Evidence for neutrino oscillations from muon decay at rest

A search for ν${\mathrm{¯}}_{\mathrm{\mu }}$→ν${\mathrm{¯}}_{\mathit{e}}$ oscillations has been conducted at the Los Alamos Meson Physics Facility using ν${\mathrm{¯}}_{\mathrm{\mu }}$ from ${\mathrm{\mu }}^{+}$ decay at rest. The ν${\mathrm{¯}}_{\mathit{e}}$ are detected via the reaction ν${\mathrm{¯}}_{\mathit{ep}}$→${\mathit{e}}^{+}$n, correlated with the 2.2 MeV γ from np→dγ. The use of tight cuts to identify ${\mathit{e}}^{+}$ events with correlated γ rays yields 22 events with ${\mathit{e}}^{+}$ energy between 36 and 60 MeV and only 4.6±0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1×${10}^{\mathrm{-}8}$. A ${\mathrm{\chi }}^2$ fit to the entire ${\mathit{e}}^{+}$ sample results in a total excess of 51.$0_{\mathrm{-}19.5}^{+20.2\mathrm{}}$±8.0 events with ${\mathit{e}}^{+}$ energy between 20 and 60 MeV. If attributed to ν${\mathrm{¯}}_{\mathrm{\mu }}$→ν${\mathrm{¯}}_{\mathit{e}}$ oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31±0.12±0.05)%. © 1996 The American Physical Society.