Geometric Scaling and Gluon Saturation at the EIC

Understanding the structure of protons and nuclei in terms of quarks and gluons is one of the key goals in science. Recent results from RHIC suggest the existence of a new state of matter known as gluon saturation. The idea is, at high energies, gluons, due to their self-interactions,multiply rapidly; however, when their density becomes very large, recombination effects set in, leading to saturation where the gluon density stops growing. One of the primary objectives of the upcoming Electron-Ion Collider (EIC) in the US is to probe this saturation regime. This work presents the first study of it in nuclei via exclusive J/ψ production in e+Au collisions. To pin down this effect, a multipronged approach is essential, examining saturation across a range of observables.

Geometric scaling is an elegant signature of such physics, where the cross sections scale with the saturation scale. We propose to investigate geometric scaling for exclusive vector meson production at the EIC by analyzing pseudo data generated with SARTRE, a Monte Carlo event generator designed for this process, to test the scaling hypothesis and its universality across different nuclear targets. Additionally, studying the differential cross section as a function of momentum transfer allows us to probe the spatial distribution of gluons inside the target. This work directly supports the EIC’s science goals and helps shape expectations for future experimental data.