Sin2 2θ13 Research Articles

Constraints on neutrino decay lifetime using long-baseline charged and neutral current data

We investigate the status of a scenario involving oscillations and decay for charged and neutral current data from the MINOS and T2K experiments. We first present an analysis of charged current neutrino and anti-neutrino data from MINOS in the framework of oscillation with decay and obtain a best fit for non-zero decay parameter α3. The MINOS charged and neutral current data analysis results in the best fit for |Δm322|=2.34×10−3 eV2, sin2⁡θ23=0.60 and zero decay parameter, which corresponds to the limit for standard oscillations. Our combined MINOS and T2K analysis reports a constraint at the 90% confidence level for the neutrino decay lifetime τ3/m3>2.8×10−12 s/eV. This is the best limit based only on accelerator produced neutrinos.

A partial μ–τ symmetry and its prediction for leptonic CP violation

We find that the lepton flavor mixing matrix U should possess a partial μ–τ permutation symmetry |Uμ1|=|Uτ1|, and the latter predicts a novel correlation between the Dirac CP-violating phase δ and three flavor mixing angles θ12, θ13 and θ23 in the standard parametrization. Inputting the best-fit values of these angles reported by Capozzi et al., we obtain the prediction δ≃255° in the normal neutrino mass ordering, which is in good agreement with the best-fit result δ≃250°. In this connection the inverted neutrino mass ordering is slightly disfavored. If this partial μ–τ symmetry is specified to be |Uμ1|=|Uτ1|=1/6, one can reproduce the phenomenologically-favored relation sin2⁡θ12=(1−2tan2⁡θ13)/3 and a viable two-parameter description of U which were first uncovered in 2006. Moreover, we point out that the octant of θ23 and the quadrant of δ can be resolved due to the slight violation of |Uμ2|=|Uτ2| and |Uμ3|=|Uτ3| either at the tree level or from radiative corrections.

The Daya Bay and T2K results on [formula omitted] and non-standard neutrino interactions

We show that the relatively large best fit value of sin2⁡2θ13=0.14(0.17) measured in the T2K experiment for fixed values of i) the Dirac CP violation phase δ=0, and ii) the atmospheric neutrino mixing parameters θ23=π/4, |Δm322|=2.4×10−3 eV2, can be reconciled with the Daya Bay result sin2⁡2θ13=0.090±0.009 if the effects of non-standard neutrino interactions (NSI) in the relevant ν¯e→ν¯e and νμ→νe oscillation probabilities are taken into account.

Background-independent measurement of [formula omitted] in Double Chooz

The oscillation results published by the Double Chooz Collaboration in 2011 and 2012 rely on background models substantiated by reactor-on data. In this analysis, we present a background-model-independent measurement of the mixing angle θ13 by including 7.53 days of reactor-off data. A global fit of the observed antineutrino rates for different reactor power conditions is performed, yielding a measurement of both θ13 and the total background rate. The results on the mixing angle are improved significantly by including the reactor-off data in the fit, as it provides a direct measurement of the total background rate. This reactor rate modulation analysis considers antineutrino candidates with neutron captures on both Gd and H, whose combination yields sin2(2θ13)=0.102±0.028(stat.)±0.033(syst.). The results presented in this study are fully consistent with the ones already published by Double Chooz, achieving a competitive precision. They provide, for the first time, a determination of θ13 that does not depend on a background model.

Precise measurement of the neutrino mixing parameter θ23 from muon neutrino disappearance in an off-axis beam.

New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter θ23. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57×10(20) protons on target, T2K has fit the energy-dependent νμ oscillation probability to determine oscillation parameters. The 68% confidence limit on sin(2)(θ23) is 0.514(-0.056)(+0.055) (0.511±0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Δm32(2)=(2.51±0.10)×10(-3) eV(2)/c(4) (inverted hierarchy: Δm13(2)=(2.48±0.10)×10(-3) eV(2)/c(4)). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.

Results on θ13Neutrino Oscillations from Reactor Experiments

Definitive measurements of the smallest neutrino mixing angle θ13 were made by Daya Bay, Double Chooz and RENO in 2012, based on the disappearance of electron antineutrinos emitted from reactors. The new generation reactor experiments have significantly improved a sensitivity for θ13 down to the sin2(2θ13)~0.01 level using two identical detectors of 10 ~ 40 tons at near (300 ~ 400 m) and far (1 ~ 2 km) locations. The θ13 measurements by the three reactor experiments are presented with their future expected sensitivities.

