Direct photon production in Pb–Pb collisions at √sNN = 2.76 TeV
ALICE Collaboration. (2016). Direct photon production in Pb–Pb collisions at √sNN = 2.76 TeV. Physics Letters B, 754, 235-248. doi:10.1016/j.physletb.2016.01.020
Published inPhysics Letters B
Rak, Jan |
© 2016 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license. Funded by SCOAP3.
Direct photon production at mid-rapidity in Pb–Pb collisions at √sNN = 2.76 TeV was studied in the transverse momentum range 0.9 < pT < 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 pT 5 GeV/c. Direct photon spectra down to pT ≈ 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 < pT < 2.1 GeV/c is 2.6σ for the 0–20% class. The spectrum in this pT range 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. ...