Direct photon production in Pb-Pb collisions at
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Direct photon production at mid-rapidity in Pb–Pb collisions at pan id="mmlsi1" class="mathmlsrc">itle="View the MathML source" 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"><img class="imgLazyJSB inlineImage" height="15" width="105" alt="View the MathML source" 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">ipt><img height="15" border="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">ipt>pan class="mathContainer hidden">pan class="mathCode">img="si1.gif" overflow="scroll">i>si>i mathvariant="normal">NNi>=2.76 TeVpan>pan>pan> was studied in the transverse momentum range pan id="mmlsi148" class="mathmlsrc">pan class="formulatext 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/cpan>pan class="mathContainer hidden">pan class="mathCode">img="si148.gif" overflow="scroll">0.9<i>pi>i mathvariant="normal">Ti><14 GeV/i>ci>pan>pan>pan>. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the pan id="mmlsi4" class="mathmlsrc">pan class="formulatext 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">ep>+p>ep>&minus;p>pan>pan class="mathContainer hidden">pan class="mathCode">img="si4.gif" overflow="scroll">p>i>ei>+p>p>i>ei>&minus;p>pan>pan>pan> 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 pan id="mmlsi5" class="mathmlsrc">pan class="formulatext 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/cpan>pan class="mathContainer hidden">pan class="mathCode">img="si5.gif" overflow="scroll">i>pi>i mathvariant="normal">Ti>≳5 GeV/i>ci>pan>pan>pan>. Direct photon spectra down to pan id="mmlsi6" class="mathmlsrc">pan class="formulatext 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&asymp;1 GeV/cpan>pan class="mathContainer hidden">pan class="mathCode">img="si6.gif" overflow="scroll">i>pi>i mathvariant="normal">Ti>&asymp;1 GeV/i>ci>pan>pan>pan> could be extracted for the 20–40% and 0–20% centrality classes. The significance of the direct photon signal for pan id="mmlsi7" class="mathmlsrc">pan class="formulatext 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/cpan>pan class="mathContainer hidden">pan class="mathCode">img="si7.gif" overflow="scroll">0.9<i>pi>i mathvariant="normal">Ti><2.1 GeV/i>ci>pan>pan>pan> is 2.6σ   for the 0–20% class. The spectrum in this pan id="mmlsi8" class="mathmlsrc">pan class="formulatext 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">pTpan>pan class="mathContainer hidden">pan class="mathCode">img="si8.gif" overflow="scroll">i>pi>i mathvariant="normal">Ti>pan>pan>pan> range and centrality class can be described by an exponential with an inverse slope parameter of pan id="mmlsi9" class="mathmlsrc">pan class="formulatext 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&plusmn;12p>statp>&plusmn;41p>systp>) MeVpan>pan class="mathContainer hidden">pan class="mathCode">img="si9.gif" overflow="scroll">(297&plusmn;p>12statp>&plusmn;p>41systp>) MeVpan>pan>pan>. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.

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