cross-section for prompt photon and quark production in electron-nucleus deep inelastic scattering at small x using the Color Glass Condensate framework, exploring gluon saturation effects at the EIC.

Contribution

It provides the first detailed computation of inclusive prompt photon+quark production in e+A DIS within the CGC framework, highlighting its potential to probe gluon saturation.

Findings

Back-to-back azimuthal correlations are suppressed and broadened with increasing saturation scale.

Photon+jet correlations are sensitive to gluon saturation effects at the EIC.

Results support photon+jet as a promising channel for studying gluon saturation.

Abstract

We compute the differential cross-section for inclusive prompt photon$+$quark production in deeply inelastic scattering of electrons off nuclei at small $x$ ($e+A$ DIS) in the framework of the Color Glass Condensate effective field theory. The result is expressed as a convolution of the leading order (in the strong coupling $\alpha_{\mathrm{s}}$) impact factor for the process and universal dipole matrix elements, in the limit of hard photon transverse momentum relative to the nuclear saturation scale $Q_{s,A}(x)$. We perform a numerical study of this process for the kinematics of the Electron-Ion Collider (EIC), exploring in particular the azimuthal angle correlations between the final state photon and quark. We observe a systematic suppression and broadening pattern of the back-to-back peak in the relative azimuthal angle distribution, as the saturation scale is increased by replacing proton targets with gold nuclei. Our results suggest that photon+jet final states in inclusive $e+A$ DIS at high energies are in general a promising channel for exploring gluon saturation that is complementary to inclusive and diffractive dijet production. They also provide a sensitive empirical test of the universality of dipole matrix elements when compared to identical measurements in proton-nucleus collisions. However because photon+jet correlations at small $x$ in EIC kinematics require jet reconstruction at small $k_\perp$, it will be important to study their feasibility relative to photon-hadron correlations.