Results on ν μ →ν e oscillations from pion decay in flight neutrinos

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