Diffractive vector mesons beyond the s-channel helicity conservation
Kuraev E.V., Nikolaev N.N., Zakharov B.G.
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 Q2 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 hard scale. We find a substantial breaking of the я-channel helicity conservation which must persist also in real photoproduction.