Nuclear Shadowing in inelastic photon-nucleus scattering in UPCs with forward neutrons

We argue that measurements of forward neutrons from nuclear breakup in inclusive high energy photon-nucleus (photon-A) scattering provide a novel complementary way to study small-x dynamics of QCD in heavy-ion ultraperipheral collisions (UPCs). Using the leading twist approach to nuclear shadowing, we calculate the distribution over the number of evaporation neutrons produced in photon-lead collisions at the LHC. We demonstrate that it allows one to determine the distribution over the number of wounded nucleons (inelastic collisions), which constrains the mechanism of nuclear shadowing of nuclear parton distributions and gives an access to their impact parameter dependence.