Quantum chromodynamics predicts that at sufficiently high energies the gluon density inside hadrons enters a regime, known as gluon saturation, where gluon splitting and recombination reach a dynamic equilibrium. Diffractive photoproduction of J/ψ mesons is a particularly sensitive probe of this phe- nomenon, since it directly couples to the gluon distribution of the nucleus. With its unique coverage of photon–nucleon center-of-mass energies from about 20 to 800 GeV, the ALICE detector can study the energy dependence of J/ψ production across three orders of magnitude in Bjorken-x.

In this talk, I will present the latest ALICE measurements of the energy dependence of incoher- ent photonuclear J/ψ production in Pb–Pb ultra-peripheral collisions at √sNN = 5.02 TeV, analyzed in three Mandelstam-t intervals. While low-|t| production reflects the average gluon density in nu- clei, higher-|t| values probe gluon fluctuations at smaller spatial scales. The observed suppression of the cross-section growth with energy at large |t| relative to low |t| provides new evidence of gluon saturation–like dynamics, offering unprecedented constraints on models of QCD in the high-energy limit.