Search

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.

A search for ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ oscillations has been conducted with the LSND apparatus using ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ from ${\ensuremath{\pi}}^{+}$ decay in flight. Two analyses observe a total of 40 beam-on high-energy (60--200 MeV) electron events consistent with the ${\ensuremath{\nu}}_{e}\mathrm{C}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}X$ inclusive reaction. This number is significantly above the $21.9\ifmmode\pm\else\textpm\fi{}2.1$ events expected from the ${\ensuremath{\nu}}_{e}$ contamination in the beam and the beam-off background. 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.

Charged current scattering of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ on ${}^{12}\mathrm{C}$ has been studied using a ${\ensuremath{\pi}}^{+}$ decay-in-flight ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ beam at the Los Alamos Meson Physics Facility. A sample of 56.8 $\ifmmode\pm\else\textpm\fi{}9.6$ events satisfying criteria for the exclusive reaction ${}^{12}{\mathrm{C}(\mathrm{\ensuremath{\nu}}}_{\mathrm{\ensuremath{\mu}}}{,\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}{)}^{12}{\mathrm{N}}_{\mathrm{g}.\mathrm{s}.}$ was obtained using a large liquid scintillator neutrino detector. The observed flux-averaged cross section $(6.6\ifmmode\pm\else\textpm\fi{}1.0\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}41}{\mathrm{cm}}^{2}$ agrees well with reliable theoretical expectations. A measurement was also obtained for the inclusive cross section to all accessible ${}^{12}\mathrm{N}$ states ${}^{12}\mathrm{C}({\ensuremath{\nu}}_{\ensuremath{\mu}},{\ensuremath{\mu}}^{\ensuremath{-}})X.$ This flux-averaged cross section is $(11.2\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}1.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}40}{\mathrm{cm}}^{2},$ which is approximately half of that given by a recent continuum random-phase approximation calculation.

A search for nu_bar_mu to nu_bar_e oscillations has been conducted at the Los Alamos Meson Physics Facility using nu_bar_mu from mu+ decay at rest. The nu_bar_e are detected via the reaction (nu_bar_e,p) -> (e+,n), correlated with the 2.2 MeV gamma from (n,p) -> (d,gamma). The use of tight cuts to identify e+ events with correlated gamma rays yields 22 events with 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 4.1E-08. A chi^2 fit to the entire e+ sample results in a total excess of 51.8 (+18.7) (-16.9) (+/- 8.0) events with e+ energy between 20 and 60 MeV. If attributed to nu_bar_mu -> nu_bar_e oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of 0.0031 (+0.0011) (-0.0010) (+/- 0.0005)., 57 pages, 34 figures, revtex, additional information available at http://nu1.lampf.lanl.gov/~lsnd/

A search for ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ oscillations has been conducted at the Los Alamos Meson Physics Facility by using ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ from ${\ensuremath{\mu}}^{+}$ decay at rest. The ${\overline{\ensuremath{\nu}}}_{e}$ are detected via the reaction ${\overline{\ensuremath{\nu}}}_{e}p\ensuremath{\rightarrow}{e}^{+}n$, correlated with a $\ensuremath{\gamma}$ from $\mathrm{np}\ensuremath{\rightarrow}d\ensuremath{\gamma}$ ( $2.2\mathrm{MeV}$). The use of tight cuts to identify ${e}^{+}$ events with correlated $\ensuremath{\gamma}$ rays yields 22 events with ${e}^{+}$ energy between 36 and $60\mathrm{MeV}$ and only $4.6\ifmmode\pm\else\textpm\fi{}0.6$ background events. A fit to the ${e}^{+}$ events between 20 and $60\mathrm{MeV}$ yields a total excess of ${51.0}_{\ensuremath{-}19.5}^{+20.2}\ifmmode\pm\else\textpm\fi{}8.0$ events. If attributed to ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ oscillations, this corresponds to an oscillation probability of ( $0.31\ifmmode\pm\else\textpm\fi{}0.12\ifmmode\pm\else\textpm\fi{}0.05$)%.

A search for ${\overline{\ensuremath{\nu}}}_{e}$'s in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m behind the Los Alamos Meson Physics Facility beam stop. The ${\overline{\ensuremath{\nu}}}_{e}$ are detected via ${\overline{\ensuremath{\nu}}}_{e}p\ensuremath{\rightarrow}{e}^{+}n$ with ${e}^{+}$ energy between 36 and $60\mathrm{MeV}$, followed by a $\ensuremath{\gamma}$ ray from $\mathrm{np}\ensuremath{\rightarrow}d\ensuremath{\gamma}$ ( $2.2\mathrm{MeV}$). Using strict cuts to identify $\ensuremath{\gamma}$ rays correlated with ${e}^{+}$ yields 9 events with only $2.1\ifmmode\pm\else\textpm\fi{}0.3$ background expected. A likelihood fit to the entire ${e}^{+}$ sample results in a total excess of ${16.4}_{\ensuremath{-}8.9}^{+9.7}\ifmmode\pm\else\textpm\fi{}3.3$ events. If attributed to ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}$ oscillations, this corresponds to an oscillation probability of ( ${0.34}_{\ensuremath{-}0.18}^{+0.20}\ifmmode\pm\else\textpm\fi{}0.07$)%.