Mass Hierarchy via Mossbauer and Reactor Neutrinos
We show how one could determine the neutrino mass hierarchy with Mossbauer neutrinos and also revisit the question of whether the hierarchy can be determined with reactor neutrinos.
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arXiv subjects
Hiroshi Nunokawa
Publications and source records attributed to Hiroshi Nunokawa.
Determination of the Neutrino Mass Hierarchy via the Phase of the Disappearance Oscillation Probability with a Monochromatic \barν_e Source
The neutrino mass hierarchy can be determined, in principle, by measuring a phase in the disappearance oscillation probability in vacuum, without relying on the matter effect, using a single channel. This phase is not the same for the normal and inverted neutrino mass spectra. In this paper, we give a complete description and physics understanding of the method. The key feature of the method is to detect advancement (normal) or retardation (inverted) of the phase of the atmospheric-scale oscillation relative to the solar-scale oscillation. We then show that this method can be realized with the recently proposed resonant $\barν_{e}$ absorption reaction enhanced by Mössbauer effect. The unique feature of this setup is the ultra-monochromaticity of the observed \barν_{e}'s. Because of this feature the phase advancement or retardation of atmospheric-scale neutrino oscillation is detectable after 20 or more oscillations if the source and the target are made sufficiently compact in size. A quantitative estimate of the sensitivity to mass hierarchy resolution is given. We have also examined how a possible continuation of such experiment can be carried out in order also to achieve high precision (few %) determination of the solar-scale oscillation parameters Δm^2_{21} and θ_{12}.
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Non-Standard Neutrino Physics Probed by Tokai-to-Kamioka-Korea Two-Detector Complex
The discovery potentials of non-standard physics (NSP) which might be possessed by neutrinos are examined by taking a concrete setting of Tokai-to-Kamioka-Korea (T2KK) two detector complex which receives neutrino superbeam from J-PARC. We restrict ourselves into ν_μ and \barν_μ disappearance measurement. We describe here only the non-standard interactions (NSI) of neutrinos with matter and the quantum decoherence. It is shown in some favorable cases T2KK can significantly improve the current bounds on NSP. For NSI, for example, epsilon_{μτ} < 0.03, which is a factor 5 severer than the current one.
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Probing Nonstandard Neutrino Physics by Two Identical Detectors with Different Baselines
The Kamioka-Korea two detector system is a powerful experimental setup for resolving neutrino parameter degeneracies and probing CP violation in neutrino oscillation. In this paper, we study sensitivities of this same setup to several nonstandard neutrino physics such as quantum decoherence, tiny violation of Lorentz symmetry, and nonstandard interactions of neutrinos with matter. In most cases, the Kamioka-Korea two-detector setup is more sensitive than the one-detector setup, except for the Lorentz symmetry violation with CPT violation, and the nonstandard neutrino interactions with matter. It can achieve significant improvement on the current bounds on nonstandard neutrino physics.
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CP Violation and Neutrino Oscillations
We review the basic mechanisms of neutrino mass generation and the corresponding structure of the lepton mixing matrix. We summarize the status of three-neutrino oscillation parameters as determined from current observations, using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest experimental data as of September 2007. We also comment on recent attempts to account for these results and to understand flavour from first principles. We discuss extensively the prospects for probing the strength of CP violation in two near term accelerator neutrino oscillation experiments, T2K and NOvA, as well as possible extensions such as T2KK and a second large off-axis detector near the NOvA detector. We also briefly discuss the possibility of probing the effect of Majorana phases in future neutrinoless double beta decay searches and discuss other implications of leptonic CP violation such as leptogenesis. Finally we comment on the issue of robustness of the current oscillation interpretation and possible ways of probing for non-standard neutrino interactions in precision oscillation studies.
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Resolving the Octant theta(23) Degeneracy by Neutrino Oscillation Experiments
We discuss how and to what extent the degeneracy associated with theta(23), if it's not maximal, can be resolved by future oscillation experiments which utilize conventional neutrino beam from accelerator and/or reactor neutrinos.
