From hard exclusive meson electroproduction to deeply virtual Compton scattering

We systematically evaluate observables for hard exclusive electroproduction of real photons and compare them to experiment using a set of Generalized Parton Distributions (GPDs) whose parameters are constrained by Deeply Virtual Meson Production data, nucleon form factors and parton distributions. The Deeply Virtual Compton Scattering amplitudes are calculated to leading-twist accuracy and leading order in QCD perturbation theory while the leptonic tensor is treated exactly, without any approximation. This study constitutes a check of the universality of the GPDs. We summarize all relevant details on the parametrizations of the GPDs and describe its use in the handbag approach of the aforementioned hard scattering processes. We observe a good agreement between predictions and measurements of deeply virtual Compton scattering on a wide kinematic range, including most data from H1, ZEUS, HERMES, Hall A and CLAS collaborations for unpolarized and polarized targets when available. We also give predictions relevant for future experiments at COMPASS and JLab after the 12 GeV upgrade.Comment: 37 pages, 12 figures v2 : fixed typos, updated to future published version (EPJC). v3 : fixed typo in Eq. (59

Spin and other aspects of generalized parton distributions

I discuss how generalized parton distribution probe various aspects of QCD bound states. Topics include the interplay between transverse and longitudinal structure, quantum mechanical interference, orbital angular momentum, helicity flip, and higher-spin targets.Comment: 9 pages, 2 figures. Talk given at Pacific Spin 2001, Beijing, China, 8-13 Oct. 200

Concluding remarks on QCD-N'02 Workshop at Ferrara

A summary is given of some important developments in QCD studies of the nucleon as presented at this workshop. Based on these developments some expectations for the short- and long-term future of the field are sketched. Taken together, the summary of the workshop and the future perspectives result in a {\sl Road Map} for experimental studies of the QCD structure of the nucleon. The Road Map includes as a long-term goal the construction of new lepton-hadron scattering facilities both in Europe and the United States.Comment: 10 pages, no figures, contribution to the proceedings of European Workshop on the QCD Structure of the Nucleon, Ferrara, Italy, 3 - 6 April 200

Nucleon hologram with exclusive leptoproduction

Hard exclusive leptoproductions of real photons, lepton pairs and mesons are the most promising tools to unravel the three-dimensional picture of the nucleon, which cannot be deduced from conventional inclusive processes like deeply inelastic scattering.Comment: 9 pages LaTeX, 7 figures, sign in Eq. (16) corrected, Invited talk at the European Workshop "QCD structure of the nucleon", Ferrara, Italy, April 3-6, 200

Elastic meson production and Compton scattering

I discuss recent progress in the theory of exclusive meson production and Compton scattering, focusing on hard-scattering factorization and on the dipole formalism.Comment: 15 pages. Talk given at the Ringberg Workshop on New Trends in HERA Physics 2001. v2: References adde

DVCS on spinless nuclear targets in impulse approximation

Within the impulse approximation, we derive expressions for the amplitude of deeply virtual Compton scattering on spinless nuclei in terms of the generalized parton distributions of the nucleon. As an application, nuclear effects in the beam-charge and single-spin asymmetries are discussed.Comment: 13 pages, 2 figures, Late

Deeply virtual Compton scattering on longitudinally polarized protons and neutrons at CLAS

This paper focuses on a measurement of deeply virtual Compton scattering (DVCS) performed at Jefferson Lab using a nearly-6-GeV polarized electron beam, two longitudinally polarized (via DNP) solid targets of protons (NH3) and deuterons (ND3) and the CEBAF Large Acceptance Spectrometer. Here, preliminary results for target-spin asymmetries and double (beam-target) asymmetries for proton DVCS, as well as a very preliminary extraction of beam-spin asymmetry for neutron DVCS, are presented and linked to Generalized Parton Distributions.Comment: 6 pages, 5 figures. Proceedings for the QNP2012 conferenc