Reactor Electron Antineutrinos Research Articles

Neutrino mass ordering determination through combined analysis with JUNO and KM3NeT/ORCA

The determination of neutrino mass ordering (NMO) is one of the prime goals of several neutrino experiments. KM3NeT/ORCA and JUNO are two next-generation neutrino oscillation experiments both aiming at addressing this question. ORCA can determine the NMO by probing Earth matter effects on the oscillation of atmospheric neutrinos in the GeV energy range. JUNO, on the other hand, is sensitive to the NMO by investigating the interference effects of fast oscillations in the reactor electron antineutrino spectrum at medium baseline. This contribution presents the potential of determining the NMO through a combined analysis of JUNO and ORCA data. When measuring the Δm312 with a wrong ordering assumption, the best-fit values are different between the two experiments. This tension, together with good constraints on the Δm312 measurement by both experiments, enhances the combined NMO sensitivity beyond the simple sum of their sensitivities. The analysis shows that a 5 σ significance is reachable in less than 2 years of data taking with both experiments for true normal neutrino mass ordering, assuming current global best-fit values of the oscillation parameters, while 6 years will be needed for any other parameter set.

Using the Two-Phase Emission Detector RED-100 at NPP to Study Coherent Elastic Neutrinos Scattering off Nuclei

The two-phase emission detector RED-100 with 130 kg of liquid xenon as a working medium has been exhibited at a distance of 19 m from the core of the VVER-1000/320 nuclear power reactor at the fourth power unit of the Kalinin Nuclear Plant Power in 2021–2022. Due to the high sensitivity of the detector for weak ionization signals (down to single electrons), the detector has been used to search for the elastic coherent scattering of reactor electron antineutrinos off xenon nuclei. However, the observation of ~30 kHz single-electron noise did not quite allow for an effective selection of the useful events. The next experiment with the RED-100 detector is considered to be arranged with 62 kg of liquid argon as a working medium. The advantages of this approach are discussed in this paper.

Exploring coherent elastic neutrino-nucleus scattering using reactor electron antineutrinos in the NEON experiment

Neutrino elastic scattering observation with NaI (NEON) is an experiment designed to detect neutrino-nucleus coherent scattering using reactor electron antineutrinos. NEON is based on an array of six NaI(Tl) crystals with a total mass of 13.3 kg, located at the tendon gallery that is 23.7 m away from a reactor core with a thermal power of 2.8 GW in the Hanbit nuclear power complex. The installation of the NEON detector was completed in December 2020, and since May 2021, the detector has acquired data at full reactor power. Based on the observed light yields of the NaI crystals of approximately 22, number of photoelectrons per unit keV electron-equivalent energy (keVee), and 6 counts/kg/keV/day background level at 2–6 keVee energy, coherent elastic neutrino-nucleus scattering (CEnu NS) observation sensitivity is evaluated as more than 3sigma assuming 1-year reactor-on and 100 days reactor-off data, 0.2 keVee energy threshold, and 7 counts/keV/kg/day background in the signal region of 0.2-0.5 keVee. This paper describes the design of the NEON detector, including the shielding arrangement, configuration of NaI(Tl) crystals, and associated operating systems. The initial performance and associated sensitivity of the experiment are also presented.

ERNIE: A reactor antineutrino inverse beta decay event generator

We present ERNIE, a computer program which generates nuclear reactor electron antineutrinos and inverse beta decay events induced by these particles, using the Monte-Carlo method. The program allows the usage of different antineutrino energy spectra models and can simulate the time evolution of the overall antineutrino spectrum because of the burn-up effect. The output of the program can readily be used in detector simulations made with e.g. GEANT 4. Program summaryProgram Title: ERNIECPC Library link to program files:https://doi.org/10.17632/grk8256yr6.1Developer's repository link:https://github.com/murataltinli/ERNIELicensing provisions: GNU General Public License 3Programming language: C++External libraries: ROOT, HepMC3Nature of problem: Simulations are an important tool in designing and operating particle detectors. Reactor neutrino detector simulations require accurate simulations of the neutrinos emitted by nuclear reactors and their interactions with the detectors. Such a neutrino simulation must allow for the usage of different energy spectra and the time evolution of the neutrino flux due to the burn-up effect. Currently, there is no publicly available software to fulfill these tasks.Solution method: Our program generates reactor neutrinos and inverse beta decay events using Monte-Carlo method. The program features various neutrino energy spectrum models, also allowing usage of user defined models. The time evolution of neutrino flux can be modeled with two different methods. The program exports the generated data in formats commonly used in particle physics studies, and hence the data can readily be used.

