Measurement of Direct Photons in pp and Pb–Pb Collisions with ALICE

Autor: Martin Wilde
Rok vydání: 2013
Předmět:
Zdroj: Nuclear Physics A. :573c-576c
ISSN: 0375-9474
DOI: 10.1016/j.nuclphysa.2013.02.079
Popis: The measurement of the direct photon transverse momentum spectrum in Pb-Pb collisions at \unit[$\sqrt{s_{_{NN}}}=2.76]{TeV}$ with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0-40% most central collisions below \unit[4]{GeV/$\mathrm{c}$} that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of $p_{\mathrm{T}}$ the result is in agreement with pQCD predictions. The low $p_{\mathrm{T}}$ signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as $T_{\mathrm{LHC}}=\unit[304\pm 51^{\mathrm{syst+stat}}]{MeV}$. For a baseline measurement the analysis is performed for proton-proton collisions at \unit[$\sqrt{s}=7]{TeV}$ and for peripheral (40-80%) Pb-Pb collisions. Both results show no low $p_\mathrm{T}$ direct-photon signal and are in agreement with pQCD calculations. The measurement of the direct photon transverse momentum spectrum in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0-40% most central collisions below 4 GeV/c that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of p_T the result is in agreement with pQCD predictions. The low p_T signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as T_L_H_C=304+/-51^s^y^s^t^+^s^t^a^t MeV. For a baseline measurement the analysis is performed for proton-proton collisions at s=7 TeV and for peripheral (40-80%) Pb-Pb collisions. Both results show no low p_T direct-photon signal and are in agreement with pQCD calculations. The measurement of the direct photon transverse momentum spectrum in Pb–Pb collisions at sNN=2.76 TeV with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0–40% most central collisions below 4 GeV/c that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of pT the result is in agreement with pQCD predictions. The low pT signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as TLHC=304±51syst+stat MeV . For a baseline measurement the analysis is performed for proton-proton collisions at s=7 TeV and for peripheral (40–80%) Pb–Pb collisions. Both results show no low pT direct-photon signal and are in agreement with pQCD calculations. The measurement of the direct photon transverse momentum spectrum in Pb-Pb collisions at \unit[$\sqrt{s_{_{NN}}}=2.76]{TeV}$ with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0-40% most central collisions below \unit[4]{GeV/$\mathrm{c}$} that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of $p_{\mathrm{T}}$ the result is in agreement with pQCD predictions. The low $p_{\mathrm{T}}$ signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as $T_{\mathrm{LHC}}=\unit[304\pm 51^{\mathrm{syst+stat}}]{MeV}$. For a baseline measurement the analysis is performed for proton-proton collisions at \unit[$\sqrt{s}=7]{TeV}$ and for peripheral (40-80%) Pb-Pb collisions. Both results show no low $p_\mathrm{T}$ direct-photon signal and are in agreement with pQCD calculations.
Databáze: OpenAIRE
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