Search for massive neutrinos in the decayπ→eν

Evidence of massive neutrinos in the ${\ensuremath{\pi}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\nu}$ decay spectrum was sought with the background ${\ensuremath{\pi}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}$ decay chain highly suppressed. Upper limits (90% C.L.) on the neutrino mixing matrix element $|{U}_{ei}{|}^{2}$ in the neutrino mass region $60--129\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ were set at the level of ${10}^{\ensuremath{-}8}$.