0000000000115046
AUTHOR
S. Ito
Search for heavy neutrinos in \(\pi ^{ + } \to \mu ^{ + }\nu \) decay and status of lepton universality test in the PIENU experiment
International audience; In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays \(\pi ^{ + } \to \mu ^{ + }\nu \). No evidence for extra peak was found in the muon kinetic energy spectrum and 90% confidence level upper limits were set on the neutrino mixing matrix \(|U_{\mu i}|^{2}\) in the mass range of 15.7 to 33.8 MeV/c^2, improving an order of magnitude over previous experiments. Current status of lepton universality test is also reported.
Improved search for two body muon decay μ+→e+XH
Charged lepton flavor violating muon decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{X}_{H}$, where ${X}_{H}$ is a massive neutral boson, was sought by searching for extra peaks in the muon decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ energy spectrum in the ${m}_{{X}_{H}}$ mass region $47.8--95.1\text{ }\text{ }\mathrm{MeV}/{c}^{2}$. No signal was found and 90% confidence level upper limits were set on the branching ratio $\mathrm{\ensuremath{\Gamma}}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{X}_{H})/\mathrm{\ensuremath{\Gamma}}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\nu}\overline{…
Search for heavy neutrinos in → Decay
In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays π+→μ+ν at rest by examining the observed muon energy spectrum for extra peaks in addition to the expected peak for a light neutrino. No evidence for heavy neutrinos was observed. Upper limits were set on the neutrino mixing matrix |Uμi|2 in the neutrino mass region of 15.7–33.8 MeV/c$^{2}$, improving on previous results by an order of magnitude.
SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study
Abstract Background Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18–49, 50–69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results NNVs were more favourable in su…
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.
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…