The KARMEN2 quest for (ν)over-barμ→(ν)over-bare oscillations

Neutrino oscillations are a sensitive method to probe neutrinos for masses. The neutrino experiment KARMEN is searching for (ν) over bar (mu) --> (ν) over bar (e), oscillations at the neutron spallation source ISIS by using (ν) over bar (e) from the decay at rest mu(+) --> e(+) + nu(e) + <(nu)over bar>(mu). The appearance of an electron-antineurino <(nu)over bar>(e), is detected via the inverse beta reaction p <(nu)over bar>(e) , e(+) ) n on the free protons of the detector, which is basically a segmented tank with a volume of 65 m(3) , filled with liquid scintillator. Analyzing the data set recorded from Feb.1997 up to March 2000 the search of (ν) over tilde (e) 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 sin(2)(2theta) < 1.3 (.) 10(-3) for large Deltam(2) > 100 eV(2) and Delta(m)(2) < 0.049 eV(2) for sin (2theta) = 1. Due to these results the parameter space of the claimed <(nu)over bar>(mu) --> <(nu)over bar>(e) oscillations by the LSND experiment is strongly restricted and thus the LSND result is not confirmed.