Measurement of Direct Photons in pp and Pb-Pb Collisions with ALICE

作者：Wilde Martin^*

来源：Nuclear Physics A, 2013, 904: 573C-576C.

DOI：10.1016/j.nuclphysa.2013.02.079

The measurement of the direct photon transverse momentum spectrum in Pb-Pb collisions at root s(NN) = 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 p(T) the result is in agreement with pQCD predictions. The low p(T) signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as T-LHC = 304 +/- 51(syst+stat) MeV. For a baseline measurement the analysis is performed for protonproton collisions at root s = 7 TeV and for peripheral (40-80%) Pb-Pb collisions. Both results show no low pr direct-photon signal and are in agreement with pQCD calculations.

• 出版日期2013-5-2