Search for Right-Handed Currents in Muon Decay

New limits are reported on right-handed currents, based on precise measurement of the e⁺ spectrum end point in μ⁺ decay. Highly polarized muons from the TRIUMF "surface" beam were stopped in metal foils within a 1.1-T spin-holding longitudinal field or a 70-G spin-precessing transverse field. For the spin-held data, the V-A decay rate vanishes in the beam direction at the end point. Measurement of this rate sets the 90%-confidence limits ξP_μδρ>0.9959 and M(WR)>380 GeV, where WR is the possible righthanded gauge boson.