Search for Right-Handed Currents in Muon Decay

Abstract

New limits are reported on right-handed currents, based on precise measurement of the ${e}^{+}$ spectrum end point in ${\ensuremath{\mu}}^{+}$ 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 $V\ensuremath{-}A$ decay rate vanishes in the beam direction at the end point. Measurement of this rate sets the 90%-confidence limits $\frac{\ensuremath{\xi}{P}_{\ensuremath{\mu}}\ensuremath{\delta}}{\ensuremath{\rho}}>0.9959$ and $M({W}_{R})>380$ GeV, where ${W}_{R}$ is the possible righthanded gauge boson.