Abstract
The measurement of the direct photon transverse momentum spectrum in Pb–Pb collisions at sNN=2.76 TeV with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0–40% most central collisions below 4 GeV/c that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of pT the result is in agreement with pQCD predictions. The low pT signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as TLHC=304±51syst+stat MeV. For a baseline measurement the analysis is performed for proton-proton collisions at s=7 TeV and for peripheral (40–80%) Pb–Pb collisions. Both results show no low pT direct-photon signal and are in agreement with pQCD calculations.
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