Journal Article Direct photon production in Pb–Pb collisions at √sNN=2.76TeV

ALICE Collaboration  ,  Busch, O.  ,  Chujo, T.  ,  Esumi, S.  ,  Miake, Y.

754pp.235 - 248 , 2016-03 , Elsevier B.V.
Direct photon production at mid-rapidity in Pb–Pb collisions at √sNN=2.76TeVwas studied in the transverse momentum range 0.9 <pT<14GeV/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the e+e−pair reconstructed in the central tracking system. The results of the two methods were combined and direct photon spectra were measured for the 0–20%, 20–40%, and 40–80% centrality classes. For all three classes, agreement was found with perturbative QCD calculations for pT5GeV/c. Direct photon spectra down to pT≈1GeV/ccould be extracted for the 20–40% and 0–20% centrality classes. The significance of the direct photon signal for 0.9<pT<2.1GeV/cis 2.6σfor the 0–20% class. The spectrum in this pTrange and centrality class can be described by an exponential with an inverse slope parameter of (297±12stat±41syst)MeV. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.

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