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Resolving Eight-Fold Neutrino Parameter Degeneracy by Two Identical Detectors with Different Baselines
We have shown in a previous paper that two identical detectors with each fiducial mass of 0.27 megaton water, one in Kamioka and the other in Korea, which receive the (anti-) muon neutrino beam of 4 MW power from J-PARC facility have potential of determining the neutrino mass hierarchy and discovering CP violation by resolving the degeneracies associated with them. In this paper, we point out that the same setting has capability of resolving the θ_{23} octant degeneracy in region where sin^2 2θ_{23} \lsim 0.97 at 2 standard deviation confidence level even for very small values of θ_{13}. Altogether, it is demonstrated that one can solve all the eight-fold neutrino parameter degeneracies in situ by using the Tokai-to-Kamioka-Korea setting if θ_{13} is within reach by the next generation superbeam experiments. We also prove the property called ``decoupling between the degeneracies'', which is valid to first order in perturbation theory of the earth matter effect, that guarantees approximate independence between analyses to solve any one of the three different type of degeneracies.
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NOvA and T2K: The race for the neutrino mass hierarchy
The determination of the ordering of the neutrino masses (the hierarchy) is probably a crucial prerequisite to understand the origin of lepton masses and mixings and to establish their relationship to the analogous properties in the quark sector. Here, we follow an alternative strategy to the usual neutrino--antineutrino comparison in long baseline neutrino oscillation experiments: we exploit the combination of the neutrino-only data from the NOvA and the T2K experiments by performing these two off-axis experiments at different distances but at the same $ /L$, where $ $ is the mean neutrino energy and $L$ is the baseline. This would require a minor adjustment to the proposed off-axis angle for one or both of the proposed experiments.
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Resolving theta_{23} Degeneracy by Accelerator and Reactor Neutrino Oscillation Experiments
If the lepton mixing angle theta_{23} is not maximal, there arises a problem of ambiguity in determining theta_{23} due to the existence of two degenerate solutions, one in the first and the other in the second octant. We discuss an experimental strategy for resolving the theta_{23} octant degeneracy by combining reactor measurement of theta_{13} with accelerator nu_{mu} disappearance and nu_{e} appearance experiments. The robustness of the theta_{23} degeneracy and the difficulty in lifting it only by accelerator experiments with conventional nu_{mu} (and nu_{mu}-bar) beam are demonstrated by analytical and numerical treatments. Our method offers a way to overcome the difficulty and can resolve the degeneracy between solutions sin^2 theta_{23} = 0.4 and sin^2 theta_{23} = 0.6 if sin^2 (2 theta_{13}) \gsim 0.05 at 95% CL by assuming the T2K phase II experiment and a reactor measurement with an exposure of 10 GW.kt.yr. The dependence of the resolving power of the octant degeneracy on the systematic errors of reactor experiments is also examined.
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On the Mass Eigenstate Purity of B^8 Solar Neutrinos
We give a brief report on our recent paper, hep-ph/0601198, in which we calculate the nu_2 mass eigenstate purity of B^8 solar neutrinos as 91 +/- 2 %.
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What Fraction of Boron-8 Solar Neutrinos arrive at the Earth as a nu_2 mass eigenstate?
We calculate the fraction of B^8 solar neutrinos that arrive at the Earth as a nu_2 mass eigenstate as a function of the neutrino energy. Weighting this fraction with the B^8 neutrino energy spectrum and the energy dependence of the cross section for the charged current interaction on deuteron with a threshold on the kinetic energy of the recoil electrons of 5.5 MeV, we find that the integrated weighted fraction of nu_2's to be 91 \pm 2 % at the 95% CL. This energy weighting procedure corresponds to the charged current response of the Sudbury Neutrino Observatory (SNO). We have used SNO's current best fit values for the solar mass squared difference and the mixing angle, obtained by combining the data from all solar neutrino experiments and the reactor data from KamLAND. The uncertainty on the nu_2 fraction comes primarily from the uncertainty on the solar delta m^2 rather than from the uncertainty on the solar mixing angle or the Standard Solar Model. Similar results for the Super-Kamiokande experiment are also given. We extend this analysis to three neutrinos and discuss how to extract the modulus of the Maki-Nakagawa-Sakata mixing matrix element U_{e2} as well as place a lower bound on the electron number density in the solar B^8 neutrino production region.
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Establishing neutrino mass hierarchy and CP violation by two identical detectors with different baselines using the J-PARC neutrino beam
We discuss how and to what extent one can determine the neutrino mass hierarchy, normal or inverted, and at the same time uncover CP violation in the lepton sector by using two identical detectors with different baselines in neutrino oscillation experiments using low energy superbeam from the J-PARC facility.
