Abstract
The τ−→μ−ν̄μντ 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(τ−→μ−ν̄μντ)=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 gμ/ge=1.0005±0.0044 and gτ/ge=1.0031±0.0048, in good agreement with the Standard Model prediction of unity. A value for the Michel parameter η=0.004±0.037 has also been determined and used to find a limit for the mass of the charged Higgs boson, mH±>1.28tanβ, in the Minimal Supersymmetric Standard Model.
Highlights
IntroductionThe e+e− → (e+e−) μ+μ− contribution in the τ − → μ−νμντ sample was evaluated by fitting the Monte Carlo distribution of the acollinearity angle, θacol, to that of the data, where the acollinearity criterion in the τ +τ − selection which requires that θacol < 15◦ has been relaxed, and ptot is required to be less than 20 GeV/c, as shown in Figure 4 (b)
Precise measurements of the leptonic decays of τ leptons provide a means of stringently testing various aspects of the Standard Model
OPAL data collected at energies near the Z0 peak have been used to determine the τ − → μ−νμντ branching ratio, which is found to be
Summary
The e+e− → (e+e−) μ+μ− contribution in the τ − → μ−νμντ sample was evaluated by fitting the Monte Carlo distribution of the acollinearity angle, θacol, to that of the data, where the acollinearity criterion in the τ +τ − selection which requires that θacol < 15◦ has been relaxed, and ptot is required to be less than 20 GeV/c, as shown in Figure 4 (b). This resulted in a fractional background estimate of 0.0052 ± 0.0026.
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