Neutrinos; Opportunities and Strategies in the Future (original) (raw)
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Phenomenology of future neutrino experiments with large
Nuclear Physics B - Proceedings Supplements, 2013
The question "how small is the lepton mixing angle θ13?" had a convincing answer in a surprisingly short time, θ13 ≃ 9 • , a large value comparable to the Chooz limit. It defines a new epoch in the program of determining the lepton mixing parameters, opening the door to search for lepton CP violation of the Kobayashi-Maskawa-type. I discuss influences of the large value of θ13 to search for CP violation and determination of the neutrino mass hierarchy, the remaining unknowns in the standard three-flavor mixing scheme of neutrinos. I emphasize the following two points: (1) Large θ13 makes determination of the mass hierarchy easier. It stimulates to invent new ideas and necessitates quantitative reexamination of practical ways to explore it. (2) However, large θ13 does not quite make CP measurement easier so that we do need a "guaranteeing machine" to measure CP phase δ.
Journal of High Energy Physics, 2008
If the atmospheric neutrino oscillation amplitude, sin 2 2θ ATM is not maximal, there is a two fold ambiguity in the neutrino parameter space: sin 2 θ ATM > 0.5 or sin 2 θ ATM < 0.5. In this article, we study the impact of this degeneracy, the so-called octant degeneracy, on the T2KK experiment, which is a proposed extension of the T2K (Tokai-to-Kaimoka) neutrino oscillation experiment with an additional waterČerenkov detector placed in Korea. We find that the degeneracy between sin 2 θ ATM = 0.40 and 0.60 can be resolved at the 3σ level for sin 2 2θ RCT > 0.12 (0.08) for the optimal combination of a 3.0 • off-axis beam (OAB) at SK (L = 295km) and a 0.5 • OAB at L = 1000km with a far detector of 100kton volume, after 5 years of exposure with 1.0 (5.0) × 10 21 POT/year, if the hierarchy is normal. We also study the influence of the octant degeneracy on the capability of T2KK experiment to determine the mass hierarchy and the leptonic CP phase. The capability of rejecting the wrong mass hierarchy grows with increasing sin 2 θ ATM when the hierarchy is normal, whereas it is rather insensitive to sin 2 θ ATM for the inverted hierarchy. We also find that the 1σ allowed region of the CP phase is not affected significantly even when the octant degeneracy is not resolved. All our results are obtained for the 22.5 kton Super-Kamiokande as a near detector and without an anti-neutrino beam.
Toward exploring unknowns in the lepton flavor mixing
Nuclear Physics B - Proceedings Supplements, 2004
In this talk I focus in on some of the relatively unexplored aspects of neutrino masses and lepton flavor mixing. They are (1) possible deviation of θ 23 from the maximal, and (2) serious consequences of our ignorance of the sign of ∆m 2 13 on the interpretation of future CP violation measurement. I emphasize that the accuracy of s 2 23 determination that already achieved by the Super-Kamiokande atmospheric neutrino observation will not be improved significantly by the next-generation LBL experiments for nearly maximal θ 23. I also stress that, unless we know the sign of ∆m 2 13 , detection of CP violation in the JPARC-SK experiment would suffer from the problem of confusion to CP conservation. Clearly, better strategies which so far escaped our attention are called for to determine these quantities.
Exploring Leptonic CP Violation by Reactor and neutrino Superbeam Experiments
Nuclear Physics B - Proceedings Supplements, 2005
We point out the possibility that reactor measurement of θ 13 , when combined with high-statistics ν e appearance accelerator experiments, can detect leptonic CP violation. Our proposal is based on a careful statistical analysis under reasonable assumptions on systematic errors, assuming 2 years running of the neutrino mode J-PARC → Hyper-Kamiokande experiment and a few years running of a reactor experiment with 100ton detectors at the Kashiwazaki-Kariwa nuclear power plant. We show that the method can be arranged to be insensitive to the intrinsic parameter degeneracy but is affected by the one due to unknown sign of ∆m 2 31 .
Through Neutrino Eyes: The Search for New Physics
Advances in High Energy Physics, 2015
The year 2014 will mark the 60th anniversary since the neutrino detector of Frederick Reines and Clyde L. Cowan, Jr. was turned (neutrino detection in 1956). After many years, Super-Kamiokande showed in 1998 that neutrinos are massive. Today, neutrino physics has become a very active research field: there is a plethora of different neutrino experiments and theoretical studies. Subsequent measurements [2-6] of the two neutrino mass squared differences and the leptonic mixing parameters lead to a phase of precision experiments in neutrino physics. Recently the last remaining mixing angle, the 1-3 mixing angle, has been measured by the Daya Bay , Double Chooz [9, 10], and RENO [11] experiments after initial hints by T2K [12] and MINOS . Contrary to theoretical expectations from flavor symmetry considerations, it turned out to be large.
Neutrinos: summarizing the state-of-the-art
2002
I review oscillation solutions to the neutrino anomalies and discuss how to account for the required pattern of neutrino masses and mixings from first principles. Unification and low-energy bottom-up approaches are discussed, the latter open up the possibility of testing neutrino mixing at high energy colliders, such as the LHC. Large νe mixing is consistent with Supernova (SN) astrophysics and may serve to probe galactic SN parameters at Cherenkov detectors. I discuss the robustness of the atmospheric neutrino oscillation hypothesis against the presence of Flavor Changing (FC) Non-Standard neutrino Interactions (NSI), generally expected in models of neutrino mass. Atmospheric data strongly constrain FC-NSI in the νµ -ντ channel, while solar data can be explained by FC-NSI in the νe -ντ channel, or, alternatively, by spin flavor precession. I illustrate how a neutrino factory offers a unique way to probe for FC-NSI and argue that a near-site detector is necessary in order to probe for leptonic mixing and CP violation.
Looking for Leptonic CP Violation with Neutrinos
Acta Physica Polonica Series B, 2008
I discuss some theoretical aspects of how to observe leptonic CP violation. It is divided into two parts, one for CP violation due to Majorana, and the other more conventional leptonic Kobayashi-Maskawa (KM) phases. In the first part, I estimate the effect of Majorana phase to observable of neutrinoless double beta decay experiments by paying a careful attention to the definition of the atmospheric scale ∆m 2. In the second part, I discuss Tokai-to-Kamioka-Korea two detector complex which receives neutrino superbeam from J-PARC as a concrete setting for discovering CP violation due to the KM phase, as well as resolving mass hierarchy and the θ 23 octant degeneracy. A cautionary remark is also given on comparison between various projects aiming at exploring CP violation and the mass hierarchy.
Phenomenology of future long-baseline neutrino experiments
Journal of Physics: Conference Series, 2008
I review some basic ideas behind possible future long-baseline neutrino experiments to determine the neutrino mass hierarchy and uncover leptonic CP violation. With emphasis of "large θ13" hypothesis I try to illuminate the principles of the conventional method for resolving the mass hierarchy by using the earth matter effect, and for detecting CP violation as a vacuum effect. They include the VLBL on-axis approach and the two-detector method. Some unconventional ideas for reaching the same goal are also mentioned.
Physical Review D, 2007
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 < ∼ 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.