Momentum transfer dependence in electronuclear production of heavy quarkonia revisited: Green's function formalism

Abstract

Momentum transfer distributions $d\sigma/dt$ in diffractive 
electroproduction of heavy quarkonia on nuclear targets are 
studied within a rigorous quantum-mechanical approach based 
on the light-front Green's function formalism. Such a formalism allows to include naturally the higher-twist and leading-twist shadowing corrections, as well as the color transparency effects. Model calculations of $d\sigma/dt$, containing also the correlation between impact parameter of a collision $\vec{b}$ and dipole orientation $\vec{r}$, are tested by the recent data on charmonium production in ultra-peripheral nuclear collisions on proton and lead target. In model predictions on nuclear target, the reduced quark shadowing leads to a significant decrease in $d\sigma/dt$ in kinematic regions scanned by experiments at the prepared electron-ion collider at Brookhaven National Laboratory. At high energies, relevant to current Large-Hadron-Collider and future Large-Hadron-Electron-Collider experiments, the gluon shadowing causes a non-monotonic energy dependence of $d\sigma/dt$ which may indicate possible onset of gluon saturation effects.