UPDATE FOR PROPOSAL E12-06-119 Deeply Virtual Compton Scattering with CLAS12 at 11 GeV

Generalized Parton Distributions (GPDs) are physical observables which can provide deep insight about the internal structure of the nucleon. They contain the usual parton distribution functions (PDFs) and elastic form factors (FFs) as limiting cases or sum rules. In addition, GPDs allow to probe the nucleon as a 3-dimensional object, accessing for instance the quark orbital momentum and picturing the nucleon in quantum phase space. Generalized Parton Distributions can be accessed through deep exclusive processes such as Deeply Virtual Compton Scattering (DVCS). Fifteen years ago, Mueller, Ji, Radyushkin and others [1–6] showed that the DVCS reaction γ * p → γp can, in the Bjorken limit, be factorized into a hard scattering kernel and a non-perturbative part, containing information about the electromagnetic structure of the nucleon in terms of four twist-2 chiral-even GPDs These GPDs depend on 4 variables (x, ξ, t; Q 2). x characterizes the average light-cone momentum fraction of the struck quark in the loop (not directly accessible experimentally). ξ is the longitudinal momentum fraction of the transfer to the proton ∆ = p − p ′ (where p and p ′ are the initial and recoil proton 4-vectors). Finally, t = ∆ 2 is the standard Mandel-stam variable representing the momentum transfer between the virtual and real photons (or between the target and the recoil proton). The scale evolution of the GPDs (Q 2-dependence) has been worked out to next-to-leading order of α S and beyond [7, 8].