Reactor Neutrino Oscillation Experiments Research Articles

Decoherence effects in reactor and Gallium neutrino oscillation experiments: a QFT approach

We adopt the quantum field theoretical method to calculate the amplitude and event rate for a neutrino oscillation experiment, considering neutrino production, propagation and detection as a single process. This method allows to take into account decoherence effects in the transition amplitude induced by the quantum mechanical uncertainties of all particles involved in the process. We extend the method to include coherence loss due to interactions with the environment, similar to collisional line broadening. In addition to generic decoherence induced at the amplitude level, the formalism allows to include, in a straightforward way, additional damping effects related to phase-space integrals over momenta of unobserved particles as well as other classical averaging effects. We apply this method to neutrino oscillation searches at reactor and Gallium experiments and confirm that quantum decoherence is many orders of magnitudes smaller than classical averaging effects and therefore unobservable. The method used here can be applied with minimal modifications also to other types of oscillation experiments, e.g., accelerator based beam experiments.

Damping signatures at JUNO, a medium-baseline reactor neutrino oscillation experiment

We study damping signatures at the Jiangmen Underground Neutrino Observatory (JUNO), a medium-baseline reactor neutrino oscillation experiment. These damping signatures are motivated by various new physics models, including quantum decoherence, ν3 decay, neutrino absorption, and wave packet decoherence. The phenomenological effects of these models can be characterized by exponential damping factors at the probability level. We assess how well JUNO can constrain these damping parameters and how to disentangle these different damping signatures at JUNO. Compared to current experimental limits, JUNO can significantly improve the limits on τ3/m3 in the ν3 decay model, the width of the neutrino wave packet σx, and the intrinsic relative dispersion of neutrino momentum σrel.

Combined analysis of neutrino decoherence at reactor experiments

Reactor experiments are well suited to probe the possible loss of coherence of neutrino oscillations due to wave-packets separation. We combine data from the short-baseline experiments Daya Bay and the Reactor Experiment for Neutrino Oscillation (RENO) and from the long baseline reactor experiment KamLAND to obtain the best current limit on the reactor antineutrino wave-packet width, σ > 2.1 × 10−4 nm at 90% CL. We also find that the determination of standard oscillation parameters is robust, i.e., it is mostly insensitive to the presence of hypothetical decoherence effects once one combines the results of the different reactor neutrino experiments.

Studying the neutrino wave-packet effects at medium-baseline reactor neutrino oscillation experiments and the potential benefits of an extra detector

We examine the potential of the future medium-baseline reactor neutrino oscillation (MBRO) experiments in studying neutrino wave-packet impact. In our study, we treat neutrinos as wave packets and use the corresponding neutrino flavor transition probabilities. The delocalization, separation and spreading of the wave packets lead to decoherence and dispersion effects, which modify the plane-wave neutrino oscillation pattern, by amounts that depend on the energy uncertainties in the initial neutrino wave packets. We find that MBRO experiments could be sensitive to the wave-packet impact, since the baseline is long enough and also the capability of observing small corrections to the neutrino oscillations due to excellent detector energy resolution. Besides studying the constraints on the decoherence parameter, we also examine the potential wave-packet impacts on the precision of measuring θ12 and other oscillation parameters in the future medium-baseline reactor neutrino oscillation experiments. Moreover, we also probe the potential benefits of an additional detector for studying such exotic neutrino physics.

Global oscillation data analysis on the 3\u03bd mixing without unitarity

We present results of a combined analysis in neutrino oscillations without unitarity assumption in the 3ν mixing picture. Constraints on neutrino mixing matrix elements are based on recent data from the reactor, solar and long-baseline accelerator neutrino oscillation experiments. The current data are consistent with the standard 3ν scheme. The precision on different matrix elements can be as good as a few percent at 3σ CL, and is mainly limited by the experimental statistical uncertainty. The νe related elements are the most precisely measured among all sectors with the uncertainties < 20%. The measured leptonic CP violation is very close to the one assuming the standard 3ν mixing. The deviations on normalization and the unitarity triangle closure are confined within mathcal{O} (10−3), mathcal{O} (10−2) and mathcal{O} (10−1), for νe, νμ and ντ sectors, respectively. We look forward to the next-generation neutrino oscillation experiments such as DUNE, T2HK, and JUNO, especially the precision measurements on ντ oscillations, to significantly improve the precision of unitarity test on the 3ν mixing matrix.