Low Energy Investigations at Kamioka Observatory

At Kamioka Observatory many activities for low energy rare event search are ongoing. Super-Kamiokande(SK), the largest water Cherenkov neutrino detector, currently continues data taking as the fourth phase of the experiment (SK-IV). In SK-IV, we have upgraded the water purification system and tuned water flow in the SK tank. Consequently the background level was lowered significantly. This allowed SK-IV to derive solar neutrino results down to 3.5 MeV energy region. With these data, neutrino oscillation parameters are updated from global fit; Δm212 = 7.44+0.2−0.19 × 10−5eV2, sin2 θ12 = 0.304 ± 0.013, sin2 θ13 = 0.0301+0.017−0.015. NEWAGE, the directional sensitive dark matter search experiment, is currently operated as "NEWAGE-0.3a" which is a 0.20 × 0.25 × 0.31 m3 micro-TPC filled with CF4 gas at 152 Torr. Recently we have developed "NEWAGE-0.3b". It was succeeded to lower the operation pressure down to 76 Torr and the threshold down to 50 keV (F recoils). XMASS experiment is looking for scintillation signals from dark matter interaction in 1 ton of liquid xenon. It was designed utilizing its self-shielding capability with fiducial volume confinement. However, we could lower the analysis threshold down to 0.3 keVee using whole volume of the detector. In February 2012, low threshold and very large exposure data (5591 kg·days) were collected. With these data, we have excluded some part of the parameter spaces claimed by DAMA/LIBRA and CoGeNT experiments.

Evidence of electron neutrino appearance in a muon neutrino beam

The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, |Δm322|≈2.4×10−3 eV2. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam’s origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3±0.4(syst) events is expected. The background-only hypothesis is rejected with a p value of 0.0009 (3.1σ), and a fit assuming νμ→νe oscillations with sin22θ23=1, δCP=0 and |Δm322|=2.4×10−3 eV2 yields sin22θ13=0.088−0.039+0.049(stat+syst).35 MoreReceived 4 April 2013DOI:https://doi.org/10.1103/PhysRevD.88.032002© 2013 American Physical Society

Reactor on-off antineutrino measurement with KamLAND

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ν¯e flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ν¯e oscillation analysis. The data set also has improved sensitivity for other ν¯e signals, in particular ν¯e’s produced in β-decays from U238 and Th232 within the Earth’s interior, whose energy spectrum overlaps with that of reactor ν¯e’s. Including constraints on θ13 from accelerator and short-baseline reactor neutrino experiments, a combined three-flavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of tan2θ12=0.436−0.025+0.029, Δm212=7.53−0.18+0.18×10−5 eV2, and sin2θ13=0.023−0.002+0.002. Assuming a chondritic Th/U mass ratio, we obtain 116−27+28 ν¯e events from U238 and Th232, corresponding to a geo ν¯e flux of 3.4−0.8+0.8×106 cm−2 s−1 at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo ν¯e rate.1 MoreReceived 19 March 2013DOI:https://doi.org/10.1103/PhysRevD.88.033001© 2013 American Physical Society

Experimental search for the LSND anomaly with the ICARUS LAr-TPC detector in the CNGS beam

We report an early result from ICARUS (CNGS2), the large mass LAr-TPC, a Gargamelle class imaging detector of novel design. A search of a vμ → νe signal due to a LSND anomaly at the Gran Sasso Laboratory, located at a distance of L = 730 km from CERN is hereby presented. Such an anomaly, in which an electron is produced by neutrinos in the energy interval 0 ≤ Ev ≤ 30 GeV, will be characterized by a fast energy oscillation averaging closely to sin2(1.27Δm2newL/Ev) ≃ 1/2 and therefore approximately with probability . The presence of such a signal will be compared with the small but significant backgrounds due to other and more conventional neutrino origins. Within the range of our observations, our result is compatible with the absence of a LSND anomaly. At 90% and 99% confidence levels the limits on the oscillation probabilities are and respectively. The present result strongly limits the window of opened options for the LSND anomaly, reducing the remaining effect to a narrow region centered around (Δm2, sin2(2θ)) = (0.5 eV2,0.05) where there is an over-all agreement (at 90 % CL) between the present ICARUS limit, the published limits of KARMEN and the published positive signals of LSND and MiniBooNE collaborations.

