Measurement of inclusive isolated-photon cross-section with the ATLAS detector using the Frixione isolation prescription.

The differential cross-section for inclusive isolated-photon production in proton-proton collisions is measured at a center-of-mass energy of 13 TeV with the ATLAS detector, using an integrated luminosity of $36 {fb^{-1}}$. The differential cross-section is presented as a function of the photon transverse momentum in the $20\mbox{--}140 {GeV}$ range. The measurement is performed using two criteria for photon isolation: the standard fixed-cone approach and, for the first time, the Frixione isolation prescription, which requires the energy in a cone to vanish when its radius approaches zero. The Frixione isolation is used in theoretical calculations since it allows the rejection of the fragmentation contribution. To apply it experimentally, it’s necessary to use a discrete version, based on a finite set of cones, which still provides a good suppression of fragmentation photons and allows a coherent treatment of isolation between theoretical calculations and data analysis. The measurement is compared with the NLO Jetphox calculation and the Monte Carlo predictions from Pythia and Sherpa. The predictions provide a good description of the data within the experimental and theoretical uncertainties.