Potential impact of sub-structure on the determination of neutrino mass hierarchy at medium-baseline reactor neutrino oscillation experiments

In the past decade, the precise measurement of the lastly known neutrino mixing angle theta _{13} has enabled the resolution of neutrino mass hierarch (MH) at medium-baseline reactor neutrino oscillation (MBRO) experiments. Recent calculations of the reactor neutrino flux predict percent-level sub-structures in the bar{nu }_e spectrum due to Coulomb effects in beta decay. Such fine structure in the reactor spectrum has been an issue of concern for efforts to determine the neutrino MH for the MBRO approach, the concern being that the sub-dominant oscillation pattern used to discriminate different hierarchies will be obscured by fine structure. The energy resolutions of current reactor experiments are not sufficient to measure such fine structure, and therefore the size and location in energy of these predicted discontinuities has not been confirmed experimentally. There has been speculation that a near detector is required with sufficient energy resolution to resolve the fine structure. This article studies the impact of fine structure on the resolution of MH, based on predicted reactor neutrino spectra, using the measured spectrum from Daya Bay as a reference. We also investigate how a near detector could improve the sensitivity of neutrino MH resolution based on various assumptions of near detector energy resolution.

The sensitivity to electron antineutrinos from the binary neutron star systems at medium-baseline reactor neutrino oscillation experiment(s)

After gravitational wave (GW) transients were first observed in 2015, searching for the coincident neutrinos has become one of the most important missions at the current neutrino experiments. Particularly, the coincident searches draw more and more attentions after one GW candidate (denoted GW170817) was detected, which was the first sign of a production of a binary neutron star (BNS) merger. However, no candidate neutrinos have been found yet. As a prospective study, this article presents a search for the potential electron antineutrinos (ν¯e) from BNS mergers in future medium-baseline reactor neutrino oscillation (MBRO) experiment(s). On one hand, we examine the detection sensitivity to the ν¯e signals from BNS mergers at future MBRO experiment(s). On the other hand, we convert the ν¯e signal sensitivity to the ν¯e fluence upper limits and evaluate the furthest detectable distances for BNS mergers based on the evolution models describing the process of neutrino emission. Moreover, we also analyze the improvement of sensitivity and the enhancement of detectable distance with a proposed extra detector at future MBRO experiment(s).

Probing neutrino quantum decoherence at reactor experiments

We explore how well reactor antineutrino experiments can constrain or measure the loss of quantum coherence in neutrino oscillations. We assume that decoherence effects are encoded in the size of the neutrino wave-packet, σ. We find that the current experiments Daya Bay and the Reactor Experiment for Neutrino Oscillation (RENO) already constrain σ > 1.0×10−4 nm and estimate that future data from the Jiangmen Underground Neutrino Observatory (JUNO) would be sensitive to σ < 2.1 × 10−3 nm. If the effects of loss of coherence are within the sensitivity of JUNO, we expect σ to be measured with good precision. The discovery of nontrivial decoherence effects in JUNO would indicate that our understanding of the coherence of neutrino sources is, at least, incomplete.

Observation of reactor antineutrino disappearance using delayed neutron capture on hydrogen at RENO

The Reactor Experiment for Neutrino Oscillation (RENO) experiment has been taking data using two identical liquid scintillator detectors since August 2011. The experiment has observed the disappearance of reactor neutrinos in their interactions with free protons, followed by neutron capture on hydrogen (n-H). Based on 1500 live days of data taken with 16.8 GWth reactors at the Hanbit Nuclear Power Plant in Korea, the near (far) detector observes 567690 (90747) electron antineutrino candidate events with the n-H data. This provides an independent measurement of neutrino mixing angle θ13 and a consistency check on the validity of the result obtained from the data with neutron capture on Gadolinium (n-Gd). Furthermore, it provides an important cross-check on the systematic uncertainties of the n-Gd measurement. Based on a rate-only analysis, we obtain sin2 2θ13 = 0.086 ± 0.008(stat.) ± 0.014(syst.). The combination of this result with that of n-Gd is also reported.

