Small x gluon from exclusive J/psi production

Understand

Exclusive J/psi production, gamma* p -> J/psi p, offers a unique opportunity to determine the gluon density of the proton in the small x domain.

• We use the available HERA data to determine the gluon distribution in the region 10^{-4} <~ x <~ 10^{-2} and 2 <~ Q^2 <~ 10 GeV^2, where the uncertainty on the gluon extracted from the global parton analyses is large.
• The gluon density is found to be approximately flat at the lower scale; it is compared with those of recent global analyses.