Direct photon production at mid-rapidity in Pb-Pb collisions at √sNN=2.76 TeV was studied in the transverse momentum range 0.9<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 pTâ1 GeV/c could be extracted for the 20-40% and 0-20% centrality classes. The significance of the direct photon signal for 0.9<2.1 GeV/c is 2.6Ï 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.
Direct photon production in Pb-Pb collisions at sqrt(s_{NN}) = 2.76 TeV
DE CARO, ANNALISA;DE GRUTTOLA, DANIELE;DE PASQUALE, Salvatore;FUSCO GIRARD, Mario;MENINNO, ELISA;PAGANO, PAOLA;VIRGILI, Tiziano;CALIVA', Alberto
2016-01-01
Abstract
Direct photon production at mid-rapidity in Pb-Pb collisions at √sNN=2.76 TeV was studied in the transverse momentum range 0.9<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 pTâ1 GeV/c could be extracted for the 20-40% and 0-20% centrality classes. The significance of the direct photon signal for 0.9<2.1 GeV/c is 2.6Ï 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.File | Dimensione | Formato | |
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Direct-photon-production-in-PbPb-collisions-at-s276-TeV2016Physics-Letters-Section-B-Nuclear-Elementary-Particle-and-HighEnergy-PhysicsOpen-Access.pdf
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