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-ξP/sub μ/δ/rho) where P/sub 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 (μSR) technique is ξP/sub μ/δ/rho>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<zeta<0.035, where W2 is the predominantly right-handed boson and zeta is the left-right mixing angle