Fragmentation contributions to J/ψ photoproduction at HERA

We compute leading-power fragmentation corrections to J/ψ photoproduction at DESY HERA, making use of the nonrelativistic QCD factorization approach. Our calculations include parton production cross sections through order αs3, fragmentation functions though order αs2, and leading logarithms of the transverse momentum divided by the charm-quark mass to all orders in αs. We find that the leading-power fragmentation corrections, beyond those that are included through next-to-leading order in αs, are small relative to the fixed-order contributions through next-to-leading order in αs. Consequently, an important discrepancy remains between the experimental measurements of the J/ψ photoproduction cross section and predictions that make use of nonrelativistic-QCD long-distance matrix elements that are extracted from the J/ψ hadroproduction cross-section and polarization data.