Isolated photon production is measured in proton-proton and lead-lead collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range vertical bar eta vertical bar < 1.44 and transverse energies E-T between 20 and 80 GeV with the CMS detector at the LHC. The measured ET spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon E-T-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities. (C) 2012 CERN. Published by Elsevier BM. All rights reserved. RI Lokhtin, Igor/D-7004-2012; Perfilov, Maxim/E-1064-2012; Belyaev, Andrey/E-1540-2012; Boos, Eduard/D-9748-2012; Snigirev, Alexander/D-8912-2012; Tomei, Thiago/E-7091-2012; Focardi, Ettore/E-7376-2012; Raidal, Martti/F-4436-2012; Palla, Fabrizio/F-4727-2012; Gregores, Eduardo/F-8702-2012; Novaes, Sergio/D-3532-2012; Padula, Sandra /G-3560-2012; Lujan Center, LANL/G-4896-2012; Tinoco Mendes, Andre David/D-4314-2011; Flix, Josep/G-5414-2012; Fruhwirth, Rudolf/H-2529-2012; Chen, Jie/H-6210-2011; Torassa, Ezio/I-1788-2012
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