Measurement of isolated photon production in pp and PbPb collisions at

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 |η| | η | 1.44 and transverse energies E T E T between 20 and 80 GeV with the CMS detector at the LHC. The measured E T E T 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 E T -differential yields, scaled by the number of incoherent nucleon–nucleon collisions, is consistent with unity for all PbPb reaction centralities.