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The various experiments on neutrino oscillation evidenced that neutrinos have indeed non-zero masses but cannot tell us the absolute neutrino mass scale. This scale of neutrino masses is very important for understanding the evolution and the structure formation of the universe as well as for nuclear and particle physics beyond the present Standard Model. Complementary to deducing constraints on the sum of all neutrino masses from cosmological observations two different methods to determine the neutrino mass scale in the laboratory are pursued: the search for neutrinoless double $beta$-decay and the direct neutrino mass search by investigating single $beta$-decays or electron captures. The former method is not only sensitive to neutrino masses but also probes the Majorana character of neutrinos and thus lepton number violation with high sensitivity. Currently quite a few experiments with different techniques are being constructed, commissioned or are even running, which aim for a sensitivity on the neutrino mass of {cal O}(100) meV. The principle methods and these experiments will be discussed in this short review.
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This white paper is a condensation of a report by a committee appointed jointly by the Nuclear Science and Physics Divisions at Lawrence Berkeley National Laboratory (LBNL). The goal of this study was to identify the most promising technique(s) for resolving the neutrino mass hierarchy. For the most part, we have relied on calculations and simulations presented by the proponents of the various experiments. We have included evaluations of the opportunities and challenges for these experiments based on what is available already in the literature.
We present an overview of the foundation, evolution, contributions and future prospects of the TEXONO Collaboration and its research programs on neutrino physics and dark matter searches at the Kuo-Sheng Reactor Neutrino Laboratory in Taiwan and, as a founding partner of the CDEX program, at the China Jinping Underground Laboratory in China.
We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest ($K^+ rightarrow mu^+ u_mu$) at the NuMI beamline absorber. These signal $ u_mu$-carbon events are distinguished from primarily pion decay in flight $ u_mu$ and $overline{ u}_mu$ backgrounds produced at the target station and decay pipe using their arrival time and reconstructed muon energy. The significance of the signal observation is at the 3.9$sigma$ level. The muon kinetic energy, neutrino-nucleus energy transfer ($omega=E_ u-E_mu$), and total cross section for these events is extracted. This result is the first known-energy, weak-interaction-only probe of the nucleus to yield a measurement of $omega$ using neutrinos, a quantity thus far only accessible through electron scattering.
We calculate the charged-current cross sections obtained at the T2K off-axis near detector for $ u_mu$-induced events without pions and any number of protons in the final state using transport theory as encoded in the GiBUU model. In a comparison with recent T2K data the strength of the 2p2h multinucleon correlations is determined. Linking this to the isospin (T) of the initial nuclear state, it is found that T=0 leads to a significantly better fit of the recent cross sections obtained by T2K, thus achieving consistency of the 2p2h multi-nucleon correlation contributions between electron-nucleus and neutrino-nucleus reactions.
Neutrino-nucleus elastic scattering ($ u {rm A}_{el}$) provides a unique laboratory to study the quantum-mechanical (QM) coherency effects in electroweak interactions. The deviations of the cross-sections from those of completely coherent systems can be quantitatively characterized through a coherency parameter $alpha ( q^2 )$. The relations between $alpha$ and the underlying nuclear physics in terms of nuclear form factors are derived. The dependence of cross-section on $alpha ( q^2 )$ for the various neutrino sources is presented. The $alpha ( q^2 )$-values are evaluated from the measured data of the COHERENT CsI and Ar experiments. Complete coherency and decoherency conditions are excluded by the CsI data with $p {=} 0.004$ at $q^2 {=} 3.1 {times} 10^{3} ~ {rm MeV^2}$ and with $p {=} 0.016$ at $q^2 {=} 2.3 {times} 10^{3} ~ {rm MeV^2}$, respectively, verifying that both QM superpositions and nuclear many-body effects contribute to $ u {rm A}_{el}$ interactions.
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