Probing nonrelativistic QCD factorization in polarized J/psi photoproduction at next-to-leading order

TL;DR

This paper performs the first NLO analysis of polarized J/psi photoproduction within NRQCD, including relativistic corrections, and compares theoretical predictions with experimental data to test the factorization formalism.

Contribution

It provides a comprehensive NLO calculation of J/psi polarization observables including relativistic effects, advancing the understanding of NRQCD factorization at the quantum level.

Findings

Overall agreement with experimental polarization data is satisfactory.

NRQCD describes J/psi yield better than polarization observables.

Relativistic corrections are significant in polarization predictions.

Abstract

We analyze the polarization observables of J/psi photoproduction at next-to-leading order (NLO) within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD). This is the first NLO study of heavy-quarkonium polarization including the full relativistic corrections due to the intermediate ^1S_0^{[8]}, ^3S_1^{[8]}, and ^3P_J^{[8]} color-octet (CO) states in the worldwide endeavor to test NRQCD factorization at the quantum level. We present theoretical predictions in the helicity, target, and Collins-Soper frames of DESY HERA, evaluated using the CO long-distance matrix elements previously extracted through a global fit to experimental data of unpolarized J/psi production, and confront them with recent measurements by the H1 and ZEUS Collaborations. We find the overall agreement to be satisfactory, but the case for NRQCD to be not as strong as for the J/psi yield.