Abstract
We have studied in perturbative QCD all independent helicity amplitudes describing the photoproduction of Light vector mesons at large t. We found a new hard production mechanism which is related to the possibility for a real photon to fluctuate into a massless q (q) over bar pair in a chiral-odd spin configuration. Each helicity amplitude is given as a sum of a usual chiral-even contribution ...
Abstract
We have studied in perturbative QCD all independent helicity amplitudes describing the photoproduction of Light vector mesons at large t. We found a new hard production mechanism which is related to the possibility for a real photon to fluctuate into a massless q (q) over bar pair in a chiral-odd spin configuration. Each helicity amplitude is given as a sum of a usual chiral-even contribution (when the helicities of quark and antiquark are antiparallel) and this additional chiral-odd part (where the helicities of quark and antiquark are parallel). The chiral-odd contribution is large, it leads to a dominance of the non spin-flip amplitude in a very broad region of intermediately high 
All amplitudes are expressed in terms of short distance asymptotics of the light-cone wave functions of vector meson (photon). We demonstrate that for each helicity amplitude there exists a soft non-factorizable contribution, We give arguments that for dominant non spin-flip helicity amplitude the relative contribution of the soft nonfactorizable interactions is numerically not large. (C) 2000 Elsevier Science B,V. All rights reserved.
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