Exclusive electroproduction of vector and pseudoscalar mesons at HERMES

The exclusive production of vector and pseudoscalar mesons in deep-inelastic lepton scattering gives a mean to access the recently introduced generalized parton distributions (GPDs). The GPDs provide a unified description of hadronic structure, which can be investigated with many different reactions. Recent results are presented on the exclusive electroproduction of pi(+) mesons and on diffractive rho(0) and phi production on the proton, collected by the HERMES collaboration at DESY. The experimental results for the rho(0) and phi cross section are compared to calculations based on a description of the reactions in terms of GPDs. It is shown that quark exchange is the dominant production mechanism for rho(0) production, while for phi production only gluon exchanges contributes. For exclusively produced pi(+), an asymmetry in the azimuthal distribution around the virtual photon direction has been observed which depends on the orientation of the target spin.