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A problem, whether a neutrino-antineutrino transition could be responsible for the muon neutrino deficit found in underground experiments (Super-Kamiokande, MACRO, Soudan 2) and in the accelerator long-baseline K2K experiment, is discussed in this paper. The intention of the work is not consideration of concrete models for muon neutrino-antineutrino transition but a desire to attract an attention to another possibility of understanding the nature of the measured muon neutrino deficit in neutrino experiments.
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We present a complete update of the analysis of electron neutrino and antineutrino disappearance experiments in terms of neutrino oscillations in the framework of 3+1 neutrino mixing, taking into account the Gallium anomaly, the reactor anomaly, solar neutrino data and nu_e-C scattering data. We discuss the implications of a recent 71Ga(3He,3H)71Ge measurement which give information on the neutrino cross section in Gallium experiments. We discuss the solar bound on active-sterile mixing and present our numerical results. We discuss the connection between the results of the fit of neutrino oscillation data and the heavy neutrino mass effects in beta-decay experiments (considering new Mainz data) and neutrinoless double-beta decay experiments (considering the recent EXO results).
We present a new one-dimensional calculation of low and intermediate energy atmospheric muon and neutrino fluxes, using up-to-date data on primary cosmic rays and hadronic interactions. The existing agreement between calculated muon fluxes and the data of the CAPRICE 94 muon experiment provides an evidence in favor of the validity of our description of hadronic interactions and shower development. This also supports our neutrino fluxes which are essentially lower than those used for the standard analyses of the sub-GeV and multi-GeV neutrino induced events in underground detectors.
Neutrino-nucleus $ u Ato u A$ and antineutrino-nucleus $bar u Ato bar u A$ interactions, when the nucleus conserves its integrity, are discussed with coherent (elastic) and incoherent (inelastic) scattering regimes taken into account. In the first regime the nucleus remains in the same quantum state after the scattering and the cross-section depends on the quadratic number of nucleons. In the second regime the nucleus changes its quantum state and the cross-section has an essentially linear dependence on the number of nucleons. The coherent and incoherent cross-sections are driven by a nuclear nucleon form-factor squared $|F|^2$ term and a $(1-|F|^2)$ term, respectively. One has a smooth transition between the regimes of coherent and incoherent (anti)neutrino-nucleus scattering. Due to the neutral current nature these elastic and inelastic processes are indistinguishable if the nucleus recoil energy is only observed. One way to separate the coherent signal from the incoherent one is to register $gamma$ quanta from deexcitation of the nucleus excited during the incoherent scattering. Another way is to use a very low-energy threshold detector and collect data at very low recoil energies, where the incoherent scattering is vanishingly small. In particular, for ${}^{133}text{Cs}$ and neutrino energies of 30--50 MeV the incoherent cross-section is about 15-20% of the coherent one. Therefore, the COHERENT experiment (with ${}^{133}text{Cs}$) has measured the coherent elastic neutrino nucleus scattering (CE$ u$NS) with the inelastic admixture at a level of 15-20%, if the excitation $gamma$ quantum escapes its detection.
We report on $ u_e$ and $bar{ u}_e$ appearance in $ u_mu$ and $bar{ u}_mu$ beams using the full MINOS data sample. The comparison of these $ u_e$ and $bar{ u}_e$ appearance data at a 735 km baseline with $theta_{13}$ measurements by reactor experiments probes $delta$, the $theta_{23}$ octant degeneracy, and the mass hierarchy. This analysis is the first use of this technique and includes the first accelerator long-baseline search for $bar{ u}_murightarrowbar{ u}_e$. Our data disfavor 31% (5%) of the three-parameter space defined by $delta$, the octant of the $theta_{23}$, and the mass hierarchy at the 68% (90%) C.L. We measure a value of 2sin$^2(2theta_{13})$sin$^2(theta_{23})$ that is consistent with reactor experiments.
We find that magnetic neutrino-electron scattering is unaffected by oscillations for vacuum mixing of Dirac neutrinos with only diagonal moments and for Majorana neutrinos with two flavors. For MSW mixing, these cases again obtain, though the effective moments can depend on the neutrino energy. Thus, e.g., the magnetic moments measured with $bar{ u}_e$ from a reactor and $ u_e$ from the Sun could be different. With minimal assumptions, we find a new limit on $mu_{ u}$ using the 825-days SuperKamiokande solar neutrino data: $|mu_{ u}| le 1.5times 10^{-10} mu_B$ at 90% CL, comparable to the existing reactor limit.
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