Results from the KARMEN νμ → ν e neutrino oscillation search

Abstract

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides ν μ 's, ν e 's and ν μ 's in equal intensities from the π + -μ + decay at rest (DAR). The oscillation channel ν μ → ν e is investigated in the appearance mode with a 56 t liquid scintillation calorimeter at a mean distance of 17.7m from the ν -source looking for p( ν e , e + )n reactions. In the data collected through 1997 and 1998 no potential oscillation event was observed. Using a unified approach to small signals as recommended by the PDG, this leads to an upper limit for the mixing angle of sin 2 (2Θ) < 1.3 · 10 −3 (90% CL) at large Δ m 2 . The excluded area in (sin 2 (2Θ),Δ m 2 ) covers almost entirely the favored region defined by the LSND ν μ → ν e evidence.