Search for right-handed currents by means of muon spin rotation

A muon spin rotation (mu SR) technique has been used to place limits on right-handed weak currents in mu(+) decay. A beam of almost 100% polarized surface muons obtained from the TRIUMF M13 beamline was stopped in essentially non-depolarizing 99.99% pure metal foils. The mu(+) spins were precessed by 70-G or 110-G transverse fields. Decay e(+) emitted within 225 mrad of the beam direction and with momenta above 46 MeV/c were momentum-analyzed to 0.2%. Comparison of the mu SR signal amplitude with that expected for (V-A) decay yields an endpoint asymmetry xi P(sub mu)delta/rho 0.9951 with 90% confidence. In the context of manifest left-right symmetric models with massless neutrinos the results imply the 90% confidence limits M(W sub 2) 381 GeV/c(2) and 0.057 zeta 0.044, where W sub 2 is a predominantly right-handed gauge boson and zeta is the left-right mixing angle. Limits on M(W sub 2) for M(nu sub mu R) does not equal 0 are also presented. The endpoint asymmetry is used to deduce limits on the nu sub mu L mass and helicity in pi(+) decay, non-(V-A) couplings in helicity projection form, and the mass scale of composite leptons.