J/Psi production in ultra-peripheral heavy-ion collisions at RHIC

In recent years the STAR Collaboration collected a large sample
of ultra-peripheral heavy-ion collisions. The photoproduction of
J/Psi vector mesons is sensitive to the gluon content of the target
nucleon or nucleus. We will present results from a statistically
large sample of J/Psi production in Au+Au collisions. A significant
result comes from the study of the pT distributions, which clearly
show two components, from scattering off the entire Au nucleus or off
individual nucleons inside the nucleus. From a smaller sample of J/Psi
production in p+Au collisions, with polarized protons, we will discuss
the status of a first study of the asymmetry of J/Psi production.
A non-zero asymmetry would be the first measure of the generalized
parton distribution, E, for gluons, which is connected with the
orbital angular momentum of partons in the nucleon. The present study
is a proof-of-principle, and we will discuss the possibilities with
larger data samples from future polarized p+p and p+Au RHIC runs.