Evidence for ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_e$ Oscillations from the LSND Experiment at LAMPF

Abstract

A search for ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_e$ oscillations has been conducted at the Los Alamos Meson Physics Facility by using ${\bar{\nu }}_{\mu }$ from ${\mu }^{+}$ decay at rest. The ${\bar{\nu }}_e$ are detected via the reaction ${\bar{\nu }}_{e}p\to e^{+}n$, correlated with a $\gamma$ from $np\to d\gamma$ ($2.2\mathrm{MeV}$). The use of tight cuts to identify $e^{+}$ events with correlated $\gamma$ rays yields 22 events with $e^{+}$ energy between 36 and $60\mathrm{MeV}$ and only $4.6\pm 0.6$ background events. A fit to the $e^{+}$ events between 20 and $60\mathrm{MeV}$ yields a total excess of $51.8_{-16.9}^{+18.7}\pm 8.0$ events. If attributed to ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_e$ oscillations, this corresponds to an oscillation probability of ($0.31_{-0.10}^{+0.11}\pm 0.05$)\%.

4 pages, 3 figures, revtex, psfig. additional information available at http://nu1.lampf.lanl.gov/~lsnd/