Lepton family number violation is tested by searching for µ + → e + X 0 decays among the 5.8×10 8 positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive X 0 bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic µ + → e + X 0 decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order 10 −5 are obtained for bosons with masses of 13 -80 MeV/c 2 and with different decay asymmetries. For bosons with masses less than 13 MeV/c 2 the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to 5.8 × 10 −5 . This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.
The TWIST Collaboration has completed its measurement of the three muon decay parameters , , and P . This paper describes our determination of , which governs the shape of the overall momentum spectrum, and , which controls the momentum dependence of the parity-violating decay asymmetry. The results are ¼ 0:749 77 AE 0:000 12ðstatÞ AE 0:000 23ðsystÞ and ¼ 0:750 49 AE 0:000 21ðstatÞ AE 0:000 27ðsystÞ. These are consistent with the value of 3=4 given for both parameters in the standard model, and each is over a factor of 10 more precise than the measurements published prior to TWIST. Our final results on , , and P have been incorporated into a new global analysis of all available muon decay data, resulting in improved modelindependent constraints on the possible weak interactions of right-handed particles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.