Measurement of reactor antineutrino flux and spectrum at RENO

The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos\,($\overline{\nu}_e$) from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966\,094\,(116\,111)\,$\overline{\nu}_e$ candidate events with a background fraction of 2.39\%\,(5.13\%), acquired in the near\,(far) detector, from August 2011 to March 2020. The inverse beta decay (IBD) yield is measured as (5.852$\,\pm\,$0.124$) \times 10^{-43}$\,cm$^2$/fission, corresponding to 0.941\,$\pm$ 0.019 of the prediction by the Huber and Mueller (HM) model. A reactor $\overline{\nu}_e$ spectrum is obtained by unfolding a measured IBD prompt spectrum. The obtained neutrino spectrum shows a clear excess around 6\,MeV relative to the HM prediction. The obtained reactor $\overline{\nu}_e$ spectrum will be useful for understanding unknown neutrino properties and reactor models. The observed discrepancies suggest the next round of precision measurements and modification of the current reactor $\overline{\nu}_e$ models.

First ground-level laboratory test of the two-phase xenon emission detector RED-100

RED-100 is a two-phase detector for study of coherent elastic scattering of reactor electron antineutrinos off xenon atomic nuclei. The detector contains a total of 200 kg of liquid xenon in a titanium cryostat with 160 kg of xenon in active volume inside a Teflon-made light collection cage associated with electrode system. The active volume is viewed by two arrays of nineteen 3′′-diameter Hamamatsu R11410-20 PMTs assembled in two planes on top and bottom. The electrode system is equipped with an electron shutter (a patented device) to reduce a “spontaneous” single-electron noise. The detector was tested in a ground-level laboratory. The obtained results demonstrate that detection of coherent elastic scattering of reactor antineutrinos off xenon nuclei at Kalinin nuclear power plant with the RED-100 detector is feasible with a threshold of 4 ionization electrons.

Estimating Uncertainties in the Reactor Neutrino Directionality Using Liquid Scintillator with Monte Carlo Simulation

This paper describes in detail the uncertainties due to several factors that may affect the direction vector of a reactor neutrino in a liquid scintillation detector. The reactor neutrino direction vector was reconstructed through a charge weighting method. The paper simulates the response of gadolinium-loaded, liquid scintillator detector to reactor electron anti-neutrinos. The reaction is based on neutrino capture on hydro-genic protons of inverse beta decay process in the scintillator. A Cherenkov radiation detector can reconstruct the directional information of incident neutrinos relatively well, compared to the liquid scintillation detector. Statistics, spatial resolution, neutrino energy, and multi-reactor and multi-detectors are examined by using Monte Carlo simulation based on the cylindrical liquid scintillating detector model. Furthermore, this simulated model is detailed down to the optical processes, and the source of reactor fuel composition. Finally, one of the main goals is to provide the potential of the detector to measure the origin direction of the incident neutrino. Furthermore, our intention is to help understanding of various uncertainties of the neutrino directionality study for the future massive liquid scintillating neutrino detectors.

Fuel-Composition Dependent Reactor Antineutrino Yield at RENO.

We report a fuel-dependent reactor electron antineutrino (ν[over ¯]_{e}) yield using six 2.8 GW_{th} reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses 850 666 ν[over ¯]_{e} candidate events with a background fraction of 2.0% acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel ^{235}U dependent variation of measured IBD yields with a slope of (1.51±0.23)×10^{-43} cm^{2}/fission and measure a total average IBD yield of (5.84±0.13)×10^{-43} cm^{2}/fission. The hypothesis of no fuel-dependent IBD yield is ruled out at 6.6σ. The observed IBD yield variation over ^{235}U isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at 1.3 σ. The measured fuel-dependent variation determines IBD yields of (6.15±0.19)×10^{-43} and (4.18±0.26)×10^{-43} cm^{2}/fission for two dominant fuel isotopes ^{235}U and ^{239}Pu, respectively. The measured IBD yield per ^{235}U fission shows the largest deficit relative to the HM prediction. Reevaluation of the ^{235}U IBD yield per fission may mostly solve the reactor antineutrino anomaly (RAA) while ^{239}Pu is not completely ruled out as a possible contributor to the anomaly. We also report a 2.9 σ correlation between the fractional change of the 5MeV excess and the reactor fuel isotope fraction of ^{235}U.

