Probing Gluons in Nuclei: the Case of $η'$

Abstract

Using the recently proposed $gg --> eta'$ effective vertex, we investigate the production of $η'$ from gluon fusion in $pA$ collisions. We show that measuring $η'$ production cross-section at moderate $x_{η'}$ yields direct information on the small $x$ gluon distribution function of the nucleus. At RHIC, the smallest accessible $x$ turns out to be $O(10^{-5})$ and at LHC, it is $O(10^{-8})$. Therefore, $η'$ is an excellent probe of the Color Glass Condensate.