Measurement of prompt photon production in sNN=8.16 TeV p + Pb collisions with ATLAS

Abstract

The inclusive production rates of isolated, prompt photons in p +Pbcollisions at √sNN=8.16TeV are studied with the ATLAS detector at the Large Hadron Collider using a dataset with an integrated luminosity of 165nb−1recorded in 2016. The cross-section and nuclear modification factor RpPbare measured as a function of photon transverse energy from 20GeV to 550GeV and in three nucleon–nucleon centre-of-mass pseudorapidity regions, (−2.83, −2.02), (−1.84, 0.91), and (1.09, 1.90). The cross-section and RpPbvalues are compared with the results of a next-to-leading-order perturbative QCD calculation, with and without nuclear parton distribution function modifications, and with expectations based on a model of the energy loss of partons prior to the hard scattering. The data disfavour a large amount of energy loss and provide new constraints on the parton densities in nuclei.