Upper limits on perturbations of nuclear decay rates induced by reactor electron antineutrinos

We report the results of an experiment conducted near the High Flux Isotope Reactor of Oak Ridge National Laboratory, designed to address the question of whether a flux of reactor-generated electron antineutrinos (ν¯e) can alter the rates of weak nuclear interaction induced decays of 54Mn, 22Na, and 60Co. This experiment has small statistical errors but, when systematic uncertainties are included, has null results. Perturbations greater than one part in 104 are excluded at 95% confidence level in β± decay and electron capture processes, in the presence of an antineutrino flux of 3 × 1012 cm−2s−1. The present experimental methods are applicable to a wide range of radionuclides. Improved sensitivity in future experiments can be anticipated as we continue to better understand and reduce the dominant systematic uncertainties.

Towards a reconstruction of Supernova Neutrino Spectra in JUNO

Observation of supernovae (SN) through their neutrino emission is a fundamental point to understand both SN dynamics and neutrino physical properties. JUNO is a 20kton liquid scintillator detector, under construction in Jiangmen, China. The main aim of the experiment is to determine neutrino mass hierarchy by precisely measuring the energy spectrum of reactor electron antineutrinos. However due to its properties, JUNO has the capability of detecting a high statistics of SN events too. Existing data from SN neutrino consists only of 24 events coming from the SN 1987A,the detection of a SN burst in JUNO at ~ 10kpc will yield ~ 5x103 inverse beta decay (IBD) events from electron antineutrinos, about 1500 from proton elastic scattering (pES) above the threshold of 0.2 MeV, about 400 from electron elastic scattering (eES), plus several hundreds on other CC and NC interaction channels from all neutrino species.

EMF Shielding of One Set of Circular Coils with Slight Distortion

Jiangmen Undergroud Neutrino Observatory (JUNO) is a reactor antineutrino experiment with the main purpose for determining the neutrino mass hierarchy by precisely measuring the energy spectrum of nuclear reactor electron antineutrinos. The JUNO central detector consists of 20 kilotons an organic liquid scintillator filling the spherical CD or acrylic sphere whose diameter is 35.4 meters, surrounded by a water pool, approximately 18, 000 20″ and 25, 000 3″ photomultiplier tubes (PMTs) on the inner CD truss and 2,400 20″ Veto-PMT on the outer CD truss. The PMTs are very sensitive to external magnetic fields, the earth magnetic field (EMF) passing through the PMTs without any shielding would largely reduce the efficiency of the PMTs. In order to minimize the effect of EMF inside the detector, JUNO has been planing to use the DC coils to shield EMF, aiming at the residual EMF to less than 10 % on PMT areas.

Measurement of Reactor Antineutrino Oscillation Amplitude and Frequency at RENO.

The RENO experiment reports more precisely measured values of θ_{13} and |Δm_{ee}^{2}| using ∼2200 live days of data. The amplitude and frequency of reactor electron antineutrino (ν[over ¯]_{e}) oscillation are measured by comparing the prompt signal spectra obtained from two identical near and far detectors. In the period between August 2011 and February 2018, the far (near) detector observed 103 212 (850 666) ν[over ¯]_{e} candidate events with a background fraction of 4.8% (2.0%). A clear energy and baseline dependent disappearance of reactor ν[over ¯]_{e} is observed in the deficit of the measured number of ν[over ¯]_{e}. Based on the measured far-to-near ratio of prompt spectra, we obtain sin^{2}2θ_{13}=0.0896±0.0048(stat)±0.0047(syst) and |Δm_{ee}^{2}|=[2.68±0.12(stat)±0.07(syst)]×10^{-3} eV^{2}.

Measurement of neutrino mixing angle θ13 and mass difference [formula omitted] from reactor antineutrino disappearance in the RENO experiment

RENO (Reactor Experiment for Neutrino Oscillation) made a definitive measurement of the smallest neutrino mixing angle θ13 in 2012, based on the disappearance of reactor electron antineutrinos. The experiment has obtained a more precise value of the mixing angle and the first result on neutrino mass difference Δmee2 from an energy and baseline dependent reactor neutrino disappearance using ∼500 days of data. Based on the ratio of inverse-beta-decay (IBD) prompt spectra measured in two identical far and near detectors, we obtain sin2⁡(2θ13)=0.082±0.009(stat.)±0.006(syst.) and |Δmee2|=[2.62−0.23+0.21(stat.)−0.13+0.12(syst.)]×10−3 eV2. An excess of reactor antineutrinos near 5 MeV is observed in the measured prompt spectrum with respect to the most commonly used models. The excess is found to be consistent with coming from reactors. A successful measurement of θ13 is also made in an IBD event sample with a delayed signal of neutron capture on hydrogen. A precise value of θ13 would provide important information on determination of the leptonic CP phase if combined with a result of an accelerator neutrino beam experiment.

