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

TL;DR

This is a complete next-to-leading-order study of heavy-quarkonium polarization including the full relativistic corrections due to the intermediate color-octet states closing a gap in the worldwide endeavor to test NRQCD factorization at the quantum level.

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.

Figures (1)

• Figure 1: (color online) NLO NRQCD predictions (solid lines) for $\lambda$ and $\nu$ as functions of $p_T$ and $z$ in the helicity, Collins-Soper, and target frames including theoretical uncertainties (shaded/yellow bands) compared to H1 Aaron:2010gz and ZEUS :2009br data. For comparison, also the NLO CSM (dot-dashed lines) predictions including theoretical uncertainties (hatched/blue bands) as well as the LO NRQCD (dashed lines) and LO CSM (dotted lines) ones are shown.