SEARCH FOR RIGHT-HANDED CURRENTS IN THE DECAY CHAIN OF K-]MU+NU(MU), MU+-]E+NU(E)NU(MU)()

The asymmetry of positrons in the K+ --> mu+nu, mu+ --> e+nu(e)nu(mu)B AR decay chain was measured in a search for right-handed weak currents in DELTAS = 1 semileptonic decay. High-intensity low-background monoe nergetic polarized muons of 236 MeV/c momentum resulting from kaon dec ay at rest were directly extracted from a primary production target wh ich was hit by a proton beam of the KEK 12-GeV proton synchrotron. Muo ns were stopped iu a pure-aluminum plate, and the energy-integrated as ymmetry of the decay positrons with respect to the incoming muon direc tion was determined to high precision. The observed asymmetry yielded xiP(mu) = -0.9996 +/- 0.0030(stat) +/- 0.0048(syst). This result revea led no evidence of right-handed currents in this kaon-decay chain, and set a stringent bound on the mass of the right-handed weak boson.