Direct photon production in Pb-Pb collisions at
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- 作者：ALICE Collaboration
- 刊名：Physics Letters B
- 出版年：2016
- 出版时间：10 March 2016
- 年：2016
- 卷：754
- 期：Complete
- 页码：235-248
- 全文大小：2413 K
文摘
Direct photon production at mid-rapidity in Pb–Pb collisions at pan id="mmlsi1" class="mathmlsrc">pii=S0370269316000320&_rdoc=1&_issn=03702693&md5=1c8185232f9746b818569f8c750d7a2c">![View the MathML source]()
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p://origin-ars.els-cdn.com/content/image/1-s2.0-S0370269316000320-si1.gif"> pt>pan class="mathContainer hidden">pan class="mathCode"> pan> 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/c pan>pan class="mathContainer hidden">pan class="mathCode"> 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>− p> pan>pan class="mathContainer hidden">pan class="mathCode"> 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/c pan>pan class="mathContainer hidden">pan class="mathCode"> 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≈1 GeV/c pan>pan class="mathContainer hidden">pan class="mathCode"> 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/c pan>pan class="mathContainer hidden">pan class="mathCode"> 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">pT pan>pan class="mathContainer hidden">pan class="mathCode"> 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±12p>stat p>±41p>syst p>) MeV pan>pan class="mathContainer hidden">pan class="mathCode"> pan> pan> pan>. State-of-the-art models for photon production in heavy-ion collisions agree with the data within uncertainties.