Fragmentation contributions to J/psi photoproduction at HERA

Abstract

We compute leading-power fragmentation corrections to J/psi photoproduction at DESY HERA, making use of the nonrelativistic QCD factorization approach. Our calculations include parton production cross sections through order alpha(2)(s), fragmentation functions though order alpha(2)(s), and leading logarithms of the transverse momentum divided by the charm-quark mass to all orders in as. We find that the leading-power fragmentation corrections, beyond those that are included through next-to-leading order in as, are small relative to the fixed-order contributions through next-to-leading order in as. Consequently, an important discrepancy remains between the experimental measurements of the J/psi photoproduction cross section and predictions that make use of nonrelativistic-QCD long-distance matrix elements that are extracted from the J/psi hadroproduction cross-section and polarization data.