Electroproduction of heavy quarkonia: Significance of dipole orientation

The differential cross section dσ/dq² of diffractive electroproduction of heavy quarkonia on protons is a sensitive study tool for the interaction dynamics within the dipole representation. Knowledge of the transverse momentum transfer →q provides a unique opportunity to identify the reaction plane, due to a strong correlation between the directions of →q and impact parameter →b. On top of that, the elastic dipole-proton amplitude is subject to a strong correlation between →b and dipole orientation →r. Most of models for b-dependent dipole cross sections either completely miss this information, or make unjustified assumptions. We perform calculations basing on a realistic model for →r-→b correlation, which significantly affect the q dependence of the cross section, in particular the ratio of ψ^'(2S) to J/ψ(1S) yields. We rely on realistic potential models for the heavy quarkonium wave function and the Lorentz-boosted Schr\"odinger equation.