15 research outputs found
Improved limits on nuebar emission from mu+ decay
We investigated mu+ decays at rest produced at the ISIS beam stop target.
Lepton flavor (LF) conservation has been tested by searching for \nueb via the
detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays
was identified. We extract upper limits of the branching ratio for the LF
violating decay mu+ -> e+ \nueb \nu compared to the Standard Model (SM) mu+ ->
e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral
distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0).
These results improve earlier limits by one order of magnitude and restrict
extensions of the SM in which \nueb emission from mu+ decay is allowed with
considerable strength. The decay \mupdeb as source for the \nueb signal
observed in the LSND experiment can be excluded.Comment: 10 pages, including 1 figure, 1 tabl
KARMEN Limits on ν<sub>e</sub> -> ν<sub>τ</sub> oscillations in 2-ν and 3-ν mixing schemes
The 56 tonne 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->x. The nu_e emitted in mu+
decay at rest are detected with spectroscopic quality via the exclusive charged
current reaction 12-C(nu_e,e-)12-N_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 allow 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 12-C(nu_e,e-)12-N_g.s. to neutral current events
12-C(nu,nu')12-C* provides additional information in the oscillation channel
nu_e->x . All three analysis methods show no evidence for oscillations. For the
nu_e->nu_tau channel 90%CL limits of sin^2(2t)100eV^2 and
dm^2<0.77eV^2 for maximal mixing in a simple 2 flavor oscillation formalism are
derived. A complete 3 flavor analysis of the experimental data from five years
of measurement with respect to nu_enu_tau and nu_enu_mu mixing is
presented.Comment: 20 pages including 13 figures, submitted to Phys.Rev.