Polarization in diffractive electroproduction of light vector mesons - art. no. 114026

We study in perturbative QCD the helicity amplitudes of the process gamma*p --> rho p at large virtualities Q of the photon gamma*. We estimate all sp in-flip amplitudes taking into account an important effect of the scale beh avior of the gluon density. The transition of a transverse virtual photon t o a longitudinal vector meson is not small at typical conditions at the DES Y ep collider HERA. This helicity nonconserving amplitude leads by interfer ence to a measurable effect in the distribution of the angle between the el ectron scattering and the meson production planes. [S0556-2821(98)02523-5].