Measurement of the inclusive isolated-photon production cross section in pp and Pb–Pb collisions at sNN=5.02 TeV

Abstract

Abstract The ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum ( $$p_{\textrm{T}}^{\gamma }$$ p T γ ), in Pb–Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $$\sqrt{s_{\textrm{NN}}}~=~5.02$$ s NN = 5.02 TeV. The photon transverse momentum range is between 10–14 and 40–140 GeV/ $$c$$ c , depending on the collision system and on the Pb–Pb centrality class. The result extends to lower $$p_{\textrm{T}}^{\gamma }$$ p T γ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $$|\eta ^{\gamma } | | η γ | 0.67 . The isolation selection is based on a charged particle isolation momentum threshold $$p_{\textrm{T}}^\mathrm{iso,~ch} = 1.5$$ p T iso , ch = 1.5 GeV/ $$c$$ c within a cone of radii $$R=0.2$$ R = 0.2 and 0.4. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb–Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z $$^{0}$$ 0 bosons from the CMS experiment, which are all found to be in agreement.