Direct photon production in Pb-Pb collisions at root s(NN)=2.76 TeV

Adam J., Adamova D., Aggarwal M. M., Rinella G. A., Agnello M., Agrawal N., ...More

PHYSICS LETTERS B, vol.754, pp.235-248, 2016 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 754
  • Publication Date: 2016
  • Doi Number: 10.1016/j.physletb.2016.01.020
  • Journal Name: PHYSICS LETTERS B
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.235-248
  • Bursa Uludag University Affiliated: No


Direct photon production at mid-rapidity in Pb-Pb collisions at root s(NN) = 2.76 TeV was studied in the transverse momentum range 0.9 < p(T) < 14 GeV/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 p(T) greater than or similar to 5 GeV/c. Direct photon spectra down to p(T) approximate to 1 GeV/c could be extracted for the 20-40% and 0-20% centrality classes. The significance of the direct photon signal for 0.9 < p(T) < 2.1 GeV/c is 2.6 sigma for the 0-20% class. The spectrum in this p(T) range and centrality class can be described by an exponential with an inverse slope parameter of (297 +/- 12(stat) +/- 41(syst)) MeV. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties. (C) 2016 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.