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.
Titolo: | Direct photon production in Pb-Pb collisions at √sNN = 2.76 TeV | |
Autori: | ||
Data di pubblicazione: | 2016 | |
Rivista: | ||
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 < 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. | |
Handle: | http://hdl.handle.net/11368/2878483 | |
Digital Object Identifier (DOI): | http://dx.doi.org/10.1016/j.physletb.2016.01.020 | |
URL: | http://www.sciencedirect.com/science/article/pii/S0370269316000320 | |
Appare nelle tipologie: | 1.1 Articolo in Rivista |
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