The pion pole in hard exclusive vector-meson leptoproduction

Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of rho(0), phi and pi(+) mesons, we investigate the omega spin density matrix elements (SDMEs) recently measured by the HERMES Collaboration. It turns out, from our study, that the pion pole is an important contribution to omega production. It will be treated as a one-particle exchange since its evaluation from the GPD (E) over tilde considerably underestimates its contribution. As an intermediate step of our analysis, we extract the pi omega transition form factor for photon virtualities less than 4 GeV2. From our approach we achieve results for the omega SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive rho(0) and phi leptoproduction is discussed too.