Candidate Events in a Search for ${{\overline{\nu }}_{\mu }\to \overline{\nu }}_{\mathit{e}}$ Oscillations

A search for ${\overline{\nu }}_e$'s in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m behind the Los Alamos Meson Physics Facility beam stop. The ${\overline{\nu }}_e$ are detected via ${\overline{\nu }}_{e}p\to e^{+}n$ with $e^{+}$ energy between 36 and $60\mathrm{MeV}$, followed by a $\gamma$ ray from $\mathrm{np}\to d\gamma$ ( $2.2\mathrm{MeV}$). Using strict cuts to identify $\gamma$ rays correlated with $e^{+}$ yields 9 events with only $2.1\pm 0.3$ background expected. A likelihood fit to the entire $e^{+}$ sample results in a total excess of ${16.4}_{-8.9\mathrm{}}^{+9.7\mathrm{}}\pm 3.3$ events. If attributed to ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillations, this corresponds to an oscillation probability of ( ${0.34}_{-0.18\mathrm{}}^{+0.20\mathrm{}}\pm 0.07$)%.