Abstract
We study the exclusive electroproduction of a photon pair in the kinematical regime where the diphoton invariant mass is large and where the nucleon flies almost in its original direction. We discuss the relative importance of the QCD process where the two photons originate from a quark line compared to the single (double) Bethe-Heitler processes where one (two) photons originate from the lepton line. This process turns out to be a promising tool to study generalized parton distributions in the nucleon, both at the medium energy of JLab and at a high energy electron ion collider.
Highlights
Hard electroproduction processes are a powerful probe of the hadronic structure
Our calculation of the leading order leading twist amplitude of reaction (2) has demonstrated that the electroproduction of a large invariant mass diphoton is an interesting process to analyze in the collinear factorization framework, both at current experimental facilities such as JLab and Compass at CERN, and in future high energy experiments
Let us remind the reader that the main conclusion of this study is that the amplitude only depends on C-odd generalized parton distributions (GPDs) at the border values x 1⁄4 Æξ. (ii) On the other hand, the single Bethe-Heitler process strongly dominates the amplitude in the domain where Q2 is not extremely small, especially in the large energy domain of the electron-ion collider (EIC)
Summary
Hard electroproduction processes are a powerful probe of the hadronic structure. Their understanding in the framework of the QCD collinear factorization of hard amplitudes in specific kinematics in terms of generalized parton distributions (GPDs) and hard perturbatively calculable coefficient functions [1,2] offers a way to access the inner structure of nucleons and light nuclei. In a previous work [3,4], we studied the exclusive photoproduction of two photons on an unpolarized proton or neutron target, γðq; εÞ þ NðP1; s1Þ → γðk; ε1Þ þ γðk; ε2Þ þ N0ðP2; s2Þ; ð1Þ in the kinematical regime of large invariant diphoton squared mass M2γγ 1⁄4 ðk þ k2Þ2 of the final photon pair and small momentum transfer t 1⁄4 ðP2 − P1Þ2 between the initial and the final nucleons. This process shares many features with timelike Compton scattering (TCS), the photoproduction of a large mass lepton pair [5]. We present the spinor techniques used in our calculations
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