Measurement of the tau branching fractions into leptons

Abstract

Using data collected with the L3 detector near the Z resonance, corresponding to an integrated luminosity of 150 pb −1, the branching fractions of the tau lepton into electron and muon are measured to be B(τ→ e ν ̄ e ν τ)=(17.806±0.104 ( stat.)±0.076 ( syst.))% , B(τ→μ ν ̄ μν τ)=(17.342±0.110 ( stat.)±0.067 ( syst.))% . From these results the ratio of the charged current coupling constants of the muon and the electron is determined to be g μ / g e=1.0007±0.0051. Assuming electron-muon universality, the Fermi constant is measured in tau lepton decays as G F =(1.1616±0.0058)×10 −5 GeV −2. Furthermore, the coupling constant of the strong interaction at the tau mass scale is obtained as α s(m τ 2)=0.322±0.009 (exp.)±0.015 (theory) .