0000000000478601
AUTHOR
J. Comfort
Search for heavy neutrinos in → Decay
In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays π+→μ+ν at rest by examining the observed muon energy spectrum for extra peaks in addition to the expected peak for a light neutrino. No evidence for heavy neutrinos was observed. Upper limits were set on the neutrino mixing matrix |Uμi|2 in the neutrino mass region of 15.7–33.8 MeV/c$^{2}$, improving on previous results by an order of magnitude.
Improved search for heavy neutrinos in the decay π→eν
A search for massive neutrinos has been made in the decay π+→e+ν. No evidence was found for extra peaks in the positron energy spectrum indicative of pion decays involving massive neutrinos (π→e+νh). Upper limits (90% C.L.) on the neutrino mixing matrix element |Uei|2 in the neutrino mass region 60–135 MeV/c2 were set and are an order of magnitude improvement over previous results.
Initial results from the PIENU experiment
The pion branching ratio, $R_{\pi } = \frac { {\Gamma }(\pi ^{+} \rightarrow e^{+} \nu _{e} + \pi ^{+}\rightarrow e^{+} \nu _{e} \gamma )}{\Gamma (\pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } + \pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } \gamma )}$ , provides a sensitive test of lepton universality and constraints on many new physics scenarios. The theoretical uncertainty on the Standard Model prediction of R π is 0.02 %, a factor of twenty smaller than the experimental uncertainty. The analysis of a subset of data taken by the PIENU experiment will be presented. The result, R π = (1.2344 ± 0.0023(s t a t) ± 0.0019(s y s t)) ⋅ 10−4 [1], is consistent with the Standard Model prediction and repres…