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 q⃗ provides a unique opportunity to identify the reaction plane, due to a strong correlation between the directions of q⃗ and impact parameter b⃗ . On top of that, the elastic dipole-proton amplitude is subject to a strong correlation between b⃗ and dipole orientation r⃗ . Most of models for b-dependent dipole cross section either completely miss this information, or make unjustified assumptions. We perform calculations basing on a realistic model for r⃗ -b⃗ correlation, which significantly affect the q-dependence of the cross section, in particular the ratio of ψ′(2S) to J/ψ yields. We rely on realistic potential models for the heavy quarkonium wave function, and the Lorentz-boosted Schrödinger equation. Good agreement with data on q-dependent diffractive electroproduction of heavy quarkonia is achieved.