Evidence for neutrino oscillations from the observation of ${\overline{\nu }}_e$ appearance in a ${\overline{\nu }}_{\mu }$ beam

A search for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using ${\overline{\nu }}_{\mu }$ from ${\mu }^{+}$ decay at rest. A total excess of $87.9\pm 22.4\pm 6.0$ events consistent with ${\overline{\nu }}_e\overrightarrow{p}{e}^{+}n$ scattering was observed above the expected background. This excess corresponds to an oscillation probability of $(0.264\mathrm{}\pm 0.067\pm 0.045)\%,$ which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the $0.2–10\hspace{0.5em}{\mathrm{eV}}^2{/c}^4\hspace{0.5em}\Delta m^2$ range, indicating a neutrino mass greater than $0.4\hspace{0.5em}\mathrm{eV}{/c}^2.$