Measurement of the Tau Branching Fractions into Leptons

TL;DR

This paper measures tau lepton decay branching fractions into electrons and muons using data from the L3 detector, and derives fundamental constants and coupling ratios, providing tests of lepton universality and strong interaction at the tau mass scale.

Contribution

It provides precise measurements of tau decay branching fractions and fundamental constants, testing lepton universality and strong interaction coupling at the tau mass scale.

Findings

Branching fractions: B(tau->e nu nu) = (17.806 +- 0.104 +- 0.076)%

Branching fractions: B(tau->mu nu nu) = (17.342 +- 0.110 +- 0.067)%

Coupling constant ratio: g_mu/g_e = 1.0007 +- 0.0051

Abstract

Using data collected with the L3 detector near the Z resonance, corresponding to an integrated luminosity of 150pb-1, the branching fractions of the tau lepton into electron and muon are measured to be B(tau->e nu nu) = (17.806 +- 0.104 (stat.) +- 0.076 (syst.)) %, B(tau->mu nu nu) = (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_mu/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 alpha_s(m_tau^2) = 0.322 +- 0.009 (exp.) +- 0.015 (theory).