Search for Massive Neutrinos in the Decayπ→eν

The positron spectrum from the decay ${\pi }^{+}\to e^{+}{\nu }_e$ has been examined for evidence of peaks arising from an admixture in the ${\nu }_e$ weak eigenstate of massive neutrinos. Limits on the intensity of such peaks, together with the measured $\pi \to e\nu$ branching ratio, have been used to derive constraints on the neutrino mixing parameters over the range $4 \mathrm{MeV}<m\left(\nu \right)<\mathrm{}135\mathrm{} \mathrm{MeV}$.