Test of lepton flavour universality in $W$-boson decays into electrons and $τ$-leptons using $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

ATLAS Collaboration

doi:10.1007/JHEP05(2025)038

paper

Test of lepton flavour universality in $W$ -boson decays into electrons and $τ$ -leptons using $pp$ collisions at $s = 13$ TeV with the ATLAS detector

arXiv:2412.11989 · doi:10.1007/JHEP05(2025)038

Abstract

A measurement of the ratio of the branching fractions, $R_{τ / e} = B (W \to τ ν) / B (W \to e ν)$ , is performed using a sample of $W$ bosons originating from top-quark decays to final states containing $τ$ -leptons or electrons. This measurement uses $pp$ collisions at $s = 13$ TeV, collected by the ATLAS experiment at the Large Hadron Collider during Run 2, corresponding to an integrated luminosity of 140 fb $^{- 1}$ . The $W \to τ ν_{τ}$ (with $τ \to e ν_{e} ν_{τ}$ ) and $W \to e ν_{e}$ decays are distinguished using the differences in the impact parameter distributions and transverse momentum spectra of the electrons. The measured ratio of branching fractions $R_{τ / e} = 0.975 \pm 0.012 (stat.) \pm 0.020 (syst.)$ , is consistent with the Standard Model assumption of lepton flavour universality in $W$ -boson decays.

arXiv comment50 pages in total, author list starting page 33, 8 figures, 4 tables, published on JHEP. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2023-10

Test of lepton flavour universality in W-boson decays into electrons and τ-leptons using pp collisions at s​=13 TeV with the ATLAS detector

Abstract

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Test of lepton flavour universality in $W$ -boson decays into electrons and $τ$ -leptons using $pp$ collisions at $s = 13$ TeV with the ATLAS detector