Diffractive vector mesons beyond the s-channel helicity conservation

Abstract
We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of light to heavy vector mesons in deep inelastic scattering. For large Q 2 all helicity amplitudes but the double-flip are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar hardness scale. We find a substantial breaking of the s-channel helicity conservation, which must persist in real photoproduction also.