Exclusive vector meson production at HERMES

Hard exclusive production of vector mesons provides access to the unknown generalized parton distributions (GPDs), which give a unified description of the structure of the nucleon. The exclusive electroproduction of rho(0) and phi mesons has been measured on an internal hydrogen gas target at HERMES by using the 27.6 GeV electron (positron) beam of HERA. The cross sections for exclusive rho(0) and phi production have been compared with calculations based on GPD models. For rho(0) production, also the azimuthal single spin asymmetry for a transversely polarized target has been measured. This asymmetry is sensitive to J(q), the quark total angular momentum contribution to the proton spin. Preliminary results are presented and compared to GPD based calculations.