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Resolving Neutrino Mass Hierarchy and CP Degeneracy by Two Identical Detectors with Different Baselines
We explore the possibility of simultaneous determination of neutrino mass hierarchy and the CP violating phase by using two identical detectors placed at different baseline distances. We focus on a possible experimental setup using neutrino beam from J-PARC facility in Japan with beam power of 4MW and megaton (Mton)-class water Cherenkov detectors, one placed in Kamioka and the other at somewhere in Korea. We demonstrate, under reasonable assumptions of systematic uncertainties, that the two-detector complex with each fiducial volume of 0.27 Mton has potential of resolving neutrino mass hierarchy up to sin^2 2theta_{13} > 0.03 (0.055) at 2σ(3σ) CL for any values of delta and at the same time has the sensitivity to CP violation by 4 + 4 years running of nu_e and nu_e-bar appearance measurement. The significantly enhanced sensitivity is due to clean detection of modulation of neutrino energy spectrum, which is enabled by cancellation of systematic uncertainties between two identical detectors which receive the neutrino beam with the same energy spectrum in the absence of oscillations.
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Another possible way to determine the Neutrino Mass Hierarchy
We show that by combining high precision measurements of the atmospheric delta m^2 in both the electron and muon neutrino (or anti-neutrino) disappearance channels one can determine the neutrino mass hierarchy. The required precision is a very challenging fraction of one per cent for both measurements. At even higher precision, sensitivity to the cosine of the CP violating phase is also possible. This method for determining the mass hierarchy of the neutrino sector does not depend on matter effects.
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Long Baseline Neutrino Oscillations: Parameter Degeneracies and JHF/NuMI Complementarity
A summary of the parameter degeneracy issue for long baseline neutrino oscillations is presented and how a sequence of measurements can be used to resolve all degeneracies. Next, a comparison of the JHF and NuMI Off-Axis proposals is made with emphasis on how both experiments running neutrinos can distinguish between the normal and inverted hierarchies provided the E/L of NuMI is less than or equal to the E/L of JHF. Due to the space limitations of this proceedings only an executive style summary can be presented here, but the references and transparencies of the talk contain the detailed arguments.
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CP and T Violation in Neutrino Oscillations
In this short lecture, we discuss some basic phenomenological aspects of CP and T violation in neutrino oscillation. Using CP/T trajectory diagrams in the bi-probability space, we try to sketch out some essential features of the interplay between the effect of CP/T violating phase and that of the matter in neutrino oscillation.
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The Complementarity of Eastern and Western Hemisphere Long-Baseline Neutrino Oscillation Experiments
We present a general formalism for extracting information on the fundamental parameters associated with neutrino masses and mixings from two or more long baseline neutrino oscillation experiments. This formalism is then applied to the current most likely experiments using neutrino beams from the Japan Hadron Facility (JHF) and Fermilab's NuMI beamline. Different combinations of muon neutrino or muon anti-neutrino running are considered. To extract the type of neutrino mass hierarchy we make use of the matter effect. Contrary to naive expectation, we find that both beams using neutrinos is more suitable for determining the hierarchy provided that the neutrino energy divided by baseline ($E/L$) for NuMI is smaller than or equal to that of JHF. Whereas to determine the small mixing angle, $θ_{13}$, and the CP or T violating phase $δ$, one neutrino and the other anti-neutrino is most suitable. We make extensive use of bi-probability diagrams for both understanding and extracting the physics involved in such comparisons.
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Parameter Degeneracies in Neutrino Oscillation Measurement of Leptonic CP and T Violation
The measurement of the mixing angle θ_{13}, sign of Δm^2_{13} and the CP or T violating phase δis fraught with ambiguities in neutrino oscillation. In this paper we give an analytic treatment of the paramater degeneracies associated with measuring the ν_μ-> ν_e probability and its CP and/or T conjugates. For CP violation, we give explicit solutions to allow us to obtain the regions where there exist two-fold and four-fold degeneracies. We calculate the fractional differences, Δθ/ \barθ, between the allowed solutions which may be used to compare with the expected sensitivities of the experiments. For T violation we show that there is always a complete degeneracy between solutions with positive and negative Δm^2_{13} which arises due to a symmetry and cannot be removed by observing one neutrino oscillation probability and its T conjugate. Thus, there is always a four fold parameter degeneracy apart from exceptional points. Explicit solutions are also given and the fractional differences are computed. The bi-probability CP/T trajectory diagrams are extensively used to illuminate the nature of the degeneracies.
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