$J/\psi$ Production in Polarized and Unpolarized $ep$ Collision and Sivers and $\cos2\phi$ Asymmetries

TL;DR

This paper investigates azimuthal asymmetries in $J/\psi$ production during polarized and unpolarized $ep$ collisions, using TMD formalism and NRQCD, revealing insights into gluon distributions and matching experimental data.

Contribution

It introduces a detailed calculation of Sivers and $\cos2\phi$ asymmetries in $J/\psi$ production using TMDs and NRQCD, providing new insights into gluon TMDs and their evolution.

Findings

Sivers asymmetry at $z=1$ is negative, aligning with COMPASS data.

The $\cos2\phi$ asymmetry is sizable, indicating the presence of linearly polarized gluons.

TMD evolution significantly affects the Sivers asymmetry.

Abstract

We calculate the Sivers and $\cos2\phi$ azimuthal asymmetries in $J/\psi$ production in polarized and unpolarized semi-inclusive $ep$ collision respectively, using the formalism based on transverse momentum dependent parton distributions (TMDs). Non-relativistic QCD based color octet model is employed for calculating the $J/\psi$ production rate. The Sivers asymmetry in this process directly probes the gluon Sivers function. The estimated Sivers asymmetry at $z=1$ is negative which is in good agreement with COMPASS data. We also investigate the effect of TMD evolution on the Sivers asymmetry. The $\cos2\phi$ asymmetry is sizable and probes the linearly polarized gluon distribution in an unpolarized proton.