Constraints on nuclear gluon densities from J/ψ data

The gluon density in nuclei, GA(x), is poorly constrained at all x from the current DIS and Drell-Yan data. In this Letter, we point out that J/ψ production measured in proton-nucleus collisions at √(spA)=38.8 GeV by the E866 Collaboration puts stringent constraints on the x-dependence of the GW/GBe ratio in the x=2x10-2-10-1 range. The E866 data suggest a rather mild x-dependence of GW/GBe, and consequently tend to favour nDS and HKM sets, rather than the nDSg, EKS98, and EPS08 parametrizations which exhibit a larger shadowing and anti-shadowing