A measurement of the tau to mu nu nu branching ratio

TL;DR

This paper reports a precise measurement of the tau to mu nu nu branching ratio using OPAL data, testing lepton universality and setting limits on charged Higgs boson mass within the Standard Model and MSSM.

Contribution

It provides a new, precise measurement of the tau to mu nu nu branching ratio and uses it to test lepton universality and constrain charged Higgs boson mass.

Findings

Branching ratio B(tau->mu nu nu) = 0.1734 +/- 0.0010

Lepton coupling ratios g(mu)/g(e) and g(tau)/g(e) consistent with unity

Charged Higgs mass limit > 1.30 tan(beta)

Abstract

The tau -> mu nu nu branching ratio has been measured using data collected from 1990 to 1995 by the OPAL detector at the LEP collider. The resulting value of B(tau->mu nu nu) = 0.1734 +/- 0.0009(stat) +/- 0.0005(syst) has been used in conjunction with other OPAL measurements to test lepton universality, yielding the coupling constant ratios g(mu)/g(e) = 1.0005 +/- 0.0043 and g(tau)/g(e) = 1.0031 +/- 0.0047, in good agreement with the Standard Model prediction of unity, and also to determine a value for the Michel parameter eta = 0.004 +/- 0.036. This is subsequently used to find a model-dependent limit of the mass for the charged Higgs boson, m(Higgs) > 1.30 tan(beta), in the Minimal Supersymmetric Standard Model.