In ultra-relativistic heavy ion collisions at the LHC, each nucleus acts as a source of high-energy quasi-real photons that can participate in scattering processes without causing either participating nucleus to break up and emit forward neutrons. This paper extends recent measurements of γ+A production in ultra-peripheral Pb+Pb collisions at sNN = 5. 02 TeV with forward neutron emission on exactly one side of the event. The data presented here was recorded by the ATLAS collaboration at the LHC in 2018, corresponding to a luminosity of 1. 72 nb^-1. These results examines 5. 02 TeV Pb+Pb collisions where neither nucleus breaks up (0n0n), providing a mixture of photon--pomeron (γ+I\!\!P), photon--photon (γ+γ), and peripheral photonuclear (γ+A) events. The different processes are statistically separated via a template fit of the minimum rapidity gap distribution. The kinematics of the hard processes are determined from R = 0. 4 jets reconstructed using the anti-kₜ algorithm. The statistical separation of the different processes then allows for the first measurement of γ+I\!\!P cross-sections in nuclear collisions at the LHC. The rate for electromagnetic dissociation of 0n0nγ+A events is also measured and compared to the analogous result from collisions with single-sided neutron emission. These comparisons support the hypothesis that γ+A events without forward neutron emission select a more peripheral class of γ+A collisions.
Aad et al. (Thu,) studied this question.