Evidence for neutrino oscillations from muon decay at rest.

TLDR: In this article, a search for oscillations at rest at the Los Alamos Meson Physics Facility using tight cuts was conducted, and the results showed that the probability that this excess is due entirely to a statistical fluctuation is 4.05%.

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