Deeply virtual and exclusive electroproduction of ω-mesons

The exclusive $\omega$ 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 GeV$^2$) 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 $\omega$ 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 $\gamma^*p \to \omega p$, even for Q$^2$ as large as 5 GeV$^2$. 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.