Deep electroproduction of photons and mesons on the deuteron

Abstract

Abstract. We study deeply virtual Compton scattering and deep exclusive meson electroproduction on a deuteron target. We model the Generalized Quark Distributions in the deuteron by using the impulse approximation for the lowest Fock-space state on the light-cone. We study the properties of the resulting GPDs, and verify that sum rules violations are quite small in the impulse approximation. Numerical predictions are given for the unpolarized cross sections and polarization asymmetries for the kinematical regimes relevant for JLab experiments and for HERMES at HERA. We conclude that the signal of coherent scattering on the deuteron is comparable to the one on the proton at least for low momentum transfer, providing support to the feasibility of the experiments. The short distance structure of the deuteron may thus be scrutinized in the near future.

Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on an unpolarized deuterium target

“…6 and 7 are theoretical calculations for the incoherent process, based on two different ansätze for modeling GPDs [64] in the VGG model [65] (the coherent process will be considered in Section 6.3.). In this model, a GPD is written as a double distribution [2,3] complemented by a D-term [37,38]: -In the 'factorized ansatz' (VGG Fact. ), the dependences on t and (x, ξ) are uncor- Table 3 Results for azimuthal Fourier amplitudes of the asymmetries with respect to the beam charge and helicity for the exclusive sample.…”

“…Table 5 also includes model predictions from Ref. [38]. This model is based on double distributions, where only the polarizations of the valence quarks are considered for the nucleonic GPDs.…”

“…Since the x dependence of GPDs is thereby only weakly constrained, experimental asymmetries in beam charge must be compared to the predictions of various GPD models. At leading twist (twist-2), the coefficients c [37,38], which contributes only in the 'ERBL' region −ξ < x < ξ where quark GPDs have the characteristics of distribution amplitudes for the creation of a quark-antiquark pair. It does not contribute in the complementary 'DGLAP' region |x| > ξ, where quark GPDs describe the emission and reabsorption of an (anti-)quark in the infinite momentum frame, thereby having properties analogous to the familiar (anti-)quark distribution functions.…”

Angular momentum sum rule for spin-one hadronic systems

“…One can see that the term containing H 2 should dominate the asymmetry, given the expected smallness of H 5 [9,16].…”

Generalized Parton Distributions – theoretical review –

“…Note that the perturbative framework is also applicable for the photon [ 50] and meson [ 51] leptoproduction off nuclei. This opens a new window for the study of nucleus binding effects, especially, for the deuteron [ 10,52].…”