arXiv subjects

O. Yasuda

Publications and source records attributed to O. Yasuda.

11 recordsLinked to original sources

arXiv2007

CP-violation from non-unitary leptonic mixing

A low-energy non-unitary leptonic mixing matrix is a generic effect of a large class of theories accounting for neutrino masses. It is shown how the extra CP-odd phases of a general non-unitary matrix allow for sizeable CP-asymmetries in channels other than those dominant in the standard unitary case. The $ν_μ\to ν_τ$ channel turns out to be an excellent tool to further constrain moduli and phases. Furthermore, we clarify the relationship between our approach and the so-called "non-standard neutrino interactions" schemes: the sensitivities explored here apply as well to such constructions.

hep-ph↗

arXiv2006

Letter of Intent for KASKA: High Accuracy Neutrino Oscillation Measurements with anti-nu_es from Kashiwazaki-Kariwa Nuclear Power Station

One of the current most-demanded experiments in neutrino physics is to measure the last mixing angle theta_13. KASKA is an experiment to detect new type of reactor neutrino oscillation and to measure sin^2 2theta_13 accurately using the world's most powerful nuclear reactor complex; Kashiwazaki-Kariwa nuclear power station. KASKA utilizes near and far detectors of identical structure at nearly optimized baselines and underground depths to cancel most of the systematics and reduce backgrounds. The expected sensitivity is sin^2 2theta_13~0.015, which is 10 times better sensitivity than the current upper limit measured by CHOOZ reactor experiment. Extension of KASKA project has potential to accurately measure other anti-nu_e oscillation parameters. Intense and precisely known neutrino flux measured by the KASKA-theta_13 phase can be used to pin down sin^2 2theta_12 at a baseline ~50km and to measure Dm^2_13 for the first time at a baseline ~5km. This Letter of Intent describes physics motivation, detector system and expected performance of the KASKA experiment.

hep-ex↗

arXiv2005

A formula for the sensitivity to sin^2{2theta_13} in reactor experiments with a spectral analysis

Using an analytical approach, the sensitivity to sin^2{2theta_13} with infinite statistics in a spectral analysis is investigated in reactor neutrino oscillation experiments with one reactor and two identical detectors. We derive an useful formula for the sensitivity which depends only two parameters sigma_db/\sqrt{n} (the uncorrelated bin-to-bin systematic error over the square-root of the number of bins) and sigma_dB (the bin-to-bin correlated detector specific systematic error).

hep-ph↗

arXiv2004

Systematic limits on sin^2{2theta_{13}} in neutrino oscillation experiments with multi-reactors

Sensitivities to sin^2{2theta_{13}} without statistical errors (``systematic limit'') are investigated in neutrino oscillation experiments with multiple reactors. Using an analytical approach, we show that the systematic limit on sin^2{2theta_{13}} is dominated by the uncorrelated systematic error sigma_u of the detector. Even in an experiment with multi-detectors and multi-reactors, it turns out that most of the systematic errors including the one due to the nature of multiple sources is canceled as in the case with a single reactor plus two detectors, if the near detectors are placed suitably. The case of the KASKA plan (7 reactors and 3 detectors) is investigated in detail, and it is explicitly shown that it does not suffer from the extra uncertainty due to multiple reactors.

hep-ph↗

arXiv2003

Reactor Measurement of $θ_{13}$ and Its Complementarity to Long-Baseline Experiments

A possibility to measure $\sin^22θ_{13}$ using reactor neutrinos is examined in detail. It is shown that the sensitivity $\sin^22θ_{13}>0.02$ can be reached with 20 ton-year data by placing identical CHOOZ-like detectors at near and far distances from a giant nuclear power plant whose total thermal energy is 24.3 ${\text{GW}_{\text{th}}}$. It is emphasized that this measurement is free from the parameter degeneracies which occur in accelerator appearance experiments, and therefore the reactor measurement plays a role complementary to accelerator experiments. It is also shown that the reactor measurement may be able to resolve the degeneracy in $θ_{23}$ if $\sin^22θ_{13}$ and $\cos^22θ_{23}$ are relatively large.

