Candidate Events in a Search for Muon Antineutrino to Electron Antineutrino Oscillations

A search for $\text{nuebar}$’s in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m from a proton beam dump at LAMPF. A $\text{nuebar}$ signal was detected via the reaction $\text{nuebar}p\to e^{+}n$ with $e^{+}$ energy between 36 and $60\text{mev}$, followed by a $\gamma$ from $np\to d\gamma$ ($2.2\text{mev}$). Using strict cuts to identify $\gamma$’s correlated with positrons results in a signal of 9 events, with an expected background of $2.1\pm 0.3$. A likelihood fit to the entire $e^{+}$ sample yields a total excess of $16.4^{+9.7}{-8.9}\pm 3.3$ events, where the second uncertainty is systematic. If this excess is attributed to neutrino oscillations of the type $\text{numubar}\to \text{nuebar}$, it corresponds to an oscillation probability of ($0.34^{+0.20}{-0.18}\pm 0.07$)%.