A precise calculation of delayed coincidence selection efficiency and accidental coincidence rate**Supported by Ministry of Science and Technology of China (2013CB834302), National Natural Science Foundation of China (11235006, 11475093), Tsinghua University Initiative Scientific Research Program (2012Z02161), and Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education.

A precise background evaluation model is proposed to address the complex data structure of the delayed coincidence method, which is widely used in reactor electron-antineutrino oscillation experiments. In this model, effects from the muon veto, uncorrelated random background, and background are all studied analytically, simplifying the estimation of the systematic uncertainties of signal efficiency and accidental background rate. The results of the calculations are validated numerically with a number of simulation studies and also applied and validated in the recent Daya Bay hydrogen-capture based oscillation measurement.

Spectral structure of electron antineutrinos from nuclear reactors.

Recent measurements of the positron energy spectrum obtained from inverse beta decay interactions of reactor electron antineutrinos show an excess in the 4 to 6MeV region relative to current predictions. First-principles calculations of fission and beta decay processes within a typical pressurized water reactor core identify prominent fission daughter isotopes as a possible origin for this excess. These calculations also predict percent-level substructures in the antineutrino spectrum due to Coulomb effects in beta decay. Precise measurement of these substructures can elucidate the nuclear processes occurring within reactors. These substructures can be a systematic issue for measurements utilizing the detailed spectral shape.

Reactor and Antineutrino Spectrum Calculations for the Double Chooz First Phase Results

The Double Chooz reactor oscillation experiment is designed to search for a non-vanishing value of the mixing angle θ13. For the first phase of the experiment with only the far detector running, the reactor electron antineutrino flux is normalized via reactor simulation. For this first phase and from its last results, Double Chooz observed an evidence for a reactor electron antineutrino disappearance. In 227.93 days of far detector live time, we obtained sin22θ13=0.109±0.030(stat)±0.025(syst). This result excludes the no-oscillation hypothesis at 99.8% CL.

Reactor antineutrino anomaly with knownθ13

We revisit the reactor antineutrino anomaly using the recent reactor flux independent determination of sizable theta?13 by considering the full set of the absolute reactor electron antineutrino flux measurements. When normalized to the predicted flux of Mueller et al. [1], the new world average, after including results from Palo Verde, Chooz, and Double Chooz, is 0.959 +- 0.009 (experiment uncertainty) +- 0.027 (flux systematics). Including the data with kilometer baseline, the new world average is only about 1.4 sigma lower than the unity, weakening the significance of the reactor antineutrino anomaly. The upcoming results from Daya Bay, RENO, and the Double Chooz will provide further information about this issue.

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.

Indication of Reactorν¯eDisappearance in the Double Chooz Experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GWth reactors. The results were obtained from a single 10 m3 fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin22θ13. Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin22θ13=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017<sin22θ13<0.16.Received 27 January 2012DOI:https://doi.org/10.1103/PhysRevLett.108.131801© 2012 American Physical Society

Neutrino mass hierarchy determination using reactor antineutrinos

Building on earlier studies, we investigate the possibility to determine the type of neutrino mass spectrum (i.e., "the neutrino mass hierarchy") in a high statistics reactor electron antineutrino experiment with a relatively large KamLAND-like detector and an optimal baseline of 60 Km. We analyze systematically the Fourier Sine and Cosine Transforms (FST and FCT) of simulated reactor antineutrino data with reference to their specific mass hierarchy-dependent features discussed earlier in the literature. We perform also a binned \chi^2 analysis of the sensitivity of simulated reactor electron antineutrino event spectrum data to the neutrino mass hierarchy, and determine, in particular, the characteristics of the detector and the experiment (energy resolution, visible energy threshold, exposure, systematic errors, binning of data, etc.), which would allow us to get significant information on, or even determine, the type of the neutrino mass spectrum. We find that if \sin^2 2\theta_{13} is sufficiently large, \sin^2 2\theta_{13} \gtap 0.02, the requirements on the set-up of interest are very challenging, but not impossible to realize.