Results on ${\nu }_{\mu }\to {\nu }_e$ oscillations from pion decay in flight neutrinos

A search for ${\nu }_{\mu }\to {\nu }_e$ oscillations has been conducted at the Los Alamos Meson Physics Facility using ${\nu }_{\mu }$ from ${\pi }^{+}$ decay in flight. An excess in the number of beam-related events from the ${\nu }_e\overrightarrow{C}{e}^{-}X$ inclusive reaction is observed. The excess is too large to be explained by normal ${\nu }_e$ contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of $(2.6\mathrm{}\pm 1.0\pm 0.5)\times {10}^{-3}$ is consistent with the previously reported ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillation evidence from LSND.