The problem of the spin of the proton and elastic neutrino-proton scattering
Talk presented by S.M. Bilenky at the Adriatico Research Conference on "Trends in Collider Spin Physics", ICTP, Trieste, December 1995.
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arXiv subjects
S. M. Bilenky
Publications and source records attributed to S. M. Bilenky.
Status of neutrino mixing
Talk presented at the 7th International Workshop on Neutrino Telescopes, Venezia, February 1996.
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Short-baseline neutrino oscillations and neutrinoless double-beta decay in schemes with an inverted mass spectrum
We have considered short-baseline neutrino oscillations, tritium beta-decay and neutrinoless double-beta decay in two schemes with an inverted mass spectrum and mixing of three and four massive neutrino fields. We have analyzed the results of the latest experiments on the search for oscillations of terrestrial neutrinos and we have discussed the compatibility of the LSND indication in favor of neutrino oscillations with the results of the other experiments. In the framework of the models under consideration, it is shown that the observation of neutrinoless double-beta decay could allow to obtain information about the CP violation in the lepton sector.
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Possible tests of neutrino maximal mixing and comments on matter effects
We show in a simple and general way that matter effects do not contribute to the averaged value of the probabilities of transition of solar $ν_e$'s into other states in the case of maximal mixing of any number of massive neutrinos. We also show that future solar neutrino experiments (Super-Kamiokande and SNO) will allow to test the model with maximal mixing of three massive neutrinos in a way that does not depend on the initial solar neutrino flux.
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Short-baseline neutrino oscillations and neutrinoless double-beta decay in the framework of three neutrino mixing and a mass hierarchy
We have analyzed the results of the latest terrestrial neutrino oscillation experiments in the framework of a model with mixing of three massive neutrinos and a neutrino mass hierarchy ($ m_1 << m_2 << m_3 $). In this model, oscillations of the terrestrial neutrinos are characterized by three parameters, $ Δm^2 = m_3^2 - m_1^2 $ and the squared moduli of the two mixing matrix elements $U_{e3}$ and $U_{\mu3}$. Using the results of disappearance experiments and solar neutrino experiments, it is shown that only two regions of possible values of $|U_{e3}|^2$ and $|U_{\mu3}|^2$ are allowed: I. $|U_{e3}|^2$ and $|U_{\mu3}|^2$ are both small and II. $|U_{e3}|^2$ is small and $|U_{\mu3}|^2$ is large. If the mixing parameters are in the region I, $ ν_μ<-> ν_e $ oscillations are suppressed. In this case the LSND indication in favor of $ ν_μ<-> ν_e $ oscillations is not compatible with the negative results of all other experiments. If the mixing parameters are in the region II, $ ν_e <-> ν_τ$ oscillations are strongly suppressed. If massive neutrinos are Majorana particles, our analysis shows that neutrinoless double-beta decay could be observed in the experiments of the next generation only if the mixing parameters are in the region I.
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On the impossibility to distinguish MSW transitions from vacuum oscillations for neutrino maximal mixing
We show in a simple and general way that MSW resonant transitions for solar neutrinos are not observable in the case of maximal mixing among any number of neutrino generations.
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Neutrino masses and mixing
The status of the problem of neutrino masses and mixing is shortly reviewed. Different schemes of mixing of (Dirac or Majorana) massive neutrinos are considered. The theory of neutrino oscillations in vacuum and in matter is presented. Existing indications in favor of neutrino mixing are shortly discussed.
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Neutrino oscillations with three-generation mixings and mass hierarchy
We have analyzed the results of reactor and accelerator neutrino oscillation experiments in a model with mixing of three neutrino fields and a neutrino mass hierarchy. It is shown that $ ν_μ\leftrightarrows ν_e $ oscillations with $ 0.6 \le Δm^2 \le 100 \, \mathrm{eV}^2 $ and amplitude larger than $ 2 \times 10^{-3} $ are not compatible with the existing limits on neutrino oscillations if the non-diagonal elements of the mixing matrix are small. Thus, if the excess of positron events recently observed in the LSND experiment is due to $ \barν_μ\to \barν_e $ oscillations, the mixing in the lepton sector is basically different from the CKM mixing of quarks.
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Possible tests for sterile neutrinos
It is shown that the future SNO and Super-Kamiokande experiments, in which high energy $^8\mathrm{B}$ neutrinos will be detected through the observation of CC, NC and $ν$--$e$ elastic scattering processes, could allow to reveal in a model independent way the presence of sterile neutrinos in the flux of solar neutrinos on the earth.
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Elastic Neutrino-Nucleon and Antineutrino-Nucleon Scattering and Strange Form Factors of the Nucleons
Elastic scattering of neutrinos and antineutrinos on nucleons is considered. It is shown that the measurement of the neutrino-antineutrino asymmetry would allow to obtain model independent informations on the strange axial and vector form factors. The ratio of the magnetic form factors of the proton and neutron, on which the asymmetry depends, is investigated in detail. The asymmetry is calculated under different assumptions on the behavior of the strange vector and axial form factors.
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Neutrino Oscillations in the Framework of Three-Generation Mixings with Mass Hierarchy
We have analyzed the results of reactor and accelerator neutrino oscillation experiments in the framework of a general model with mixing of three neutrino fields and a neutrino mass hierarchy that can accommodate the results of the solar neutrino experiments. It is shown that $ ν_μ\leftrightarrows ν_e $ oscillations with $ 0.6 \le Δm^2 \le 100 \, \mathrm{eV}^2 $ and amplitude larger than $ 2 \times 10^{-3} $ are not compatible with the existing limits on neutrino oscillations if the non-diagonal elements of the mixing matrix $ \left| U_{e3} \right| $ and $ \left| U_{\mu3} \right| $ are small. Thus, if the excess of electron events recently observed in the LSND experiment is due to $ ν_μ\leftrightarrows ν_e $ oscillations, the mixing in the lepton sector is basically different from the CKM mixing of quarks. If this type of mixing is realized in nature, the observation of $ ν_μ\leftrightarrows ν_e $ oscillations would not influence $ ν_μ\leftrightarrows ν_τ$ oscillations that are being searched for in the CHORUS and NOMAD experiments.
