KARMEN-Upgrade: Status and first results

Abstract KARMEN, the Karlsruhe-Rutherford Medium Energy Neutrinoexperiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos ν μ , ν e and ν μ from π + and μ + decay at rest to search for neutrino oscillations in the appearance channels ν μ → ν e and ν μ → ν e . The signature for both oscillations is based on charged current neutrino nuclear interaction spectroscopy in a high resolution 56 t liquid scintillator calorimeter. The detector system has been upgraded with an additional veto layer during 1996 to eliminate cosmogenic background. This report describes results for the oscillation channel ν μ → ν e based on data acquired from June 1990 to August 1995 and the first data of 1997 with the new veto system in operation.