Color Octet Contribution to J/psi Photoproduction Asymmetries

TL;DR

This paper examines how color octet contributions in NRQCD affect J/psi photoproduction asymmetries, revealing large uncertainties that hinder gluon polarization measurements but suggest potential for testing NRQCD and gluon distributions.

Contribution

It demonstrates that color octet effects introduce significant uncertainties in asymmetry predictions, impacting the feasibility of using J/psi photoproduction to measure gluon polarization.

Findings

Color octet contributions cause large uncertainties in asymmetry predictions.

Precise gluon polarization measurement via J/psi asymmetries is challenging.

Potential to test NRQCD factorization and gluon distributions with low inelasticity data.

Abstract

We investigate $J/\psi$ photoproduction asymmetries in the framework of the NRQCD factorization approach. It is shown that the color octet contribution leads to large uncertainties in the predicted asymmetries which rules out the possibility to precisely measure the gluon polarization in the nucleon through this final state. For small values of the color octet parameters being compatible with $J/\psi$ photoproduction data it appears possible that a measurement of $J/\psi$ asymmetries could provide a new test for the NRQCD factorization approach, on one hand, or a measurement of the polarized gluon distribution from low inelasticity events $(z<0.7)$, on the other