Direct photon production at low transverse momentum in proton-proton collisions at √s=2.76 and 8 TeV

Acharya, S. and Antičić, Tome and Erhardt, Filip and Gotovac, Sven and Jerčić, Marko and Lončar, Petra and Mudnić, Eugen and Planinić, Mirko and Poljak, Nikola and Simatović, Goran and Utrobičić, Antonija and Vicković, Linda and Zou, S. (ALICE Collaboration) (2019) Direct photon production at low transverse momentum in proton-proton collisions at √s=2.76 and 8 TeV. Physical Review C, 99 (2). p. 24912. ISSN 2469-9985

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Abstract

Measurements of inclusive and direct photon production at midrapidity in pp collisions at s=2.76 and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of pT<0.4, 10> GeV/c and pT<0.3, 16> GeV/c, respectively. Photons are detected with the electromagnetic calorimeter (EMCal) and via reconstruction of e+e− pairs from conversions in the ALICE detector material using the central tracking system. For the final measurement of the inclusive photon spectra the results are combined in the overlapping pT interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio Rγ, which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation. An additional hybrid method, combining photons reconstructed from conversions with those identified in the EMCal, is used for the combination of the direct photon excess ratio Rγ, as well as the extraction of direct photon spectra or their upper limits. While no significant signal of direct photons is seen over the full pT range, Rγ for pT>7 GeV/c is at least one σ above unity and consistent with expectations from next-to- leading order pQCD calculations.

Item Type: Article
Keywords: photon: direct production, photon: spectrum, photon: production, pp: scattering, photon: decay, calorimeter: electromagnetic, transverse momentum: low, quantum chromodynamics: perturbation theory, higher-order: 1, ALICE, tracking detector, CERN LHC Coll, hybrid
Date: 2019
Number of Pages: 19
Subjects: NATURAL SCIENCES > Physics
Additional Information: ©2019 CERN, for the ALICE Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Received 30 March 2018; Published 21 February 2019.
Divisions: Faculty of Science > Department of Physics
Publisher: American Physical Society
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 28 Mar 2019 13:30
Last Modified: 28 Mar 2019 13:30
URI: http://digre.pmf.unizg.hr/id/eprint/5903

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