Deeply Virtual and Exclusive Electroproduction of Mesons

The exclusive w electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q(2)) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross-sections were measured up to large values of the four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the interference terms sigma(TT) and sigma(TL) to the cross-sections, as well as an analysis of the w spin density matrix, indicate that helicity is not conserved in this process. The t-channel pi(0) exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction gamma*p -> wp, even for Q(2) as large as 5 GeV2. Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross-sections is nearly Q(2)-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.