Diffractive vector mesons beyond the s-channel helicity conservation

We derive a full set, and determine the twist, of helicity amplitudes for diffractive production of vector mesons in deep inelastic scattering. We show that for large $Q^{2}$ all helicity amplitudes are calculable in perturbative QCD and are proportional to the gluon structure function of the proton at a similar pQCD hardness scale. We find a substantial breaking of the $s$-channel helicity conservation which must persist also in real photoproduction.