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

Scientific paper - Original scientific paper

• Author: S. Acharya
• Author: ...
• Author: Tome Antičić; MBZ: 218816
• Author: ...
• Author: Filip Erhardt; MBZ: 345132
• Author: ...
• Author: Sven Gotovac; MBZ: 108173
• Author: ...
• Author: Marko Jerčić; MBZ: 358125
• Author: ...
• Author: Petra Lončar; MBZ: 350591
• Author: ...
• Author: Eugen Mudnić; MBZ: 248856
• Author: ...
• Author: Mirko Planinić; MBZ: 213776
• Author: ...
• Author: Nikola Poljak; MBZ: 283732
• Author: ...
• Author: Goran Simatović; MBZ: 329845
• Author: ...
• Author: Antonija Utrobičić; MBZ: 342963
• Author: ...
• Author: Linda Vicković; MBZ: 242565
• Author: ...
• Author: S. Zou
• Collaboration: ALICE Collaboration
• Author's institution: University of Zagreb; Faculty of Science; (Department of Physics)
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract (english)

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.

• Keywords (english): 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
• Language: english
• Publication type: Scientific paper - Original scientific paper
• Publication status: Published
• Peer review: Peer review - international
• Publication version: Published version
• Journal title: Physical Review C
• Numbering: vol. 99, no. 2, 024912
• p-ISSN: 2469-9985
• e-ISSN: 2469-9993
• DOI: https://doi.org/10.1103/physrevc.99.024912
• URN:NBN: urn:nbn:hr:217:751812
• Publication: 2019
• Document URL: https://journals.aps.org/prc/abstract/10.1103/PhysRevC.99.024912
• Type of resource: Text
• Access conditions: Open access
• Public note: ©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.
• Created on: 2020-03-01 19:02:38