Electroproduction of heavy quarkonia: significance of dipole orientation

Abstract

The differential cross section $d\sigma /d{q}^2$ 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 $\vec{q}$ provides a unique opportunity to identify the reaction plane, due to a strong correlation between the directions of $\vec{q}$ and impact parameter $\vec{b}$. On top of that, the elastic dipole-proton amplitude is subject to a strong correlation between $\vec{b}$ and dipole orientation $\vec{r}$. 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 $\vec{r}$-$\vec{b}$ correlation, which significantly affect the $q$-dependence of the cross section, in particular the ratio of ${\psi }^{\prime }(2S)$ to $J/\psi$ 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.

Comments: 12 pages, 6 figures