Measurement of Neutrino and Antineutrino Oscillations Using Beam and Atmospheric Data in MINOS

We report measurements of oscillation parameters from ν(μ) and ν(μ) disappearance using beam and atmospheric data from MINOS. The data comprise exposures of 10.71×10(20) protons on target in the ν(μ)-dominated beam, 3.36×10(20) protons on target in the ν(μ)-enhanced beam, and 37.88 kton yr of atmospheric neutrinos. Assuming identical ν and ν oscillation parameters, we measure |Δm2| = (2.41(-0.10)(+0.09))×10(-3) eV2 and sin2(2θ) = 0.950(-0.036)(+0.035). Allowing independent ν and ν oscillations, we measure antineutrino parameters of |Δm2| = (2.50(-0.25)(+0.23))×10(-3) eV2 and sin2(2θ) = 0.97(-0.08)(+0.03), with minimal change to the neutrino parameters.

θ13 and the Higgs Mass from High Scale Supersymmetry

In the framework in which supersymmetry is used for understanding fermion masses rather than stabilizing the electroweak scale, we elaborate on the phenomenological analysis for the neutrino physics. A relatively large sin θ13 ≃ 0.13 is naturally obtained. The model further predicts vanishingly small CP violation in neutrino oscillations. While the high scale supersymmetry generically results in a Higgs mass of about 141 GeV, our model reduces this mass to 126 GeV via introducing SU(2)L triplet fields which make the electroweak vacuum metastable (with a safe lifetime) and also contribute to neutrino masses.

Double Chooz: Results and Perspectives

The Double Chooz experiment has been observing ν¯e from two reactor cores at the Chooz nuclear power station in Ardennes, France, with a single 10.3 m3 fiducial volume Gd-doped liquid scintillator detector at a flux-weighted average baseline of ∼1050 m. This article reviews results achieved with a detector live time of 227.93 days and exposure of 33.71 GW-ton-years. A total of 8,249 candidate ν¯e events have been observed, compared to an expected 8,937 events in the null-oscillation case: this deficit is interpreted as evidence for ν¯e disappearance. A fit to the observed neutrino rate and spectral shape gives a best-fit value of sin2(2θ13)=0.109±0.030(stat.)±0.025(syst.) at a mass-squared splitting of Δm312=2.32×10−3 eV2. The null-oscillation hypothesis is excluded by the data at 99.8% CL (2.9σ). The Double Chooz Near Detector is under construction, and analysis efforts to measure neutrino directionality, test Lorentz violation, and measure backgrounds in situ are underway.

T2K Results and Perspectives

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a 600 MeV off-axis, high intensity muon-neutrino beam sent 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are the search for the appearance of electron neutrinos at SK resulting from θ13>0 and a precise measurement of θ23 and Δm322 via the νμ disappearance channel. The T2K collaboration has already published indications of electron neutrino appearance [K. Abe et al., Phys. Rev. Lett. 107, 041801 (2011)] and a first measurement of sin2(θ23) from muon neutrino disappearance [K. Abe et al., Phys. Rev. D 85,(2011) 031103] using the data collected until March 11, 2011. An improved analysis and all the data taken through June 9, 2012 provide now 11 electron neutrino candidates in the far detector, corresponding to 3.2 standard deviations from the θ13=0 hypothesis. This excess is currently the strongest evidence of electron neutrino appearance and it yields, for normal hierarchy and δCP=0,0.053<sin22θ13<0.141 at 68% confidence level.

Mass hierarchy determination using current and upcoming neutrino experiments

Determination of mass hierarchy is a crucial open ended question in neutrino physics today. In the wake of recent T2K [1], MINOS [2] and DChooz [3] results which support a high best-fit to θ13, it is worthwhile to explore the potential of the upcoming and already running neutrino experiments for determining mass hierarchy. We consider the long baseline experiments NOνA and T2K and the reactor neutrino experiments Daya Bay, DChooz and RENO. In our analysis we find out that NOνA by itself is insufficient and would require another long baseline experiment such as T2K. This work assumes that by the time reactor neutrino experiments are over, we will have a precise θ13 information. Final results are presented as hierarchy exclusion plots in sin2 2θ13 − δCP plane.

