Looking for the gluonic EMC effect in associated $J/ψ$ + $γ$ production

Abstract

We study the associated production of $ J/ψ + γ$ in fixed-target experiments with nuclear targets as well as at the relativistic heavy-ion collider (RHIC). We find that this process affords a very clean probe of $ρ_g$, the ratio of gluon density in a heavy nucleus to that of a proton. The combined $x$ range thus available can be used to discriminate between the predictions of different models of the EMC effect for $ρ_g$.