Muon Decay: Measurement of the Transverse Polarization of the Decay Positrons and its Implications for the Fermi Coupling Constant and Time Reversal Invariance

The two transverse polarization components P_T₁ and P_T₂ of the e⁺ from the decay of polarized μ⁺ have been measured as a function of the e⁺ energy. Their energy averaged values are ⟨P_T₁⟩=(6.3±7.7±3.4)×10^-3 and ⟨P_T₂⟩=(-3.7±7.7±3.4)×10^-3. From the energy dependence of P_T₁ and P_T₂ the decay parameters η,η^'' and α^'/A,β^'/A are derived, respectively. Assuming only one additional coupling besides the dominant V-A interaction one gets improved limits on η, β^'/A, and the scalar coupling constant gRRS: η=(-2.1±7.0±1.0)×10^-3, β^'/A=(-1.3±3.5±0.6)×10^-3, RegRRS=(-4.2±14.0±2.0)×10^-3, and ImgRRS=(5.2±14.0±2.4)×10^-3.