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

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http://hdl.handle.net/10138/300490

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The ALICE Collaboration , Acharya , S , Brücken , E J , Chang , B , Hilden , T E , Kim , D J , Litichevskyi , V , Mieskolainen , M M , Orava , R , Parkkila , J E , Rak , J , Räsänen , S S , Saarinen , S , Slupecki , M , Snellman , T W , Trzaska , W H , Vargyas , M & Viinikainen , J 2019 , ' Direct photon production at low transverse momentum in proton-proton collisions at root s=2.76 and 8 TeV ' , Physical Review C , vol. 99 , no. 2 , 024912 . https://doi.org/10.1103/PhysRevC.99.024912

Title: Direct photon production at low transverse momentum in proton-proton collisions at root s=2.76 and 8 TeV
Author: The ALICE collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J.
Contributor: University of Helsinki, Helsinki Institute of Physics
University of Helsinki, University of Jyväskylä
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, University of Jyväskylä
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, University of Jyväskylä
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, University of Jyväskylä
University of Helsinki, University of Jyväskylä
University of Helsinki, University of Jyväskylä
Date: 2019-02-21
Language: eng
Number of pages: 19
Belongs to series: Physical Review C
ISSN: 2469-9985
URI: http://hdl.handle.net/10138/300490
Abstract: Measurements of inclusive and direct photon production at midrapidity in pp collisions at root s = 2.76 and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of 0.4 < p(T) < 10 GeV/c and 0.3 < p(T) < 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 p(T), interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio R-gamma, 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 R-gamma, 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 p(T), range, R-gamma, for p(T), > 7 GeV/c is at least one sigma above unity and consistent with expectations from next-to-leading order pQCD calculations.
Subject: 114 Physical sciences
PB-PB COLLISIONS
QUARK-GLUON PLASMA
CHARGED-PARTICLE PRODUCTION
NEUTRAL PION
PREDICTIONS
PERSPECTIVE
DEPENDENCE
SINGLE
PP
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