The KARMEN limit on ν-barμ → ν-bare oscillations and its implication for the LSND result

The KARMEN experiment is located at the pulsed spallation neutron source ISIS of the Rutherford Appleton Laboratory. In the ISIS beam stop νμ, νe and ν-barμ are produced from the π+-μ+ decay chain at rest with energies up to 52.8 MeV. Besides a very low ν-bare contamination, ISIS stands out for its unique time structure. This allows for a highly sensitive search for ν-barμ→ν-bare-oscillations with the KARMEN detector, a 56 t segmented liquid scintillation calorimeter with very good time, energy and position resolution. Here we present the data taken from Feb. 1997 until Feb. 1999. Since there is no indication for any beam excess, an upper limit for the ν-barμ→ν-bare oscillation is deduced using the Unified Approach based on a maximum likelihood analysis. The result is in line with the data presented previously and is in contradiction to an interpretation of the LSND beam excess as indication for ν-barμ→ν-bare oscillation. A combined statistical analysis of the KARMEN and LSND likelihood functions underlines this