Measurement of the inclusive isolated-photon production cross section in pp and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

Abstract

The ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum ($p_{\mathrm{T}}^{\gamma }$), in Pb$-$Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The photon transverse momentum range is between 10-14 and 40-140 GeV/$c$, depending on the collision system and on the Pb$-$Pb centrality class. The result extends to lower $p_{\mathrm{T}}^{\gamma }$ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $|{\eta }^{\gamma }|<0.67$. The isolation selection is based on a charged particle isolation momentum threshold $p_{\mathrm{T}}^{\mathrm{iso},\mathrm{ch}}=1.5$ GeV/$c$ within a cone of radii $R=0.2$ and $0.4$. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb$-$Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z${}^0$ bosons from the CMS experiment, which are all found to be in agreement.

45 pages, 17 captioned figures, 2 tables, authors from page 39, figures at http://alice-publications.web.cern.ch/node/11329

References in corpus (14)

• An Introduction to PYTHIA 8.2
• Tuning PYTHIA 8.1: the Monash 2013 Tune
• A new critical study of photon production in hadronic collisions
• Measurement of jet suppression in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV
• Measurement of direct photon production in p + p collisions at sqrt(s) = 200 GeV
• Quantitative constraints on the gluon distribution function in the proton from collider isolated-photon data
• Study of Z production in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV in the dimuon and dielectron decay channels
• Sensitivity of isolated photon production at TeV hadron colliders to the gluon distribution in the proton
• The Quark and Gluon Structure of the Proton
• $Z$ boson production in Pb+Pb collisions at $\sqrt{s_{\text{NN}}}$= 5.02 TeV measured by the ATLAS experiment
• Measurement of the ratio of cross sections for inclusive isolated-photon production in $pp$ collisions at $\sqrt{s}=13$ and $8$ TeV with the ATLAS detector
• The ALICE EMCal L1 trigger first year of operation experience
• Quenching of photon and pion spectra at intermediate RHIC energy
• Measurement of the inclusive isolated-photon production cross section in pp collisions at $\sqrt{s}$ = 13 TeV

Cited by in corpus (1)

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