The exclusive diffractive production of light vector mesons (ρ~0 and Φ) in the intermediate energy region at moderate Q~2 is described. Double-spin asymmetries in the cross section for ρ~0 and Φ 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 ρ~0 and Φ 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.
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