RENO Experiments Research Articles

Simplest neutrino mixing from S 4 symmetry

In 2004, two us proposed a texture, the “Simplest” neutrino mass matrix, which predicted $ \sin {\theta_{13 }}=\sqrt{{{{{2\varDelta m_{{^{sol}}}^2}} \left/ {{3\varDelta m_{{^{atm}}}^2}} \right.}}} $ and δ CP = 90°. Using today’s measured values for neutrino mass-squared differences, this prediction gives $ {\sin^2}2{\theta_{13 }}\simeq 0.086_{-0.006}^{+0.003 } $ , compared with a measured value, found by averaging the results of the Daya Bay and RENO experiments, of sin22θ 13 = 0.093 ± 0.010. Here we present a specific model based on S 4 symmetry leading to this successful texture in the context of the type-1 see-saw mechanism, assuming Majorana neutrinos. In this case, slightly different predictions are obtained relating θ 13 to the light neutrino masses, which are in accord with current experimental limits and testable at future experiments. Large CP asymmetries remain a generic prediction of the texture.

Determining the neutrino mass hierarchy with INO, T2K, NOvA and reactor experiments

The relatively large measured value of $\theta_{13}$ has opened up the possibility of determining the neutrino mass hierarchy through earth matter effects. Amongst the current accelerator-based experiments only NOvA has a long enough baseline to observe earth matter effects. However, NOvA is plagued with uncertainty on the knowledge of the true value of $\delta_{CP}$, and this could drastically reduce its sensitivity to the neutrino mass hierarchy. The earth matter effect on atmospheric neutrinos on the other hand is almost independent of $\delta_{CP}$. The 50 kton magnetized Iron CALorimeter at the India-based Neutrino Observatory (ICAL@INO) will be observing atmospheric neutrinos. The charge identification capability of this detector gives it an edge over others for mass hierarchy determination through observation of earth matter effects. We study in detail the neutrino mass hierarchy sensitivity of the data from this experiment simulated using the Nuance based generator developed for ICAL@INO and folded with the detector resolutions and efficiencies obtained by the INO collaboration from a full Geant4-based detector simulation. The data from ICAL@INO is then combined with simulated data from T2K, NOvA, Double Chooz, RENO and Daya Bay experiments and a combined sensitivity study to the mass hierarchy is performed. With 10 years of ICAL@INO data combined with T2K, NOvA and reactor data, one could get about $2.3\sigma-5.7\sigma$ discovery of the neutrino mass hierarchy, depending on the true value of $\sin^2\theta_{23}$ [0.4 -- 0.6], $\sin^22\theta_{13}$ [0.08 -- 0.12] and $\delta_{CP}$ [0 -- 2$\pi$].

Compatibility of θ 13 and the Type I seesaw model with A 4 symmetry

Abstract We derive formulae for neutrino masses and mixing angles in a type I seesaw framework with an underlying A 4 flavor symmetry. In particular, the Majorana neutrino mass matrix includes contributions from an A 4 triplet, 1, 1′, and 1′′ flavon fields. Using these formulae, we constrain the general A 4 parameter space using the updated global fits on neutrino mixing angles and mass squared differences, including results from the Daya Bay and RENO experiments, and we find predictive relations among the mixing parameters for certain choices of the triplet vacuum expectation value. In the normal hierarchy case, sizable deviation from maximal atmospheric mixing is predicted, and such deviation is strongly correlated with the value of θ13 in the range of ~ (8 − 10)◦. On the other hand, such deviation is negligible and insensitive to θ13 in the inverted mass hierarchy case. We also show expectations for the Dirac CP phase resulting from the parameter scan. Future refined measurements of neutrino mixing angles will test these predicted correlations and potentially show evidence for particular triplet vev patterns.

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.

A supersymmetricSU(5)×T′unified model of flavor with largeθ13

We present a SUSY SU(5)xT' unified flavour model with type I see-saw mechanism of neutrino mass generation, which predicts the reactor neutrino angle to be \theta_{13} = 0.14 close to the recent results from the Daya Bay and RENO experiments. The model predicts also values of the solar and atmospheric neutrino mixing angles, which are compatible with the existing data. The T' breaking leads to tri-bimaximal mixing in the neutrino sector, which is perturbed by sizeable corrections from the charged lepton sector. The model exhibits geometrical CP violation, where all complex phases have their origin from the complex Clebsch-Gordan coefficients of T'. The values of the Dirac and Majorana CP violating phases are predicted. For the Dirac phase in the standard parametrisation of the neutrino mixing matrix we get a value close to 90 degrees \delta = \pi/2 - 0.45 \theta^c = 84.3 degrees, \theta^c being the Cabibbo angle. The neutrino mass spectrum can be with normal ordering (2 cases) or inverted ordering. In each case the values of the three light neutrino masses are predicted with relatively small uncertainties, which allows to get also unambiguous predictions for the neutrino-less double beta decay effective Majorana mass.