New Results from RENO using 1500 Days of Data

RENO (Reactor Experiment for Neutrino Oscillation) is the first reactor neutrino experiment which began data-taking in 2011 with two identical near and far detectors in Yonggwang, Korea. Using 1500 live days of data, sin22θ13 and |Δm2ee| are updated using spectral measurements: sin22θ13 = 0.086 ± 0.006 (stat.) ± 0.005 (syst.) and |Δm2ee| = 2.61+015-016 (stat.) ± 0.09 (syst.) (×10−3 eV2). The correlation between the 5 MeV excess rate and the reactor thermal power is again clearly observed with the increased data set.

Recent Result from RENO

The Reactor Experiment for Neutrino Oscillation (RENO) started data-taking from August, 2011 and has measured the smallest neutrino mixing angle θ13 by observing the disappearance of reactor antineutrinos. Antineutrinos from the six reactors at Hanbit Nuclear Power Plant in Korea are detected and compared by the two identical detectors located in the near and far distances from the reactor array center. We present recent results on precisely measured sin22θ13 value and based on spectral analysis using the 500 days of data sample, which are taken from August, 2011 to Jan, 2013.

Analysis of reactor-neutrino oscillation experiment based on consideration of internal constituent motion

Analysis of reactor-neutrino oscillation experiment based on consideration of internal constituent motion

Spectral measurement of the electron antineutrino oscillation amplitude and frequency using 500 live days of RENO data

The Reactor Experiment for Neutrino Oscillation (RENO) has been taking electron antineutrino ($\overline{\nu}_{e}$) data from the reactors in Yonggwang, Korea, using two identical detectors since August 2011. Using roughly 500 live days of data through January 2013 we observe 290,775 (31,514) reactor $\overline{\nu}_{e}$ candidate events with 2.8 (4.9)% background in the near (far) detector. The observed visible positron spectra from the reactor $\overline{\nu}_{e}$ events in both detectors show discrepancy around 5 MeV with regard to the prediction from the current reactor $\overline{\nu}_{e}$ model. Based on a far-to-near ratio measurement using the spectral and rate information we have obtained $\sin^2 2 \theta_{13} = 0.082 \pm 0.009({\rm stat.}) \pm 0.006({\rm syst.})$ and $|\Delta m_{ee}^2| =[2.62_{-0.23}^{+0.21}({\rm stat.})_{-0.13}^{+0.12}({\rm syst.})]\times 10^{-3}$eV$^2$.

Neutrino parameters from reactor and accelerator neutrino experiments

We revisit correlations of neutrino oscillation parameters in reactor and long-baseline neutrino oscillation experiments. A framework based on an effective value of ${\ensuremath{\theta}}_{13}$ is presented, which can be used to analytically study the correlations and explain some questions including why and when ${\ensuremath{\delta}}_{CP}$ has the best fit value of $\ensuremath{-}\ensuremath{\pi}/2$, why current and future long-baseline experiments will have less precision of ${\ensuremath{\delta}}_{CP}$ around $\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}/2$ than that around zero, etc. Recent hints on the $CP$ phase are then considered from the point of view that different reactor and long-baseline neutrino experiments provide currently different best-fit values of ${\ensuremath{\theta}}_{13}$ and ${\ensuremath{\theta}}_{23}$. We point out that the significance of the hints changes for the different available best-fit values.

