Leeuw, LerothodiAad, GeorgesAakvaag, Erlend2026-01-212026-01-212025Alpigiani, C. et al. (2025) 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. The journal of high energy physics. [Online] 2025 (5), 38.https://doi.org/10.1007/JHEP05(2025)038https://hdl.handle.net/10566/21790A measurement of the ratio of the branching fractions, Rτ/e = B(W → τν)/B(W → eν), 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 = 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 → τντ (with τ → eνeντ) and W → eνe decays are distinguished using the differences in the impact parameter distributions and transverse momentum spectra of the electrons. The measured ratio of branching fractions Rτ/e = 0.975 ± 0.012 (stat.) ± 0.020 (syst.), is consistent with the Standard Model assumption of lepton flavour universality in W-boson decays.enBranching fractionsElectronsLeptonsFlavour PhysicsHadron-Hadron ScatteringArticle