Implications of nonzero θ13 for the neutrino mass hierarchy

The Daya Bay, RENO, and Double Chooz experiments have discovered a large non-zero value for θ13. We present a global analysis that includes these three experiments, Chooz, the Super-K atmospheric data, and the νμ → νe T2K and MINOS experiments that are sensitive to the hierarchy and the sign of θ13. We report preliminary results in which we fix the mixing parameters other than θ13 to those from a recent global analysis. Given there is no evidence for a non-zero CP violation, we assume δ = 0. T2K and MINOS lie in a region of L/E where there is a hierarchy degeneracy in the limit of θ13 → 0 and no matter interaction. For nonzero θ13, the symmetry is partially broken, but a degeneracy under the simultaneous exchange of both hierarchy and the sign of θ13 remains. Matter effects break this symmetry such that the positions of the peaks in the oscillation probabilities maintain the two-fold symmetry, while the magnitude of the oscillations is sensitive to the hierarchy. This renders T2K and NOvA, with different baselines and different matter effects, better able in combination to distinguish the hierarchy and the sign of θ13. The present T2K and MINOS data do not distinguish between hierarchies or the sign of θ13, but the large value of θ13 yields effects from atmospheric data that do. We find for normal hierarchy, positive θ13, sin2 2θ13 = 0.090 ± 0.020 and is 0.2% probable it is the correct combination; for normal hierarchy, negative θ13, sin2 2θ13 = 0.108 ± 0.023 and is 2.2% probable; for inverse hierarchy, positive θ13, sin2 2θ13 = 0.110±0.022 and is 7.1% probable; for inverse hierarchy, negative θ13, sin2 2θ13 = 0.113 ± 0.022 and is 90.5% probable, results that are inconsistent with two similar analyses.

The Double Chooz Experiment

The Double Chooz neutrino oscillations experiment is expected to measure, or limit, the unmeasured leptonic mixing angle θ13 using neutrinos from the Chooz reactor complex (France). The experimental technique relies on two detectors to reduce the so far dominating neutrino flux uncertainty as well as backgrounds. The DC sensitivity (at 90%CL) is sin2(2θ13)<0.054 and sin2(2θ13)<0.030, for the far detector only (1.5 years) and near/far detectors (3 years), respectively. The far detector is to be filled and completed by the end 2010, while data taking has started since June 2010 (without scintillator).

Implication of MINOS results to neutrino masses

We analyzed the results of Main Injector Neutrino Oscillation Search (MINOS) that constrain the neutrino mixing angles θ13 and θ23 in combination. According to the exclusion curve obtained from recent experimental results, the mass spectrum of the normal hierarchy is disfavored. A model is constructed and examined to explain the compatibility of the model and the phenomenologically allowed parameter region in sin θ23vs. sin θ13. The prediction of the model, which contains certain criteria in the ratio of non-Standard Model additional Higgs scales, results in an inverted hierarchy in masses, 1 < m2/m3 < 1.7.

The Daya Bay Muon Veto System

The goal of the Daya Bay reactor neutrino experiment is to measure θ13 with a sensitivity in sin2(2θ13) of 0.01. To achieve this, the cosmic ray induced backgrounds must be reduced to a low level. Daya Bayʼs muon veto system will consist of a 2.5 m active water shield and RPCs. The muon tagging efficiency of the combined system is expected to be at least 99.5%. The details of the muon system and estimates of the expected backgrounds will be described.

A Mineral Oil Monitoring System for the Daya Bay Neutrino Experiment

The Daya Bay Reactor Neutrino Experiment expects to determine the neutrino mixing angle θ13 with a sensitivity of sin2(2θ13)=0.01 in a three-year run. Eight three-zone cylindrical Anti-neutrino Detector (AD) modules with Gd-doped Liquid Scintillator are arranged in two near halls and a far hall. In the outermost zone of each AD, 192 PMTs are mounted in Mineral Oil (MO). The stability of the optical properties of the liquids is very important for controlling the systematic uncertainties of the experiment and thus will be monitored online. The design of a monitoring system for the MO and results from a prototype system is presented.