A Measurement of the tau -> mu nu nu Branching Ratio

TL;DR

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

Contribution

It provides a new, precise measurement of the tau to mu nu nu branching ratio and tests lepton universality, also deriving limits on charged Higgs mass in the MSSM.

Findings

Branching ratio B(tau -> mu nu nu) = 0.1734 +- 0.0009 (stat) +- 0.0006 (syst)

Lepton coupling ratios consistent with the Standard Model

Charged Higgs mass limit > 1.25 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) +- 0.0006(syst) has been used in conjunction with other OPAL measurements to test lepton universality, yielding the coupling constant ratios gmu/ge=1.0005+-0.0044 and gt/ge=1.0031+-0.0048, in good agreement with the Standard Model prediction of unity. A value for the Michel parameter eta = 0.004 +- 0.037 has also been determined and used to find a limit for the mass of the charged Higgs boson mH+- > 1.25 tan beta, in the Minimal Supersymmetric Standard Model.