arXiv subjects

C. Ruf

Publications and source records attributed to C. Ruf.

4 recordsLinked to original sources

arXiv2003

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 νcompared 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.

hep-ex↗

arXiv2002

Upper limits for neutrino oscillations muon-antineutrino to electron-antineutrino from muon decay at rest

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

hep-ex↗

arXiv1998

Measurement of the energy spectrum of ν_e from muon decay and implications for the Lorentz structure of the weak interaction

The KARMEN experiment uses the reaction 12C(ν_e,e-)12N to measure the energy distribution of ν_e emitted in muon decay at rest. The ν_e analog ω_l of the famous Michel parameter ρhas been derived from a maximum-likelihood analysis of events near the kinematic end point, E_max. The result, ω_l = (2.7^{+3.8}_{-3.3}\pm 3.1) * 10^{-2}, is in good agreement with the standard model prediction ω_l= 0. We deduce a 90% confidence upper limit of ω_l <= 0.113, which corresponds to a limit of |g^S_RL + 2 g^T_RL| <= 0.78 on the interference term between scalar and tensor coupling constants.

hep-ex↗

arXiv1998

KARMEN Limits on nu_e -> nu_tau Oscillations in 2-neutrino and 3-neutrino 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)<0.338 for dm^2>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_e<->nu_tau and nu_e<->nu_mu mixing is presented.

hep-ex↗