Transverse Single Spin Asymmetry in $e+p^\uparrow \to e+J/\psi +X $ and Transverse Momentum Dependent Evolution of the Sivers Function

TL;DR

This paper investigates the transverse single spin asymmetry in J/psi electroproduction, incorporating the scale evolution of TMD parton distributions and gluon Sivers function, revealing a reduction in asymmetry compared to previous models.

Contribution

It introduces the first analysis of TMD evolution effects on SSA in J/psi production across multiple experimental energies.

Findings

SSA is reduced when TMD evolution is included.

The analysis covers JLab, HERMES, COMPASS, and eRHIC energies.

TMD evolution impacts the predicted asymmetries significantly.

Abstract

We extend our analysis of transverse single spin asymmetry (SSA) in electroproduction of $J/\psi$ to include the effect of the scale evolution of the transverse momentum dependent (TMD) parton distribution functions and gluon Sivers function. We estimate SSA for JLab, HERMES, COMPASS, and eRHIC energies using the color evaporation model of charmonium production, using an analytically obtained approximate solution of TMD evolution equations discussed in the literature. We find that there is a reduction in the asymmetry compared with our predictions for the earlier case considered by us, wherein the $Q^2$ dependence came only from DGLAP evolution of the unpolarized gluon densities and a different parametrization of the TMD Sivers function was used.