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

J. Adam, D. Adamova, M.M. Aggarwal, G. Aglieri Rinella, Maria Agnello, N. Agrawal, Z. Ahammed, S. U. Ahn, S. Aiola, A. Akindinov, B. Alessandro, J. Alme, A. Alkin, C. Andrei, Ian Bearden, Hans Bøggild, Christian Holm Christensen, Kristjan Herlache Gulbrandsen, Jens Jørgen Gaardhøje, Hans Hjersing DalsgaardBørge Svane Nielsen, Alexander Colliander Hansen, Ante Bilandzic, Marek Chojnacki, Valentina Zaccolo, You Zhou, Christian Alexander Bourjau

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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.

OriginalsprogEngelsk
TidsskriftPhysics Letters B
Vol/bind754
Sider (fra-til)235-248
ISSN0370-2693
DOI
StatusUdgivet - 10 mar. 2016

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