Resolving the eightfold neutrino parameter degeneracy by two identical detectors with different baselines

Department of Physics, Tokyo Metropolitan University, Edo, Tōkyō, Japan
Physical review D: Particles and fields (Impact Factor: 4.86). 01/2007; 75(1). DOI: 10.1103/PhysRevD.75.013006
Source: arXiv


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 θ23 octant degeneracy in region where sin⁡22θ23≲0.97 at 2 standard deviation confidence level even for very small values of θ13. Altogether, it is demonstrated that one can solve all the eightfold neutrino parameter degeneracies in situ by using the Tokai-to-Kamioka-Korea setting if θ13 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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    • "Adding the information from the 'silver' channel (ν e → ν τ ) to the 'golden' channel (ν e → ν µ ) in the proposed neutrino factory setup is demonstrated to be one of the elegant ways to tackle this degeneracy [46] [47]. The possibility of determining the deviation of θ 23 from maximal mixing and consequently the correct octant of θ 23 in very long-baseline neutrino oscillation experiments and as well as in future atmospheric neutrino experiments has been discussed in [48] [49] [50] [51] [52] [53] [54] [55] [56]. One clear message that has been conveyed by all these novel works is that one can achieve a very good sensitivity to the quantity |0.5 − sin 2 θ 23 | from the conventional beam experiments (MINOS, ICARUS and OPERA), the current generation superbeam experiments (presently running T2K and upcoming NOνA), and also from the current (Super-Kamiokande) and future atmospheric data (India-based Neutrino Observatory). "
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    ABSTRACT: Preliminary results of MINOS experiment indicate that theta23 is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for theta23: one in the lower octant (LO: theta23 < 45 degree) and the other in the higher octant (HO: theta23 > 45 degree). numu to nue oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOvA experiments. Because of the hierarchy-deltacp degeneracy and the octant-deltacp degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of deltacp for which octant resolution is easy (challenging). However, for octant resolution the unfavorable deltacp values of the neutrino data are favorable for the anti-neutrino data and vice-verse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NOvA to resolve the octant ambiguity. If sin^2\theta23 =0.41, then NOvA can rule out all the values of theta23 in HO at 2 sigma C.L., irrespective of the hierarchy and deltacp. Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and anti-neutrino runs of 2.5 years each, a 2 sigma resolution of the octant becomes possible provided sin^2\theta23 \leq 0.43 or \geq 0.58 for any value of deltacp.
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    ABSTRACT: The Cervera et al. formula, the best known approximate formula of neutrino oscillation probability for long-baseline experiments, can be regarded as a second-order perturbative formula with small expansion parameter ϵ ≡ ∆m 212 ∆m 312 ≃ 0.03 under the 21assumption s 13 ≃ ϵ. If θ 13 is large, as suggested by a candidate ν e event at T2K as well as the recent global analyses, higher order corrections of s 13 to the formula would be needed for better accuracy. We compute the corrections systematically by formulating a perturbative framework by taking θ 13 as s13 ~ Ö{ Î } @ 0.18 {s_{13}} \sim \sqrt { \in } \simeq 0.18 , which guarantees its validity in a wide range of θ 13 below the Chooz limit. We show on general ground that the correction terms must be of order ϵ2. Yet, they nicely fill the mismatch between the approximate and the exact formulas at low energies and relatively long baselines. General theorems are derived which serve for better understanding of δ-dependence of the oscillation probability. Some interesting implications of the large θ 13 hypothesis are discussed. KeywordsNeutrino Physics–Beyond Standard Model–Standard Model
    Journal of High Energy Physics 03/2011; 2011(6):1-26. DOI:10.1007/JHEP06(2011)022 · 6.11 Impact Factor
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