Improved search for heavy neutrinos in the decay $\pi\rightarrow e\nu$

The PIENU collaboration Aguilar-Arevalo, A. ; Aoki, M. ; Blecher, M. ; et al.
Phys.Rev. D97 (2018) 072012, 2018.
Inspire Record 1642434 DOI 10.17182/hepdata.91133

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.

1 data table

90% C.L. upper limits to |U_{ei}|^2