Direct photon production in Pb-Pb collisions at
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Direct photon production at mid-rapidity in Pb–Pb collisions at rc">rce" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si1.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=1c8185232f9746b818569f8c750d7a2c">View the MathML sou<font color=rce" style="margin-top: -5px; vertical-align: middle" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0370269316000320-si1.gif">ript>rder="0" style="vertical-align:bottom" width="105" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0370269316000320-si1.gif">ript>r hidden">rflow="scroll">rt>row>srow>row>riant="normal">NNrow>rt>=2.76 TeV was studied in the transverse momentum range rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si148.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=0013d3c9759dbd106f0bce3f81d2dae8" title="Click to view the MathML source">0.9<pT<14 GeV/cr hidden">rflow="scroll">0.9<row>prow>row>riant="normal">Trow><14 GeVretchy="false">/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si4.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=1166737fefdecce3d6290006e66f4e08" title="Click to view the MathML source">e+er hidden">rflow="scroll">row>erow>row>+row>row>erow>row>row> 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 rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si5.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=f876eeae8231e04158b538b59eb9bcfd" title="Click to view the MathML source">pT≳5 GeV/cr hidden">rflow="scroll">row>prow>row>riant="normal">Trow>5 GeVretchy="false">/c. Direct photon spectra down to rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si6.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=145471da8223133907c91fcc1011f6da" title="Click to view the MathML source">pT≈1 GeV/cr hidden">rflow="scroll">row>prow>row>riant="normal">Trow>1 GeVretchy="false">/c could be extracted for the 20–40% and 0–20% centrality classes. The significance of the direct photon signal for rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si7.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=4067fc100418e5d9dc8ef576fcc34c21" title="Click to view the MathML source">0.9<pT<2.1 GeV/cr hidden">rflow="scroll">0.9<row>prow>row>riant="normal">Trow><2.1 GeVretchy="false">/c is 2.6σ   for the 0–20% class. The spectrum in this rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si8.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=aa58cb03581d230341ba1ff810fef8b0" title="Click to view the MathML source">pTr hidden">rflow="scroll">row>prow>row>riant="normal">Trow> range and centrality class can be described by an exponential with an inverse slope parameter of rc">rmulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316000320&_mathId=si9.gif&_user=111111111&_pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=2e8066a435697eed598476449755381f" title="Click to view the MathML source">(297±12stat±41syst) MeVr hidden">rflow="scroll">retchy="false">(297±row>12row>row>statrow>±row>41row>row>systrow>retchy="false">) MeV. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.

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