Evidence for Neutrino Oscillations from Muon Decay at Rest

A search for {bar {nu}}{sub {mu}}{r_arrow}{bar {nu}}{sub {ital e}} oscillations has been conducted at the Los Alamos Meson Physics Facility using {bar {nu}}{sub {mu}} from {mu}{sup +} decay at rest. The {bar {nu}}{sub {ital e}} are detected via the reaction {bar {nu}}{sub {ital ep}}{r_arrow}{ital e}{sup +}{ital n}, correlated with the 2.2 MeV {gamma} from {ital np}{r_arrow}{ital d}{gamma}. The use of tight cuts to identify {ital e}{sup +} events with correlated {gamma} rays yields 22 events with {ital e}{sup +} energy between 36 and 60MeV and only 4.6{plus_minus}0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1{times}10{sup {minus}8}. A {chi}{sup 2} fit to the entire {ital e}{sup +} sample results in a total excess of 51.0{sub {minus}19.5}{sup +20.2}{plus_minus}8.0 events with {ital e}{sup +} energy between 20 and 60MeV. If attributed to {bar {nu}}{sub {mu}}{r_arrow}{bar {nu}}{sub {ital e}} oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31{plus_minus}0.12{plus_minus}0.05){percent}. {copyright} {ital 1996 The American Physical Society.}