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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 ($$p_{\textrm{T}}^{\gamma }$$ ), in Pb–Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of$$\sqrt{s_{\textrm{NN}}}~=~5.02$$ 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$$p_{\textrm{T}}^{\gamma }$$ 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$$p_{\textrm{T}}^\mathrm{iso,~ch} = 1.5$$ 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.
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This content will become publicly available on January 1, 2026
Measurement of the inclusive isolated-photon production cross section in pp collisions at $$\mathbf {\sqrt{\textit{s}}=13}$$ TeV
Abstract The production cross section of inclusive isolated photons has been measured by the ALICE experiment at the CERN LHC in pp collisions at centre-of-momentum energy of$$\sqrt{s} =13$$ TeV collected during the LHC Run 2 data-taking period. The measurement is performed by combining the measurements of the electromagnetic calorimeter EMCal and the central tracking detectors ITS and TPC, covering a pseudorapidity range of$$|\eta ^{\gamma }|<0.67$$ and a transverse momentum range of$$7 GeV/$$c$$ . The result extends to lower$$p_\textrm{T}^{\gamma }$$ and$$x_\textrm{T}^{\gamma } = 2p_\textrm{T}^{\gamma }/\sqrt{s} $$ ranges, the lowest$$x_\textrm{T}^{\gamma }$$ of any isolated photon measurements to date, extending significantly those measured by the ATLAS and CMS experiments towards lower$$p_\textrm{T}^{\gamma }$$ at the same collision energy with a small overlap between the measurements. The measurement is compared with next-to-leading order perturbative QCD calculations and the results from the ATLAS and CMS experiments as well as with measurements at other collision energies. The measurement and theory prediction are in agreement with each other within the experimental and theoretical uncertainties.
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- PAR ID:
- 10599244
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- The European Physical Journal C
- Volume:
- 85
- Issue:
- 1
- ISSN:
- 1434-6052
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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