hep-ph↗

arXiv2000

Effects of neutrino mixing on high-energy cosmic neutrino flux

Several cosmologically distant astrophysical sources may produce high-energy cosmic neutrinos (E \geq 10^6 GeV) of all flavors above the atmospheric neutrino background. We study the effects of vacuum neutrino mixing in three flavor framework on this cosmic neutrino flux. We also consider the effects of possible mixing between the three active neutrinos and the (fourth) sterile neutrino with or without Big-Bang nucleosynthesis constraints and estimate the resulting final high-energy cosmic neutrino flux ratios on earth compatible with currently existing different neutrino oscillation hints in a model independent way. Further, we discuss the case where the intrinsic cosmic neutrino flux does not have the standard ratio.

hep-ph↗

arXiv1998

Atmospheric Neutrino Tests of Neutrino Oscillation Mechanisms

Recent Super-Kamiokande data on the atmospheric neutrino anomaly are used to test various mechanisms for neutrino oscillations. It is found that the current atmospheric neutrino data alone cannot rule out any particular mechanism. Future long-baseline experiments should play an important role in identifying the underlying neutrino oscillation mechanism.

hep-ph↗

arXiv1998

Confronting solutions to the atmospheric neutrino anomaly involving large angle $ν_μ \to ν_e$ oscillations with SuperKamiokande and CHOOZ

Neutrino oscillation scenarios involving large angle $ν_μ \to ν_e$ oscillations are disfavoured in the parameter range $Δm^2/eV^2 >~ 10^{-3}$ by recent results from the CHOOZ reactor-based $\barν_e$ disappearance experiment. For this reason we extend our previous work on up-down asymmetries for various oscillation scenarios by computing up-down asymmetries and the R ratio for the entire conceivable range $10^{-4} - 10^{-1} eV^2$ of $Δm^2$. Matter effects in the Earth play a crucial role. We perform a $χ^2$ fit to the data. We find that, because of the matter effect, the three-flavour maximal mixing model provides a reasonable fit to SuperKamiokande and CHOOZ data provided that the relevant $Δm^2$ is in the range $4 \times 10^{-4} ~< Δm^2/eV^2 ~< 1.5 \times 10^{-3}$.

hep-ph↗

arXiv1998

Comparing and contrasting the $ν_μ \to ν_τ$ and $ν_μ \to ν_s$ solutions to the atmospheric neutrino problem with SuperKamiokande data

The $ν_μ \to ν_τ$ and $ν_μ \to ν_s$ solutions to the atmospheric neutrino problem are compared with SuperKamiokande data. The differences between these solutions due to matter effects in the Earth are calculated for the ratio of $μ$-like to $e$-like events and for up-down flux asymmetries. These quantities are chosen because they are relatively insensitive to theoretical uncertainties in the overall neutrino flux normalisation and detection cross-sections and efficiencies. A $χ^2$ analysis using these quantities is performed yielding $3σ$ ranges which are approximately given by $(0.725 - 1.0, 4 \times 10^{-4} - 2 \times 10^{-2} eV^2)$ and $(0.74 - 1.0, 1 \times 10^{-3} - 2 \times 10^{-2} eV^2)$ for $(\sin^2 2θ,Δm^2)$ for the $ν_μ \to ν_τ$ and $ν_μ \to ν_s$ solutions, respectively. Values of $Δm^2$ smaller than about $2 \times 10^{-3}$ eV$^2$ are disfavoured for the $ν_μ \to ν_s$ solution, suggesting that future long baseline experiments should see a positive signal if this scenario is the correct one.

hep-ph↗

arXiv1997

Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data

Motivated by the Exact Parity Model and other theories, the hypothesis that each of the known neutrinos oscillates maximally with a sterile partner has been put forward as an explanation of the atmospheric and solar neutrino anomalies. We provide detailed predictions for muon and electron flux ratios induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric neutrinos. Several different, carefully chosen cuts on momentum and zenith angle are proposed, emphasizing the role of up-down flux asymmetries.

hep-ph↗

arXiv1997

Up-down atmospheric neutrino flux asymmetry predictions for various neutrino oscillation scenarios

We compute up-down asymmetries for atmospheric neutrino induced electron and muon events in the SuperKamiokande detector for the following neutrino oscillation models: (A) maximally mixed $ν_μ - ν_τ$ or $ν_μ - ν_s$, (B) maximally mixed $ν_μ - ν_e$, (C) threefold maximal mixing between $ν_e, ν_μ$ and $ν_τ$, and (D) neutrino oscillations via Equivalence Principle or Lorentz invariance violation. We emphasise the role of different momentum cuts.

hep-ph↗