Limits on the Neutrino Mass and Mixing Angle from Pion and Lepton Decays
Motivated by a recent rather surprising conclusion based on the 1992 PDG data on the pion, kaon and lepton decays that if three generations of neutrinos are assumed to be massive and mixed, the heaviest neutrino, $ν_3$, could have a mass in the range, $155~\mbox{MeV} \lsim m_3 \lsim 225~\mbox{MeV}$, we have analyzed the latest 1995 data on the leptonic decays of pion, $μ$ and $τ$ with the assumption that three generations of neutrinos are massive and mixed. It is shown that when the radiative corrections are included and the constraint {}from partial decay widths is imposed, the 1995 data are consistent with three massless neutrinos with no mixing. Various limits on the neutrino mass and mixing angle implied by the 1995 data are presented together with a critique of the previous analysis.