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Direct photon production in Pb–Pb collisions at √sNN=2.76 TeV
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Direct photon production in Pb–Pb collisions at √sNN=2.76 TeV

J. Adam, D. Adamová, M.M. Aggarwal, G. Aglieri Rinella, M. Agnello, N. Agrawal, Z. Ahammed, S.U. Ahn, S. Aiola, A. Akindinov, …
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 卷.754, 頁碼.235-248
03/2016
DOI: https://doi.org/10.1016/j.physletb.2016.01.020

摘要

Nuclear and High Energy Physics
Direct photon production at mid-rapidity in Pb–Pb collisions at s <sub>NN</sub> =2.76 TeV was studied in the transverse momentum range 0.9<p <sub>T</sub> <14 GeV/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the e <sup>+</sup> e <sup>−</sup> 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 p <sub>T</sub> ≳5 GeV/c. Direct photon spectra down to p <sub>T</sub> ≈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<p <sub>T</sub> <2.1 GeV/c is 2.6σ for the 0–20% class. The spectrum in this p <sub>T</sub> range and centrality class can be described by an exponential with an inverse slope parameter of (297±12 <sup>stat</sup> ±41 <sup>syst</sup> ) MeV. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.

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