The Karmen2 quest for νμ → νe oscillations

Neutrino oscillations are a sensitive method to probe neutrinos for masses. The neutrino experiment KARMEN is searching for νμ → νe oscillations at the neutron spallation source ISIS by using νμ from the decay at rest μ+ → e+ + νe + νμ. The appearance of an electron-antineutrino νe is detected via the inverse beta reaction p (νe, e+) n on the free protons of the detector, which is basically a segmented tank with a volume of 65 m3, filled with liquid scintillator. Analyzing the data set recorded from Feb.1997 up to March 2000 the search of νe appearance yields no hints for neutrino oscillations. Applying a likelihood method to the measured event sample of 11 events (background expectation 12.3 events), we deduce an upper limit of sin2(2Θ) < 1.3 · 10-3 for large δm2 > 100 eV2 and δm2 '' 0.049 eV2 for sin2(2Θ)=1. Due to these results the parameter space of the claim νμ → νe oscillations by the LSND experiment is strongly restricted and thus the LSND result is not confirmed