Spin physics of vector meson production at HERMES

The exclusive diffractive production of light vector mesons (rho(0) and phi) in the intermediate energy region at moderate Q(2) is described. Double-spin asymmetries in the cross section for rho(0) and phi mesons have been measured in electroproduction and quasi-real photoproduction on proton and deuterium targets. Moreover, spin density matrix elements have been determined for exclusive diffractive rho(0) and phi production, which are compared to results obtained at higher energy. From these data the helicity transfer from the virtual photon to the vector mesons, the ratio of the longitudinal to transverse components of the production cross section, and a test of the s-channel helicity conservation have been obtained.