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Atmospheric Neutrino Oscillations among Three Neutrino Flavors and Long-Baseline Experiments
Anticipating future long-baseline neutrino experiments to search for neutrino oscillations in various oscillation channels, we have analyzed the atmospheric neutrino data in the framework of a model with mixing of three massive neutrino fields that can accommodate the data of solar neutrino experiments. The oscillations of atmospheric and terrestrial neutrinos are described in this model by three parameters: $ Δm^2 $ and the squared moduli of two elements of the mixing matrix, $ | U_{e3} |^2 $ and $ | U_{\mu3} |^2 $, which determine the amplitudes of oscillations among all active neutrinos. The results of the analysis of the atmospheric neutrino data are presented in the form of allowed regions in the plane of the two parameters oscillation amplitude and $ Δm^2 $ for all oscillation channels to be investigated in the future long-baseline oscillation experiments.
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Some Remarks on Nu(mu)-Nu(e) Oscillations of Terrestrial Neutrinos and Atmospheric Neutrino Oscillations
We present the results of an analysis of the data of reactor and accelerator neutrino oscillation experiments in the framework of a model with mixing of three massive neutrino fields and a neutrino mass hierarchy. The results of the LSND experiment are commented. Taking into account future long-baseline neutrino oscillation experiments, we have also analyzed the atmospheric neutrino data in the framework of the model.
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ARE THERE STERILE NEUTRINOS IN THE FLUX OF SOLAR NEUTRINOS ON THE EARTH?
It is shown that the future SNO and Super-Kamiokande experiments, in which high energy $^8\mathrm{B}$ neutrinos will be detected through the observation of CC, NC and $ν$--$e$ elastic scattering processes, could allow to reveal in a model independent way the presence of sterile neutrinos in the flux of solar neutrinos on the earth. Lower bounds for different averaged values of the probability of transition of solar $ν_e$'s into sterile states and for the total flux of $^8\mathrm{B}$ neutrinos are derived in terms of measurable quantities. The possibilities to reveal the presence of $ν_μ$ and/or $ν_τ$ in the solar neutrino flux on the earth are also considered and the case of transitions of solar $ν_e$'s only into sterile states is discussed. Some numerical results for a simple model with $ν_e$--$ν_s$ mixing are given.
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A MODEL INDEPENDENT APPROACH TO FUTURE SOLAR NEUTRINO EXPERIMENTS
It is shown that from the data of future solar neutrino experiments (SNO and Super-Kamiokande), in which high-energy $^8\mathrm{B}$ neutrinos will be detected, it will be possible in a model independent way: 1) To reveal the presence of sterile neutrinos in the flux of solar neutrinos on the earth; 2) To obtain the initial flux of $^8\mathrm{B}$ $ν_e$'s; 3) To determine the probability of $ν_e$'s to survive as a function of neutrino energy.
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A Model Independent Analysis of Solar Neutrino Data
We present the results of a solar model independent analysis of the existing solar neutrino data in the case of $ν_{e}\toν_{μ(τ)}$ MSW transitions. We considered two cases. In the first case no assumptions on the values of the total fluxes of neutrinos from all reactions have been made. In the second case we constrained the values of the neutrino fluxes within some wide limits that take into account the predictions of the existing Standard Solar Models. We show that in both cases the existing data allow to exclude rather large regions in the plane of the parameters $ Δm^2 $ and $ \sin^2 2θ$.
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A Model Independent Analysis of Solar Neutrino Data
The results of a solar model independent analysis of the existing solar neutrino data under the assumption of MSW transitions in matter or vacuum oscillations (in the cases of $ν_{e}$--$ν_μ(ν_τ)$ and $ν_{e}$--$ν_{\mathrm{S}}$ mixing) are presented. The analysis was done in two cases. In the first case no assumptions on the value of the total fluxes of neutrinos from all reactions has been made. In the second case some boundaries for the values of the neutrino fluxes, that take into account the predictions of different standard solar models, are imposed. It is shown that rather large regions of the parameters $ Δm^2 $ and $ \sin^2 2θ$ are excluded by the existing data. It is also shown that the astrophysical solution of the solar neutrino problem can be excluded only in the case in which limitations on the values of the solar neutrino fluxes are imposed.
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Neutrino Mass and Magnetic Moment from Neutrino-Electron Scattering
We study both the elastic ($νe \rightarrow νe$) and the radiative process ($νe \rightarrow νe γ$) and discuss how these processes can shed light on some current topics in neutrino physics such as a neutrino magnetic moment and neutrino oscillations. The radiative process allows to reach low values of $Q^2$ without the need to operate at very small energies of recoil electrons, a favourable scenario to search for a neutrino magnetic moment. The elastic cross section contains a dynamical zero at $E_ν=m/(4 sin^2θ_{W})$ and forward electrons for the electron antineutrino channel, which is reachable at reactor facilities and accessible after the convolution with the antineutrino spectrum. The implication for lepton flavour changing transitions in that energy region searched for in neutrino oscillation experiments, which combine disappearance and appearance rates, is discussed.
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