Measurement of the $\tau$ branching fractions into leptons

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 ̄ μ ν 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) .

electron positron: colliding beams
electron positron: annihilation
Z0: electroproduction
tau: pair production
tau: leptonic decay
tau: branching ratio
muon: coupling constant
electron: coupling constant
charged current
coupling constant: ratio

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