Soft-Dielectron Excess in Proton-Proton Collisions at root s=13 TeV

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A Large Ion Collider Experiment Collaboration , Acharya , S , Adamova , D , Kim , D J , Krizek , F , Novitzky , N , Parkkila , J E , Rak , J , Rasanen , S S , Rytkönen , H M , Saarimäki , O A M , Slupecki , M , Trzaska , W H & Zhou , Z 2021 , ' Soft-Dielectron Excess in Proton-Proton Collisions at root s=13 TeV ' , Physical Review Letters , vol. 127 , no. 4 , 042302 . https://doi.org/10.1103/PhysRevLett.127.042302

Title: Soft-Dielectron Excess in Proton-Proton Collisions at root s=13 TeV
Author: A Large Ion Collider Experiment Collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Novitzky, N.; Parkkila, J. E.; Rak, J.; Rasanen, S. S.; Rytkönen, Heidi Maria; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H.; Zhou, Z.
Contributor: University of Helsinki, University of Jyväskylä
University of Helsinki, The Czech Academy of Sciences
University of Helsinki, University of Tsukuba
University of Helsinki, University of Jyväskylä
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, University of Jyväskylä
University of Helsinki, University of Bergen
Date: 2021-07-23
Language: eng
Number of pages: 13
Belongs to series: Physical Review Letters
ISSN: 0031-9007
URI: http://hdl.handle.net/10138/333435
Abstract: A measurement of dielectron production in proton-proton (pp) collisions at root s = 13 TeV, recorded with the ALICE detector at the CERN LHC, is presented in this Letter. The data set was recorded with a reduced magnetic solenoid field. This enables the investigation of a kinematic domain at low dielectron (ee) invariant mass m(ee) and pair transverse momentum p(T,ee) that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of m(ee), p(T,ee), and event multiplicity dNch=d.. The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured eta/pi(0) ratio in pp and proton-nucleus collisions, assuming that this ratio shows no strong dependence on collision energy at low transverse momentum. Comparison of the measured dielectron yield to the hadronic cocktail at 0.15 < m(ee) < 0.6 GeV/c(2) and for p(T,ee) < 0.4 GeV/c indicates an enhancement of soft dielectrons, reminiscent of the "anomalous" soft-photon and soft-dilepton excess in hadron-hadron collisions reported by several experiments under different experimental conditions. The enhancement factor over the hadronic cocktail amounts to 1.61 +/- 0.13(stat) +/- 0.17(syst, data) +/- 0.34osyst; cocktailTHORN in the ALICE acceptance. Acceptance-corrected excess spectra in mee and pT; ee are extracted and compared with calculations of dielectron production from hadronic bremsstrahlung and thermal radiation within a hadronic many-body approach.
Subject: 114 Physical sciences
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