Nonzeroθ13andCPviolation in a model withA4flavor symmetry

Motivated by recent observations of non-zero $\theta_{13}$ from the Daya Bay and RENO experiments, we propose a renormalizable neutrino model with $A_4$ discrete symmetry accounting for deviations from the tri-bimaximal mixing pattern of neutrino mixing matrix indicated by neutrino oscillation data. In the model, the light neutrino masses can be generated by radiative corrections, and we show how the light neutrino mass matrix can be diagonalized by the Pontecorvo-Maki-Nakagawa-Sakata mixing matrix whose entries are determined by the current neutrino data including the Daya Bay result. We show that the origin of the deviations from the TBM mixing is non-degeneracy of the neutrino Yukawa coupling constants, and unremovable CP phases in the neutrino Yukawa matrix give rise to both low energy CP violation measurable from neutrino oscillation and high energy CP violation.

Global status of neutrino oscillation parameters after Neutrino-2012

Here we update the global fit of neutrino oscillations in arXiv:1103.0734 and arXiv:1108.1376 including the recent measurements of reactor antineutrino disappearance reported by the Double Chooz, Daya Bay and RENO experiments, together with latest MINOS and T2K appearance and disappearance results, as presented at the Neutrino-2012 conference. We find that the preferred global fit value of $\theta_{13}$ is quite large: $\sin^2\theta_{13} \simeq 0.025$ for normal and inverted neutrino mass ordering, with $\theta_{13} = 0$ now excluded at more than 10$\sigma$. The impact of the new $\theta_{13}$ measurements over the other neutrino oscillation parameters is discussed as well as the role of the new long-baseline neutrino data and the atmospheric neutrino analysis in the determination of a non-maximal atmospheric angle $\theta_{23}$.

Impacts of the observedθ13on the running behaviors of Dirac and Majorana neutrino mixing angles andCP-violating phases

The recent observation of the smallest neutrino mixing angle $\theta_{13}$ in the Daya Bay and RENO experiments motivates us to examine whether $\theta_{13} \simeq 9^\circ$ at the electroweak scale can be generated from $\theta_{13} = 0^\circ$ at a superhigh-energy scale via the radiative corrections. We find that it is difficult but not impossible in the minimal supersymmetric standard model (MSSM), and a relatively large $\theta_{13}$ may have some nontrivial impacts on the running behaviors of the other two mixing angles and CP-violating phases. In particular, we demonstrate that the CP-violating phases play a crucial role in the evolution of the mixing angles by using the one-loop renormalization-group equations of the Dirac or Majorana neutrinos in the MSSM. We also take the "correlative" neutrino mixing pattern with $\theta_{12} \simeq 35.3^\circ$, $\theta_{23} = 45^\circ$ and $\theta_{13} \simeq 9.7^\circ$ at a presumable flavor symmetry scale as an example to illustrate that the three mixing angles can receive comparably small radiative corrections and thus evolve to their best-fit values at the electroweak scale if the CP-violating phases are properly adjusted.

Perturbative generation ofθ13from tribimaximal neutrino mixing

Solar and atmospheric neutrino oscillations are consistent with a tribimaximal form of the mixing matrix $U$ of the lepton sector. Exact tribimaximal mixing leads to $\theta_{13}=0$. Recent results from the Daya Bay and RENO experiments have established a non-zero value of $\theta_{13}$. Keeping the leading behaviour of $U$ as tribimaximal we perform a model-independent perturbative calculation to incorporate a non-vanishing $\theta_{13}$. We identify the nature of the perturbation matrix and consider the possibility of the solar neutrino splitting also resulting from it. We calculate up to first order in perturbation theory and evaluate the deviations proportional to $\sin \theta_{13}$ while including CP-nonconservation. Finally, we briefly discuss a gauge model where such an addition to the neutrino mass matrix arises through one-loop effects.

Understanding the performance of the low-energy neutrino factory: The dependence on baseline distance and stored-muon energy

