Predictions for the spatial distribution of gluons in the initial nuclear state

We make predictions for the t-differential cross section of exclusive vector meson production (EVMP) in electron–ion collisions, with the aim of comparing DGLAP evolution to CGC models. In the current picture for the high-energy nucleus, nonlinear effects need to be understood in terms of low-x   gluon radiation and recombination as well as how this leads to saturation. EVMP grants experimental access to the edge region of the highly-boosted nuclear wavefunction, where the saturation scale for CGC calculations becomes inaccessible to pQCD. On the other hand, DGLAP evolution requires careful consideration of unitarity effects. The existing J/ψJ/ψ photoproduction data in ep collisions provides a baseline for these theoretical calculations. Under different small-x frameworks we obtain a measurable distinction in both the shape and normalisation of the differential cross section predictions. These considerations are relevant for heavy-ion collisions because the initial state may be further constrained, thus aiding in quantitative study of the quark–gluon plasma.