No abstract available

[en] The puma model on the basis of the Lorentz and CPT violation may bring an economical interpretation to the conventional neutrinos oscillation and part of the anomalous oscillations. We study the effect of the perturbation to the puma model. In the case of the first-order perturbation which keeps the (23) interchange symmetry, the mixing matrix element U_e3 is always zero. The nonzero mixing matrix element U_e3 is obtained in the second-order perturbation that breaks the (23) interchange symmetry. (authors)

[en] The LSND signal for ν-bar_μ→ν-bar_e oscillations has prompted supposition that there may be a fourth light neutrino or that CPT is violated. Neither explanation provides a good fit to all existing neutrino data. We examine the even more speculative possibility that a four-neutrino model with CPT violation can explain the LSND effect and remain consistent with all other data. We find that models with a 3+1 mass structure in the neutrino sector are viable; a 2+2 structure is permitted only in the antineutrino sector

No abstract available

[en] The MiniBooNE experiment was designed to perform a search for ν_μ → ν_e oscillations in a region of Δm² and sin² 2θ very different from that allowed by standard, three-neutrino oscillations, as determined by solar and atmospheric neutrino experiments. This search was motivated by the LSND experimental observation of an excess of (bar ν)_e events in a (bar ν)_μ beam which was found compatible with two-neutrino oscillations at Δm² ∼ 1 eV² and sin² 2θ < 1%. If confirmed, such oscillation signature could be attributed to the existence of a light, mostly-sterile neutrino, containing small admixtures of weak neutrino eigenstates. In addition to a search for ν_μ → ν_e oscillations, MiniBooNE has also performed a search for (bar ν)_μ → (bar ν)_e oscillations, which provides a test of the LSND two-neutrino oscillation interpretation that is independent of CP or CPT violation assumptions. This dissertation presents the MiniBooNE ν_μ → ν_e and (bar ν)_μ → (bar ν)_e analyses and results, with emphasis on the latter. While the neutrino search excludes the two-neutrino oscillation interpretation of LSND at 98% C.L., the antineutrino search shows an excess of events which is in agreement with the two-neutrino (bar ν)_μ → (bar ν)_e oscillation interpretation of LSND, and excludes the no oscillations hypothesis at 96% C.L. Even though the neutrino and antineutrino oscillation results from MiniBooNE disagree under the single sterile neutrino oscillation hypothesis, a simple extension to the model to include additional sterile neutrino states and the possibility of CP violation allows for differences between neutrino and antineutrino oscillation signatures. In view of that, the viability of oscillation models with one or two sterile neutrinos is investigated in global fits to MiniBooNE and LSND data, with and without constraints from other oscillation experiments with similar sensitivities to those models. A general search for new physics scenarios which would lead to effective non-unitarity of the standard 3 x 3 neutrino mixing matrix, or mixing freedom, is also performed using neutrino and antineutrino data available from MiniBooNE.

[en] The LSND experimental at Los Alamos has conducted a search for ν-bar_μ → ν-bar_e oscillations using ν-bar_μ from μ⁺ decay at rest. The ν-bar_e are detected via the reaction ν-bar_ep → e⁺n, correlated with the 2.2-MeV γ from np → dγ. The use of tight cuts to identify e⁺ events with correlated γ rays yields 22 events with e⁺ energy between 36 and 60 MeV and only 4.6 ± 0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1 x 10^-8. A χ² fit to the entire e⁺ sample results in a total excess of 51.8 ^+18.7_16.9 ±8.0 events with e⁺ energy between 20 and 60 MeV. If attributed to ν-bar_μ-bar → ν-bar_e oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31±0.12±0.05). (author)

[en] A calculation of the atmospheric high-energy muon neutrino spectra and zenith-angle distributions is performed for two primary spectrum parameterizations (by Gaisser and Honda and by Zatsepin and Sokolskaya) with the use of QGSJET-II-03 and SIBYLL 2.1 hadronic models. A comparison of the zenith angle-averaged muon neutrino spectrum with the data of Frejus, AMANDA-II, and IceCube40 experiments makes it clear that, even at energies above 100 TeV, the prompt neutrino contribution is not apparent because of the considerable uncertainties of the experimental data in the high-energy region.

[en] The search for neutrino oscillations is the most sensitive method to probe whether neutrinos are massive. The Karlsruhe Rutherford Medium Energy Neutrino experiment searches for anti ν_μ→ anti ν_e oscillations in the appearance mode. Within data collected from February 1997 through March 2000, 11 candidate events have been reduced with an expected background of 12.3 ± 0.3 events. Including spectral information, an oscillation probability of P(anti ν_μ→ anti ν_e)>0.65 x 10^-3 for large neutrino mass differences is excluded at 90% confidence. This result is in contrast to the reported evidence by the Los Alamos LSND experiment. We introduce the phenomenon and experimental status of neutrino oscillations, present the KARMEN experimental configuration and physical results and discuss their implications on the LSND evidence. (orig.)

[en] KARMEN, the Karlsruhe-Rutherford Medium Energy Neutrinoexperiment at the pulsed spallation neutron facility ISIS uses the beam stop neutrinos ν_μ, ν_e and anti ν_μ from π⁺ and μ⁺ decay at r search for neutrino oscillations in the appearance channels anti ν_μ → anti ν_e and anti ν_μ → anti ν_e. The signature for both oscillations is based on charged current neutrino nuclear interaction spectroscopy in a high resolution 56t liquid scintillator calorimeter. This report describes the results based on data acquired from June 1990 to August 1995. (orig.)

[en] Do neutrinos play a central role in the understanding of the differences between matter and antimatter? New results of an experiment in Japan confirm the suspicion.