We study the physics reach of a low-energy neutrino factory (LENF) and its dependence on the chosen baseline distance, $L$, and stored-muon energy, ${E}_{\ensuremath{\mu}}$, in order to ascertain the configuration of the optimal LENF. In particular, we study the performance of the LENF over a range of baseline distances from 1000 km to 4000 km and stored-muon energies from 4 GeV to 25 GeV, connecting the early studies of the LENF (1300 km, 4.5 GeV) to those of the conventional, high-energy neutrino factory design (4000 km and 7000 km, 25 GeV). Three different magnetized detector options are considered: a Totally-Active Scintillator Detector (TASD) and two models of a liquid-argon detector distinguished by optimistic and conservative performance estimates. In order to compare the sensitivity of each set-up, we compute the full $\ensuremath{\delta}$-dependent discovery contours for the determination of ${\ensuremath{\theta}}_{13}\ensuremath{\ne}0$, ${\ensuremath{\delta}}_{CP}\mathrm{\ensuremath{\in}\ensuremath{\llap{\not\;}}}{0,\ensuremath{\pi}}$ and $\mathrm{sign}(\ensuremath{\Delta}{m}_{13}^{2})$. For large values of ${\ensuremath{\theta}}_{13}$, as recently confirmed by the Daya Bay and RENO experiments, the LENF provides a strong discovery potential over the majority of the $L\mathrm{\text{\ensuremath{-}}}{E}_{\ensuremath{\mu}}$ parameter space and is a promising candidate for the future generation of long baseline experiments aimed at discovering $CP$-violation and the mass hierarchy, and at making a precise determination of the oscillation parameters.

Addendum: Neutrino mass hierarchy determination using reactor antineutrinos

We update our study of neutrino mass hierarchy determination using a high statistics reactor electron anti-neutrino experiment in the light of the recent evidences of a relatively large non-zero value of \theta_{13} from the Daya Bay and RENO experiments. We find that there are noticeable modifications in the results, which allow a relaxation in the detector's characteristics, such as the energy resolution and exposure, required to obtain a significant sensitivity to, or to determine, the neutrino mass hierarchy in such a reactor experiment.

Neutrino Mass Hierarchy and Octant Determination with Atmospheric Neutrinos

The recent discovery by the Daya-Bay and RENO experiments, that θ(13) is nonzero and relatively large, significantly impacts existing experiments and the planning of future facilities. In many scenarios, the nonzero value of θ(13) implies that θ(23) is likely to be different from π/4. Additionally, large detectors will be sensitive to matter effects on the oscillations of atmospheric neutrinos, making it possible to determine the neutrino mass hierarchy and the octant of θ(23). We show that a 50 kT magnetized liquid argon neutrino detector can ascertain the mass hierarchy with a significance larger than 4σ with moderate exposure times, and the octant at the level of 2-3σ with greater exposure.

Experimental bounds on sterile neutrino mixing angles

Abstract We derive bounds on the mixing between the Standard Model (“active”) neutrinos and their right-chiral (“sterile”) counterparts in the see-saw models, by combining neutrino oscillation data and results of direct experimental searches. We demonstrate that the mixing of sterile neutrinos with any active flavour can be significantly suppressed for the values of the angle θ 13 measured recently by Daya Bay and RENO experiments. We reinterpret the results of searches for sterile neutrinos by the PS191 and CHARM experiments, considering not only charged current but also neutral current-mediated decays, as applicable in the case of see-saw models. The resulting lower bounds on sterile neutrino lifetime are up to an order of magnitude stronger than previously discussed in the literature. Combination of these results with the upper bound on the lifetime coming from primordial nucleosynthesis rule out the possibility that two sterile neutrinos with the masses between 10 MeV and the pion mass are solely responsible for neutrino flavour oscillations. We discuss the implications of our results for the Neutrino Minimal Standard Model (the νMSM).

Observation of Reactor Electron Antineutrinos Disappearance in the RENO Experiment

The RENO experiment has observed the disappearance of reactor electron antineutrinos, consistent with neutrino oscillations, with a significance of 4.9 standard deviations. Antineutrinos from six 2.8 GW(th) reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 and 1383 m, respectively, from the reactor array center. In the 229 d data-taking period between 11 August 2011 and 26 March 2012, the far (near) detector observed 17102 (154088) electron antineutrino candidate events with a background fraction of 5.5% (2.7%). The ratio of observed to expected numbers of antineutrinos in the far detector is 0.920±0.009(stat)±0.014(syst). From this deficit, we determine sin(2)2θ(13)=0.113±0.013(stat)±0.019(syst) based on a rate-only analysis.

Combining accelerator and reactor measurements of θ 13: the first result

Abstract The lepton mixing angle θ 13, the only unknown angle in the standard three-flavor neutrino mixing scheme, is finally measured by the recent reactor and accelerator neutrino experiments. We perform a combined analysis of the data coming from T2K, MINOS, Double Chooz, Daya Bay and RENO experiments and find sin2 2θ 13 = 0.096 ± 0.013(±0.040) at 1 σ (3 σ) CL and that the hypothesis θ 13 = 0 is now rejected at a significance level of 7.7 σ. We also discuss the near future expectation on the precision of the θ 13 determination by using expected data from these ongoing experiments.

