Small x gluon from exclusive J/ψJ/ψ production

Exclusive J/ψJ/ψ production, γ∗p→J/ψpγ∗p→J/ψp, 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≲10−210−4≲x≲10−2 and 2≲Q2≲10 GeV22≲Q2≲10 GeV2, 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.