• Open Access

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

S. Acharya et al. (A Large Ion Collider Experiment Collaboration)
Phys. Rev. Lett. 127, 042302 – Published 23 July 2021

Abstract

A measurement of dielectron production in proton-proton (pp) collisions at s=13TeV, 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<mee<0.6GeV/c2 and for pT,ee<0.4GeV/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.

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  • Received 15 June 2020
  • Revised 12 April 2021
  • Accepted 8 June 2021

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

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.

© 2021 CERN, for the ALICE Collaboration

Physics Subject Headings (PhySH)

Accelerators & Beams

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Vol. 127, Iss. 4 — 23 July 2021

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