title: Probing nonrelativistic QCD factorization in polarized J/ψ photoproduction at next-to-leading order.
abstract: We analyze the polarization observables of J/ψ photoproduction at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD). This is a complete next-to-leading-order study of heavy-quarkonium polarization including the full relativistic corrections due to the intermediate (1)S(0)([8]), (3)S(1)([8]), and (3)P(J)([8]) color-octet states closing a gap 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 color-octet long-distance matrix elements previously extracted through a global fit to experimental data of unpolarized J/ψ 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/ψ yield.
authors.affiliation: II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Butenschoen
authors.forename: Bernd A
authors.initials: BA
authors.lastname: Kniehl