A1 Journal article (refereed)
Soft-Dielectron Excess in Proton-Proton Collisions at √s = 13 TeV (2021)

ALICE Collaboration. (2021). Soft-Dielectron Excess in Proton-Proton Collisions at √s = 13 TeV. Physical Review Letters, 127(4), Article 042302. https://doi.org/10.1103/PhysRevLett.127.042302

JYU authors or editors

Publication details

All authors or editors: ALICE Collaboration

Journal or series: Physical Review Letters

ISSN: 0031-9007

eISSN: 1079-7114

Publication year: 2021

Volume: 127

Issue number: 4

Article number: 042302

Publisher: American Physical Society

Publication country: United States

Publication language: English

DOI: https://doi.org/10.1103/PhysRevLett.127.042302

Publication open access: Openly available

Publication channel open access: Partially open access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/77414

Publication is parallel published: https://arxiv.org/abs/2005.14522

Abstract

A measurement of dielectron production in proton-proton (pp) collisions at √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 mee and pair transverse momentum pT,ee that was previously inaccessible at the LHC. The cross section for dielectron production is studied as a function of mee, pT,ee, and event multiplicity dNch/dη. The expected dielectron rate from hadron decays, called hadronic cocktail, utilizes a parametrization of the measured η/π0 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<0.6 GeV/c2 and for pT,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)±0.34(syst,cocktail) 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.

Keywords: particle physics

Contributing organizations

Ministry reporting: Yes

Reporting Year: 2021

JUFO rating: 3