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.
Highlights
Revealing the internal structure of protons and nuclei is one of the central motivations behind the future ElectronIon Collider (EIC) in the US [1,2,3] and similar projects proposed at CERN [4] and in China [5]
We show that electron-photon and electron-vector meson azimuthal angle correlations are sensitive to nontrivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerranVenugopalan initial color charge configurations coupled to the numerical solution of small x JIMWLK evolution equations
These high energy deeply inelastic scattering experiments provide access to hadron and nuclear structure at small Bjorken-x, where nonlinear effects [6,7] tame the growth of gluon densities and generate an emergent semihard scale known as the saturation momentum Qs. The existence of this scale allows for a weak coupling description of the gluon dynamics in this high density regime of quantum chromodynamics (QCD) in a semiclassical effective field theory (EFT) framework known as the color glass condensate (CGC) [8,9,10,11,12,13,14,15,16,17]
Summary
Revealing the internal structure of protons and nuclei is one of the central motivations behind the future ElectronIon Collider (EIC) in the US [1,2,3] and similar projects proposed at CERN [4] and in China [5]. Exclusive photon production, or deeply virtual Compton scattering (DVCS) processes, have been measured at HERA [72,73,74,75] and were shown to be sensitive to the orbital angular momentum of quarks and gluons [25,26,27,76]. We study incoherent diffractive production and demonstrate that at moderate values of jtj the azimuthal correlations are sensitive to event-by-event fluctuations of the spatial gluon distribution in the target. VI and include multiple Appendixes (A–E) that include supplemental details
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