e+A physics at a future Electron-Ion Collider

Abstract

A future Electron-Ion Colllider (EIC) is the ideal laboratory for studying the gluon distributions in both nucleons and nuclei for $\sqrt{s}$ = 63 - 158 (40 - 110) GeV/A for e+p (e+A) collisions. Whilst gluon distributions have been studied extensively in nucleons at HERA, there is very little information on them for $x <$ 0.1 in nuclei. The rapid increase in the gluon momentum distribution at low-$x$ in nucleons found at HERA, if not tamed, leads to the violation of the Froissart Unitarity Bound at small-$x$. This can be achieved in non-linear QCD by allowing for the recombination of low-$x$ gluons until saturation of gluon densities occurs. Understanding saturation is an important goal not just for QCD in general, but also in understanding the initial conditions of heavy-ion collisions in particular. In this paper, I describe the physics that will be explored by e+A collisions, where saturation is more easily explored in this mode at an EIC than in e+p collisions due to the large nuclear densities achieved.