Mass problem in the Standard Model

We propose a new SU(3)C ⊗ SU(2)L ⊗ U(1)Y ⊗ U(1)X gauge model which is non universal respect to the three fermion families of the Standard Model. We introduce additional one top-like quark, two bottom-like quarks and three right handed neutrinos in order to have an anomaly free theory. We also consider additional three right handed neutrinos which are singlets respect to the gauge symmetry of the model to implement see saw mechanism and give masses to the light neutrinos according to the neutrino oscillation phenomenology. In the context of this horizontal gauge symmetry we find mass ansatz for leptons and quarks. In particular, from the analysis of solar, atmospheric, reactor and accelerator neutrino oscillation experiments, we get the allow region for the Yukawa couplings for the charge and neutral lepton sectors according with the mass squared differences and mixing angles for the two neutrino hierarchy schemes, normal and inverted.

Precise measurement of reactor antineutrino spectrum flux and spectrum at RENO

The RENO(Reactor Experiment for Neutrino Oscillation) experiment is to measure the smallest neutrino mixing angle theta13 using anti-neutrinos emitted from the Hanbit nuclear power plant in Korea. It is essential to compare the observed and expected fluxes of reactor antineutrinos for determining the neutrino disappearance probability. The expected reactor neutrino flux is calculated from the reactor thermal power and the fission rate of individual fuel isotope. Time-dependent fuel composition changes not only neutrino fluxes but also it distort the antineutrino spectrum. In this presentation, we describe how to derive the expected reactor neutrino fluxes and spectrum at both near and far detectors and report an excess in the observed spectrum near 5 MeV at RENO.

Prompt energy calibration at RENO

RENO (Reactor Experiment for Neutrino Oscillation) has obtained the first measured value of effective neutrino mass difference from a spectral analysis of reactor neutrino disappearance. The measurement absolutely relies on the accurate energy calibration. Several radioactive sources such as 137Cs, 54Mn, 68Ge, 65Zn, 60Co, Po-Be, Am-Be, and Cf-Ni, are used for the energy calibration of the RENO detectors. We obtained an energy conversion function from observed charges to prompt signal energy which describes a non-linear response due to the quenching effect in liquid scintillator and Cherenkov radiation. We have verified the performance of the energy calibration using copious betadecay events from radioactive isotopes B12 that are produced by cosmic-muon interaction. The energy calibration was performed for the target and gamma-catcher regions separately due to their different energy responses. In this presentation we describe the methods and results of the energy calibration.

New results from RENO & prospects with RENO-50

This paper briefly describes recent progress of RENO and next generation future prospect of the reactor neutrino oscillation experiment, RENO-50. Recently the RENO experiment has updated its latest value on sin22θ13 and provided new results on 5 MeV excess, Δm2ee, θ13 with n-H analysis, absolute antineutrino flux measurement, and sterile neutrino search. It gives rich programs of neutrino properties, detector development, nuclear monitoring and application. Using reactor neutrinos, the future RENO-50 experiment will search for more precise measurement of θ12, Δm212 and mass hierarchy.

Wave-packet treatment of reactor neutrino oscillation experiments and its implications on determining the neutrino mass hierarchy

We derive the neutrino flavor transition probabilities with the neutrino treated as a wave packet. The decoherence and dispersion effects from the wave-packet treatment show up as damping and phase-shifting of the plane-wave neutrino oscillation patterns. If the energy uncertainty in the initial neutrino wave packet is larger than around 0.01 of the neutrino energy, the decoherence and dispersion effects would degrade the sensitivity of reactor neutrino experiments to mass hierarchy measurement to lower than 3 $\sigma$ confidence level.

Recent result from RENO

The Reactor Experiment for Neutrino Oscillation (RENO) started data-taking from August, 2011 and has measured the smallest neutrino mixing angle θ13 by observing the disappearance of reactor antineutrinos. Antineutrinos from the six reactors at Hanbit Nuclear Power Plant in Korea are detected and compared by the two identical detectors located in the near and far distances from the reactor array center. We present new results on precisely measured sin22θ13 value and |Δm2ee| based on spectral analysis using the 800 days of data sample, which are taken from August, 2011 to Dec., 2013.