Common origin ofμ−τandCPbreaking in the neutrino seesaw, baryon asymmetry, and hidden flavor symmetry

We conjecture that all $CP$ violations (both Dirac and Majorana types) arise from a common origin in the neutrino seesaw. With this conceptually attractive and simple conjecture, we deduce that $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ breaking shares the common origin with all $CP$ violations. We study the common origin of $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ and $CP$ breaking in the Dirac mass matrix of seesaw Lagrangian (with right-handed neutrinos being $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ blind), which uniquely leads to inverted mass ordering of light neutrinos. We then predict a very different correlation between the two small $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ breaking observables ${\ensuremath{\theta}}_{13}\ensuremath{-}0\ifmmode^\circ\else\textdegree\fi{}$ and ${\ensuremath{\theta}}_{23}\ensuremath{-}45\ifmmode^\circ\else\textdegree\fi{}$, which can saturate the present experimental upper limit on ${\ensuremath{\theta}}_{13}$. This will be tested against our previous normal mass-ordering scheme by the ongoing oscillation experiments. We also analyze the correlations of ${\ensuremath{\theta}}_{13}$ with Jarlskog invariant and neutrinoless $\ensuremath{\beta}\ensuremath{\beta}$-decay observable. From the common origin of $CP$ and $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ breaking in the neutrino seesaw, we establish a direct link between the low energy $CP$ violations and the cosmological $CP$ violation for baryon asymmetry. With these we further predict a lower bound on ${\ensuremath{\theta}}_{13}$, supporting the ongoing probes of ${\ensuremath{\theta}}_{13}$ at Daya Bay, Double Chooz, and RENO experiments. Finally, we analyze the general model-independent ${\mathbb{Z}}_{2}\ensuremath{\bigotimes}{\mathbb{Z}}_{2}$ symmetry structure of the light neutrino sector, and map it into the seesaw sector, where one of the ${\mathbb{Z}}_{2}$'s corresponds to the $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ symmetry ${\mathbb{Z}}_{2}^{\ensuremath{\mu}\ensuremath{\tau}}$ and another the hidden symmetry ${\mathbb{Z}}_{2}^{s}$ (revealed in our previous work) which dictates the solar mixing angle ${\ensuremath{\theta}}_{12}$. We derive the physical consequences of this ${\mathbb{Z}}_{2}^{s}$ and its possible partial violation in the presence of $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ breaking (with or without the neutrino seesaw), regarding the ${\ensuremath{\theta}}_{12}$ determination and the correlation between $\ensuremath{\mu}\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ breaking observables.

Prospects of reactor neutrino experiments

Since the energy of a reactor neutrino is a few MeV, all Δ m 12 2 , Δ m 23 2 and Δ m 13 2 oscillations are accessible by reactor neutrino experiments. KamLAND observed the Δ m 12 2 oscillation and currently Double Chooz, RENO and Dayabay experiments are under construction aiming to detect Δ m 13 2 + Δ m 23 2 oscillation. There are still good prospects for future reactor neutrino experiments after them. For example, there is room to further improve sin 2 2 θ 13 accuracy at a baseline of ∼1.5 km, a very precise sin 2 2 θ 12 measurement and the determination of mass hierarchy may be possible at a baseline ∼50 km, and if KamLAND is enlarged to the SuperKamiokande size, better measurement of Δ m 12 2 and sin 2 2 θ 12 will be anticipated. It is important to take into account such possibilities when planning future neutrino program after θ 13 is measured by current experiments.

RENO: reactor experiment for neutrino oscillation at Yonggwang

The RENO experiment is under construction to measure the value of the smallest and unknown neutrino mixing angle θ13. The experiment will compare the measured fluxes of electron antineutrinos at two detectors located at 290 m and 1.4 km distances from the center of the Yonggwang nuclear reactors in Korea. It is planned to start data-taking in early 2010. An estimated systematic uncertainty associated with the measurement is less than 0.6%. With three years of data, the experiment will search for the mixing angle values of sin22θ13 down to 0.02.

A unified analysis of the reactor neutrino program towards the measurement of the θ13 mixing angle

We presented a detailed quantitative discussion of the measurement of the leptonic mixing angle θ13 through currently scheduled reactor neutrino oscillation experiments. We focussed on Double Chooz (Phase I & II), Daya Bay (Phase I & II) and RENO experiments. We performed a unified analysis, including systematics, backgrounds and accurate experimental setup in each case. Each identified systematical uncertainty and background impact has been assessed on experimental setups following published data when available and extrapolating from Double Chooz acquired knowledge otherwise. We sum up, here, a new common analysis of their sensitivities to sin2(2θ13) and study the impact of the different systematics based on the pulls approach. Through this generic statistical analysis we discuss the advantages and drawbacks of each experimental setup.

Using the Google Search Appliance for Federated Searching

This article discusses the University of Nevada, Reno's experiment of federated searching with version 4.1 of the Google Search Appliance. The project's testbed included locally held CONTENTdm and geospatial data collections and a sample of records from EBSCO's Academic Search Premiere database. The latter set of records revealed the GSA's limitations in being able to index and retrieve content that is dynamically generated and that requires third party authentication.