Improved limits on nuebar emission from mu+ decay
Abstract
We investigated mu+ decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for via the detection reaction p(,e+)n. No signal from LF violating mu+ decays was identified. We extract upper limits of the branching ratio for the LF violating decay mu+ -> e+ compared to the Standard Model (SM) mu+ -> e+ nue numub decay: BR < 0.9(1.7)x10-3 (90%CL) depending on the spectral distribution of characterized by the Michel parameter rho=0.75 (0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which emission from mu+ decay is allowed with considerable strength. The decay μpdeb as source for the signal observed in the LSND experiment can be excluded.
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