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

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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 ¹S₀[⁸], ³S₁[⁸], and ³Pⱼ[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.