Evidence for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_{\mathit{e}}$ Oscillations from the LSND Experiment at the Los Alamos Meson Physics Facility

A search for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillations has been conducted at the Los Alamos Meson Physics Facility by using ${\overline{\nu }}_{\mu }$ from ${\mu }^{+}$ decay at rest. The ${\overline{\nu }}_e$ are detected via the reaction ${\overline{\nu }}_{e}p\to e^{+}n$, correlated with a $\gamma$ from $\mathrm{np}\to d\gamma$ ( $2.2\mathrm{MeV}$). The use of tight cuts to identify $e^{+}$ events with correlated $\gamma$ rays yields 22 events with $e^{+}$ energy between 36 and $60\mathrm{MeV}$ and only $4.6\pm 0.6$ background events. A fit to the $e^{+}$ events between 20 and $60\mathrm{MeV}$ yields a total excess of ${51.0}_{-19.5\mathrm{}}^{+20.2\mathrm{}}\pm 8.0$ events. If attributed to ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillations, this corresponds to an oscillation probability of ( $0.31\pm 0.12\pm 0.05$)%.