Speaker
Description
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 $\alpha_s^3$, fragmentation functions though
order $\alpha_s^2$, and leading logarithms of the transverse momentum
divided by the charm-quark mass to all orders in $\alpha_s$. We find
that the leading-power fragmentation corrections, beyond those that are
included through next-to-leading order in $\alpha_s$, are small relative
to the fixed-order contributions through next-to-leading order in
$\alpha_s$. 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.
