Extraction of the Compton Form Factor H from DVCS Measurements in the Quark Sector

Working at twist 2 accuracy and assuming the dominance of the Generalized Parton Distribution H we study the helicity-dependent and independent cross sections measured in Hall A, the beam spin asymmetries measured in Hall B at Jefferson Laboratory and beam charge, beam spin and target spin asymmetries measured by Hermes. We extract the real and imaginary parts of the Compton Form Factor H, the latter being obtained with a 20--50% uncertainty. We pay extra attention to the estimation of systematic errors on the extraction of H. We discuss our results and compare to other extractions as well as to the popular VGG model.Comment: 6 pages, 3 figures, Plenary talk given at the 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2010), Williamsburg, Virginia, USA, 31 May - 4 Jun 201

Pion's valence-quark GPD and its extension beyond DGLAP region

We briefly report on a recent computation, with the help of a fruitful algebraic model, sketching the pion valence dressed-quark generalized parton distribution and, very preliminary, discuss on a possible avenue to get reliable results in both Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and Efremov-Radyushkin-Brodsky-Lepage (ERBL) kinematial regions.Comment: 6 pages, 4 figures, contribution to 21st International conference on Few-Body Problem

On timelike and spacelike deeply virtual Compton scattering at next to leading order

We study timelike and spacelike virtual Compton scattering in the generalized Bjorken scaling regime at next to leading order in the strong coupling constant, in the medium energy range which will be studied intensely at JLab12 and in the COMPASS-II experiment at CERN. We show that the Born amplitudes get sizeable O(\alpha_s) corrections and, even at moderate energies, the gluonic contributions are by no means negligible. We stress that the timelike and spacelike cases are complementary and that their difference deserves much special attention

Timelike vs spacelike DVCS from JLab, Compass to ultraperipheral collisions and AFTER@LHC

Timelike and spacelike virtual Compton scattering in the generalized Bjorken scaling regime are complementary tools to access generalized parton distributions. We stress that the gluonic contributions are by no means negligible, even in the medium energy range which will be studied intensely at JLab12 and in the COMPASS-II experiment at CERN. Ultraperipheral collisions with proton or ion beams may also be used at RHIC and at collider or fixed target experiments at LHC.Comment: 7 pages, Presented at the Low x workshop, May 30 - June 4 2013, Rehovot and Eilat, Israe

Spacelike and Timelike Compton Scattering: Progress report

We present some recent results on the analysis of hard scattering processes in the framework of Generalized Parton Distributions. In particular we compute DVCS observables on unpolarized targets with the Kroll - Goloskokov model (suited to DVMP analysis). We also discuss NLO contributions to DVCS and TCS processes for various kinematic settings.Comment: To appear in the proceedings of the 20th International Workshop on Deep-Inelastic Scattering and Related Subjects held in Bonn (March 26 - 30, 2012

Extraction of the Compton Form Factor H from DVCS measurements at Jefferson Lab

In the framework of Generalised Parton Distributions, we study the helicity-dependent and independent cross sections measured in Hall A and the beam spin asymmetries measured in Hall B at Jefferson Laboratory. We perform a global fit of these data and fits on each kinematical bin. We extract the real and imaginary parts of the Compton Form Factor $\mathcal{H}$ under the main hypothesis of dominance of the Generalised Parton Distribution $H$ and twist 2 accuracy. We discuss our results and compare to previous extractions as well as to the VGG model. We pay extra attention to the estimation of errors on the extraction of $\mathcal{H}$.Comment: 24 pages, 8 figure

NLO QCD corrections for DVCS and TCS

The inclusion of QCD corrections to the Born amplitude of deeply virtual Compton scattering in both spacelike (DVCS) and timelike (TCS) regimes modifies the extraction process of generalized parton distributions (GPDs) from observables. In particular, gluon contributions are by no means negligible even in the medium energy range accessible at JLab12. We emphasize the complementarity of spacelike and timelike measurements and raise the question of factorization scale dependence of the O(alpha_S) results.Comment: 6 pages, 6 figures, Proceedings of the conference Photon 2013, 20-24 May 2013 Paris, France, to be published in Proceedings of Scienc