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

A measurement of the ratio of the branching fractions, R-tau/e = B(W -> tau nu)/B(W -> e nu), is performed using a sample of W bosons originating from top-quark decays to final states containing tau-leptons or electrons. This measurement uses pp collisions at root 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 -> tau nu(tau) (with tau -> e nu(e)nu(tau)) and W -> e nu(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-tau/e = 0.975 +/- 0.012 (stat.) +/- 0.020 (syst.), is consistent with the Standard Model assumption of lepton flavour universality in W-boson decays.