A search for ${\nu }_{\mu }\to {\nu }_e$ oscillations has been conducted with the LSND apparatus using ${\nu }_{\mu }$ from ${\pi }^{+}$ decay in flight. Two analyses observe a total of 40 beam-on high-energy (60–200 MeV) electron events consistent with the ${\nu }_e\mathrm{C}\to e^{-}X$ inclusive reaction. This number is significantly above the $21.9\pm 2.1$ events expected from the ${\nu }_e$ contamination in the beam and the beam-off background. If interpreted as an oscillation signal, the observed oscillation probability of $(2.6\pm 1.0\pm 0.5)\times {10}^{-3\mathrm{}}$ is consistent with the previously reported ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillation evidence from LSND.

• Received 10 September 1997

DOI:https://doi.org/10.1103/PhysRevLett.81.1774