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 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. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 667–673 (10 November 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.