The asymmetry of positrons in the K++, +e+e decay chain was measured in a search for right-handed weak currents in S=1 semileptonic decay. High-intensity low-background monoenergetic polarized muons of 236 MeV/c momentum resulting from kaon decay at rest were directly extracted from a primary production target which was hit by a proton beam of the KEK 12-GeV proton synchrotron. Muons were stopped in a pure-aluminum plate, and the energy-integrated asymmetry of the decay positrons with respect to the incoming muon direction was determined to high precision. The observed asymmetry yielded P=-0.99960.0030(stat)0.0048(syst) . This result revealed 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.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)