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

A measurement of the ratio of the branching fractions, $\textit{R}$ = $\textit{B}$($\textit{W}$ → $\textit{τν}$)$\textit{/B}$($\textit{W}$ → $\textit{eν}$), is performed using a sample of $\textit{W}$ bosons originating from top-quark decays to final states containing $\textit{τ}$-leptons or electrons. This measurement uses $\textit{pp}$ 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 . The $\textit{W → τν}$ (with $\textit{τ → eν}$ $\textit{ν}$ ) and $\textit{W → eν}$ decays are distinguished using the differences in the impact parameter distributions and transverse momentum spectra of the electrons. The measured ratio of branching fractions $\textit{R}$ = 0$\textit{.}$975 ± 0$\textit{.}$012 (stat.) ± 0$\textit{.}$020 (syst.), is consistent with the Standard Model assumption of lepton flavour universality in $\textit{W}$-boson decays.