Gluon imaging using azimuthal correlations in diffractive scattering at the Electron-Ion Collider

TL;DR

This paper investigates how azimuthal correlations in diffractive scattering at the Electron-Ion Collider reveal spatial and fluctuation patterns in the gluon distribution of protons and nuclei, using the Color Glass Condensate framework.

Contribution

It introduces a detailed theoretical study of azimuthal correlations in diffractive scattering, incorporating spatially dependent initial conditions and small x evolution, to probe gluon spatial correlations.

Findings

Significant azimuthal anisotropies in electron-proton collisions ($v_{1,2} ext{ approx } 2-10 ext{%}$).

Much smaller azimuthal modulations in electron-gold collisions ($v_{1,2} <0.1 ext{%}$).

Azimuthal correlations are sensitive to gluon distribution fluctuations in the target.

Abstract

We study coherent diffractive photon and vector meson production in electron-proton and electron-nucleus collisions within the Color Glass Condensate effective field theory. We show that electron-photon and electron-vector meson azimuthal angle correlations are sensitive to non-trivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerran-Venugopalan initial color charge configurations coupled to the numerical solution of small $x$ JIMWLK evolution equations. We compute the cross-section differentially in $Q^2$ and $|t|$ and find sizeable anisotropies in the electron-photon and electron-$\mathrm{J}/\psi$ azimuthal correlations ($v_{1,2} \approx 2 - 10 \%$) in electron-proton collisions for the kinematics of the future Electron-Ion Collider. In electron-gold collisions these modulations are found to be significantly smaller ($v_{1,2} <0.1 \%$). We also compute incoherent diffractive production where we find that the azimuthal correlations are sensitive to fluctuations of the gluon distribution in the target.