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

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The ALICE 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 .

Title: Soft-Dielectron Excess in Proton-Proton Collisions at root s=13 TeV
Author: The ALICE 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 organization: Helsinki Institute of Physics
Date: 2021-07-23
Language: eng
Number of pages: 13
Belongs to series: Physical Review Letters
ISSN: 0031-9007
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
Peer reviewed: Yes
Rights: cc_by
Usage restriction: openAccess
Self-archived version: publishedVersion

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