Direct photon measurement in Pb-Pb collisions at with ALICE

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• 作者：Baldo Sahlmü ; ller ; for the ALICE Collaboration
• 关键词：photons ; direct photons ; thermal radiation ; electroweak probes ; QGP
• 刊名：Nuclear Physics A
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：956
• 期：Complete
• 页码：421-424
• 全文大小：220 K

文摘

The ALICE experiment has measured the direct photon spectra in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\text{TeV}$ for three different centrality selections. The measurement was performed emplying a method utilizing conversion of photons into e⁺e⁻$e^{+}{e}^{-}$ pairs in the detector material, and a method using the PHOS calorimeter. The two measurements were combined in order to measure direct photons over a broad transverse momentum range of 0.9<p_T<14 GeV/c$0.9<p_T<14\text{GeV}/c$. A direct photon signal was observed in the thermal region 0.9<p_T<2.1 GeV/c$0.9<p_T<2.1\text{GeV}/c$, with a significance of 2.6σ   in the 20% most central collisions. The corresponding direct photon spectrum can be described by an exponential with an inverse slope parameter of (304±11^stat±40^syst$304\pm {11}^{stat}\pm {40}^{syst}$) MeV, without subtracting the hard scattering component, which is somewhat larger than the inverse slope parameter of the direct photon spectrum at RHIC energies. Within uncertainties, the data can be described by different models for photon production in heavy-ion collisions. These proceedings provide a summary of the results published in [J. Adam, others (ALICE Collaboration), Direct photon production in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\text{TeV}$, arXiv:1509.07324] and [J. Adam, others (ALICE Collaboration), Supplemental figures: Direct photon production in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\text{TeV}$. URL https://cds.cern.ch/record/2102398].