New experimental limits on νe→ντ oscillations in 2-ν and 3-ν mixing schemes

The 56 ton high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel nu(e)-nu(x). The nu(e) emitted in mu(+) decay at rest are detected with spectroscopic quality via the exclusive charged current reaction C-12(nu(e),e(-))N-12(g.s.) almost free of background. Analysis of the spectral shape of e(-) from the nu(e)-induced reaction as well as a measurement of the absolute nu(e) flux allows one to investigate oscillations of the type nu(e) --> nu(tau) and nu(e) --> nu(mu). The flux-independent ratio R-CC/NC of charged current events C-12(nu(e) , e(-))N-12(g.s.) to neutral current,events C-12(nu,nu')C-12* provides additional information in the oscillation channel nu(e) --> v(tau). All three analysis methods show no evidence for oscillations. For the nu(e) --> nu(tau) channel 90% confidence limits of sin(2)(2 Theta)<0.338 for Delta m(2) greater than or equal to 100 eV(2)/c(4) and Delta m(2)<0.77 eV(2)/c(4) for maximal mixing in a simple two-flavor oscillation formalism are derived. A complete three-flavor analysis of the experimental data from 5 years of measurement with respect to nu(e) <-> nu(tau) nu <-> nu(mu) mixing is presented.