Measurement and Analysis of the Rare Muon Decay μ+→ e+νēνμe+e-

The SINDRUM-Spectrometer has measured the kinematical distribution of 7443±148 events of the rare muon decay μ → 3e2ν. The muons were (80 ± 2) % polarized and only the high energy region was investigated. This measurement was a byproduct in the search for the lepton number violating decay μ → 3e. The phase space for the μ → 3e2ν decay was reduced by a factor of ∼5.8 × 10–5 by the following cuts on the charged particle momenta: each momentum transverse to beam direction > 16 MeV/c 36° < θ < 144°, where θ is the azimuthal angle total transverse momentum ≤ 45 MeV/c. Reference [1] gives detailed description of the detector and of the data reduction.