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

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(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(perpendicular to), it will be important to study their feasibility relative to photon-hadron correlations.

Automated summary

The study computes the differential cross-section for inclusive prompt photon+quark production in deeply inelastic scattering of electrons off nuclei at small x, and observes a systematic suppression and broadening pattern of the back-to-back peak in the relative azimuthal angle distribution as the saturation scale is increased. The research also suggests that photon+jet final states at high energies in e + A DIS are a promising channel for exploring gluon saturation that is complementary to inclusive and diffractive dijet production.