Wave function corrections and off-forward gluon distributions in diffractiveJ/ψelectroproduction

Diffractive production of $J/\psi$ particles by virtual photons on a proton target is studied with a view towards understanding two important corrections to the leading order result. First, the effect of Fermi motion of the heavy quarks is studied by performing a systematic expansion in the relative velocity, and a simple correction factor is derived. This is considerably less than estimated previously. Second, since the kinematics necessarily requires that nonzero momentum be transferred to the proton, off-forward gluon distributions are probed by the scattering process. To estimate the importance of the off-forwardness, we compute, in leading order perturbation theory, the extent of deviation from the usual forward gluon distribution in a quark.