Probing Nuclear Parton Distributions and their Radial Dependence using Jet Photoproduction in Ultra-Peripheral Pb+Pb Collisions with the ATLAS Detector at the LHC

by Benjamin Gilbert (Lawrence Livermore National Laboratory)

Tuesday 1 Sept 2026, 11:00 → 13:00 US/Eastern

Small seminar room (Bldg 510 Physics)

Abstract: In ultra-peripheral collisions (UPCs), emitted photons may participate in a hard-scattering process with partons within the struck nucleus, providing a clean, energetic probe of its parton distributions. This talk presents measurements of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, forward neutron emission, and rapidity gaps are then used to statistically separate inclusive photo-nuclear, photo-diffractive, and two-photon hard-scattering processes. The measured photo-nuclear cross-sections are compared to theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not well constrained by world data, demonstrating the potential of these data to provide a strong new constraint on nuclear PDF effects. Additionally, measurements of jet production in UPCs where neither nucleus emits forward neutrons are performed. These processes provide a novel method for probing the radial dependence of nuclear modifications within the target. Studies of jet production without forward neutron emission also make possible the first measurement of diffractive jet photo-production in nuclear collisions, which will provide direct input for constraining existing models. The implications of each of these measurements for possible future measurements at the EIC will also be discussed.