J/\psi polarization in photo-production up-to the next-to-leading order of QCD

TL;DR

This paper studies J/psi polarization in photoproduction at HERA using next-to-leading order QCD, finding significant discrepancies with experimental data and large theoretical uncertainties affecting predictions.

Contribution

It provides the first next-to-leading order QCD analysis of J/psi polarization in photoproduction, highlighting limitations of current theoretical models.

Findings

p_t and z distributions do not match experimental data well

Theoretical uncertainties are large for z distributions

Predicted p_t distributions are inconsistent with observations even at high p_t

Abstract

We investigate the J/psi polarization in photoproduction at the Hadron Electron Ring Accelerator(HERA) up to the next-to-leading order of QCD. The results show that the transverse momentum p_t and energy fraction z distributions of J/psi production do not agree with the observed ones very well. The theoretical uncertainties for the z distributions of the J/psi polarization parameters with respect to various choices of the renormalization and factorization scales are too large to give an accurate prediction. The uncertainties for the p_t distributions of these parameters are small when p_t>3GeV and the obtained p_t distributions can not describe the experimental data even in this region.