Search for right-handed currents in muon decay

Limits are reported on charged right-handed currents, based on precise measurement of the end-point e⁺ spectrum in μ⁺ decay. Highly polarized μ⁺ from a TRIUMF ``surface'' muon beam were stopped in pure metal foil and liquid-He targets selected to minimize depolarization effects. In the stopping target region either a spin-precessing transverse field (70 or 110 G) or a spin-holding longitudinal field (0.3 or 1.1 T) was applied. Data collected with the spin-precessing field were used for the momentum calibration of the spectrometer. The spin-held data were used to measure the relative e⁺ rate at the momentum end point in a direction opposite to the μ⁺ spin. In terms of the standard muon-decay parameters this rate is given by (1-{ξ}P_μ{δ}/{ρ}) where P_μ is the muon polarization. The combined 90% confidence lower limit from the analysis presented in this paper and our earlier analysis of the spin-precessed data by means of the muon-spin-rotation ({μ}SR) technique is {ξ}P_μ{δ}/{ρ}>0.9975. For models with manifest left-right symmetry and massless neutrinos this result implies the 90% confidence limits m(W₂)>432 GeV/c² and -0.050<{ζ}<0.035, where W₂ is the predominantly right-handed boson and {ζ} is the left-right mixing angle. Limits are also deduced on the ν_μL mass and helicity in π⁺ decay, non-(V-A) couplings in helicity projection form, the mass scale of composite leptons, and the branching ratio for {μ}{→}e+f where f (familon) is the neutral massless Nambu-Goldstone boson associated with flavor-symmetry breaking.