Constraints on the H~\tilde{H} Generalized Parton Distribution from Deep Virtual Compton Scattering Measured at HERMES

We have analyzed the longitudinally polarized proton target asymmetry data of the Deep Virtual Compton process recently published by the HERMES collaboration in terms of Generalized Parton Distributions. We have fitted these new data in a largely model-independent fashion and the procedure results in numerical constraints on the $\tilde{H}_\mathrm{Im}$ Compton Form Factor. We present its $t-$ and $\xi-$ dependencies. We also find improvement on the determination of two other Compton Form Factors, $H_\mathrm{Re}$ and $H_\mathrm{Im}$.Comment: 14 pages, 5 figure

Generalized Parton Distributions : Experimental aspects

After briefly outlining the formalism of the Generalized Parton Distributions (GPDs) in the first sections, we discuss some general considerations for their experimental study : in particular, the relation between GPDs and experimental observables and the need and requirements for a dedicated experimental facility. Also, we review and comment the first experimental signatures of this physics recently observed by the HERMES and CLAS (at JLab) collaborations.Comment: 10 pages, Invited talk at ICTP 3rd International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 7-11 May 2001. Submitted to Nucl.Phys.

Deeply Virtual Electroproduction of Photons and Mesons

In this paper, after a brief summary of the properties of the Off-Forward Parton Distributions, we give some examples of what could be the experimental opportunities to access them at the current high-energy lepton facilities : JLab (E_e >= 6 GeV), HERMES (E_e = 27 GeV) and COMPASS (E_mu = 200 GeV).Comment: 5 pages, 3 figure

Generalized Parton Distributions from Deep Virtual Compton Scattering at CLAS

We have analyzed the beam spin asymmetry and the longitudinally polarized target spin asymmetry of the Deep Virtual Compton Scattering process, recently measured by the Jefferson Lab CLAS collaboration. Our aim is to extract information about the Generalized Parton Distributions of the proton. By fitting these data, in a largely model-independent procedure, we are able to extract numerical values for the two Compton Form Factors $H_{Im}$ and $\tilde{H}_{Im}$ with uncertainties, in average, of the order of 30%.Comment: 9 pages, 5 figure

Electroproduction of strangeness above the resonance region

A simple and elegant model, based on Reggeized t-channel exchanges is succesful in reproducing the main features of all existing data of the reactions ep->eKLambda and ep->eKSigma. In particular, the original way gauge invariance is taken into account is found to be essential to describe the ratio between the Coulomb and the Transverse cross-sections at large Q2 that has been measured recently at JLab.Comment: 5 pages, 5 figures, submitted to Phys.Rev.Let

Role of nucleon resonance excitation in ϕ\phi meson photoproduction

The resonance effects are investigated in the $\phi$ meson photoproduction near threshold through a quark model approach with an effective Lagrangian. The diffractive contribution is consistently estimated by the {\it t}-channel Pomeron exchange. Another non-diffractive process, {\it t}-channel $\pi^0$ exchange is also included. The numerical result shows that the Pomeron exchange plays dominant role in the $\phi$ meson photoproduction, while the cross sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel excitations, and {\it t}-channel $\pi^0$ exchange, are quite small. In the polarization observables, we find that large asymmetries are produced in the backward direction by the interferences from the {\it s}- and {\it u}-channel resonances, while in the forward direction, only very small asymmetries are generated. Meanwhile, we find that the effects from the $\pi^0$ exchange are generally negligible.Comment: Contribution to "2nd International Conference on Perspectives in Hadronic Physics", Trieste, ICTP, 10-14 May 1999, to appear in Few-body Syste

Exclusive rho^0 electroproduction on the proton : GPDs or not GPDs ?

We discuss the interpretation of the $ep\to ep\rho^0$ process in terms of, on the one hand, Generalized Parton Distributions and, on the other hand, an effective hadronic model based on Regge theory.Comment: 11 pages, 4 figures, proceedings of the workshop on "Exclusive Reactions at High Momentum Transfer", Jefferson Lab, May0

Exclusive electromagnetic production of strangeness on the nucleon : review of recent data in a Regge approach

In view of the numerous experimental results recently released, we provide in this letter an update on the performance of our simple Regge model for strangeness electroproduction on the nucleon. Without refitting any parameters, a decent description of all measured observables and channels is achieved. We also give predictions for spin transfer observables, recently measured at Jefferson Lab which have high sensitivity to discriminate between different theoretical approaches.Comment: 5 pages, 5 figure

K+ photoproduction at SPring-8/LEPS

A series of experiments have been carried out by using a linearly polarized photon beam at the SPring-8/LEPS facility from December 2000 to June 2001. The photon beam asymmetries and differential cross sections of the p(gamma,K+)Lambda and p(gamma,K+)Sigma^0 reactions have been measured in the photon energy range from 1.5 GeV to 2.4 GeV at forward angles, 0 deg. < Theta_cm < 60 deg.. We report preliminary results of the photon beam asymmetries.Comment: 4 pages, 4 figures, to be published in the Proceedings (Nuclear Physics A) of the PANIC02, Osaka, Sept 30 - Oct 4, 200

A fitter code for Deep Virtual Compton Scattering and Generalized Parton Distributions

We have developped a fitting code based on the leading-twist handbag Deep Virtual Compton Scattering (DVCS) amplitude in order to extract the Generalized Parton Distributions (GPD) information from DVCS observables in the valence region. In a first stage, with simulations and pseudo-data, we show that the full GPD information can be recovered from experimental data if enough observables are measured. If only part of these observables are measured, valuable information can still be extracted, certain observables being particularly sensitive to certain GPDs. In a second stage, we make a practical application of this code to the recent DVCS Jefferson Lab Hall A data from which we can extract numerical constraints for the two $H$ GPD Compton Form Factors.Comment: 15 pages, 8 figure