SSA in electroproduction of $J/\psi$ and QCD-evolved TMD's

TL;DR

This paper estimates the Sivers asymmetry in low virtuality photoproduction of J/psi, incorporating Q^2 evolution of TMD PDFs and Sivers functions, revealing a significant reduction compared to previous models and aligning with recent parametrizations.

Contribution

It introduces a comprehensive Q^2 evolution approach for TMDs in J/psi photoproduction, improving accuracy over earlier approximate methods.

Findings

Significant reduction in predicted asymmetry with Q^2 evolution.

Estimates are consistent with recent NLL-resummed parametrizations.

Comparison shows improved modeling of TMD evolution effects.

Abstract

We estimate Sivers asymmetry in low virtuality photoproduction of $J/\psi$ using color evaporation model and taking into account $Q^2$- evolution of transverse momentum dependent PDF's and Sivers function. There is a substantial reduction in asymmetry as compared to our previous analysis wherein the $Q^2$-dependance came only from DGLAP evolution of collinear part of TMDs. The estimates of asymmetry are comparable to our earlier estimates in which we had used analytical solution of only an approximated form of the evolution equations. We have also estimated asymmetry using the latest parametrization by Echevarria {\it et al.} which are based on an evolution kernel in which the perturbative part is resummed to NLL accuracy.