Direct photon production in Pb–Pb collisions at s NN = 2.76 TeV
We studied the direct photon production at mid-rapidity in Pb-Pb collisions at √sNN = 2.76 TeV 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. Our 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 greater than or similar to 5 GeV/c. Direct photon spectra down to pT approximate to 1 GeV/c could be extracted for the 20-40% and 0-20% centrality classes. Furthermore, the significance of the direct photon signal for 0.9 < pT < 2.1 GeV/c is 2.6 sigma 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.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- ALICE Collaboration
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1343515
- Journal Information:
- Physics Letters. Section B, Vol. 754; ISSN 0370-2693
- Publisher:
- Elsevier
- Country of Publication:
- United States
- Language:
- English
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