Reactor Neutrino Oscillation Experiments Research Articles

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.

Slow control systems of the Reactor Experiment for Neutrino Oscillation

The RENO experiment has been in operation since August 2011 to measure reactor antineutrino disappearance using identical near and far detectors. For accurate measurements of neutrino mixing parameters and efficient data taking, it is crucial to monitor and control the detector in real time. Environmental conditions also need to be monitored for stable operation of detectors as well as for safety reasons. In this paper, we report the design, hardware, operation, and performance of the slow control system.

Reactor Experiment for Neutrino Oscillation in Korea

Reactor Experiment for Neutrino Oscillation in Korea

Constraint on neutrino decay with medium-baseline reactor neutrino oscillation experiments

The experimental bound on lifetime of ν 3, the neutrino mass eigenstate with the smallest ν e component, is much weaker than those of ν 1 and ν 2 by many orders of magnitude to which the astrophysical constraints apply. We argue that the future reactor neutrino oscillation experiments with medium-baseline (∼50 km), such as JUNO or RENO-50, has the best chance of placing the most stringent constraint on ν3 lifetime among all neutrino experiments which utilize the artificial source neutrinos. Assuming decay into invisible states, we show by a detailed χ 2 analysis that the ν 3 lifetime divided by its mass, τ 3 /m 3, can be constrained to be τ 3 /m 3 > 7.5 (5.5) × 10−11 s/eV at 95% (99%) C.L. by 100 kt·years exposure by JUNO. It may be further improved to the level comparable to the atmospheric neutrino bound by its longer run. We also discuss to what extent ν 3 decay affects mass-ordering determination and precision measurements of the mixing parameters.

New results from RENO and prospects with RENO-50

RENO (Reactor Experiment for Neutrino Oscillation) has made a definitive measurement of the smallest mixing angle θ13 in 2012, based on the disappearance of electron antineutrinos. More precise measurements have been obtained and presented on the mixing angle and the reactor neutrino spectrum, using ∼800 days of data. We have observed an excess of inverse-beta-decay (IBD) prompt spectrum near 5 MeV with respect to the most commonly used models. The excess is found to be consistent with coming from reactors. We have also successfully measured the reactor neutrino flux with a delayed signal of neutron capture on hydrogen. A future reactor neutrino experiment of RENO-50 is proposed to determine the neutrino mass hierarchy and to make highly precise measurements of θ12, Δm212, and Δm312. Physics goals and sensitivities of RENO-50 are presented with a strategy of obtaining an extremely good energy resolution toward the neutrino mass hierarchy.

Study on the Neutrino Oscillation with a Next Generation Medium-Baseline Reactor Experiment

For over fifty years, reactor experiments have played an important role in neutrino physics, in both discoveries and precision measurements. One of the methods to verify the existence of neutrino is the observation of neutrino oscillation phenomena. Electron antineutrinos emitted from a reactor provide the measurement of the small mixing angleθ13, providing rich programs of neutrino properties, detector development, nuclear monitoring, and application. Using reactor neutrinos, future reactor neutrino experiments, more precise measurements ofθ12, Δm122, and mass hierarchy will be explored. The precise measurement ofθ13would be crucial for measuring the CP violation parameters at accelerators. Therefore, reactor neutrino physics will assist in the complete understanding of the fundamental nature and implications of neutrino masses and mixing. In this paper, we investigated several characteristics of RENO-50, which is a future medium-baseline reactor neutrino oscillation experiment, by using the GloBES simulation package.

Dissipation and θ 13 in neutrino oscillations

We obtain a complete survival and transition probability involving three neutrino flavors when dissipation effects in vacuum are taken into consideration. In an approach that presents decoherence and relaxation effects, we study the behavior of the probabilities obtained from complete positivity constraints. Making the von Neumann entropy increase in time, many cases can be obtained and studied with the Lindblad master equation with addition of only one or two parameters related to dissipation. New possibilities are obtained when we take into account two decoherence parameters with different magnitudes which are given by reactor and accelerator neutrino oscillation experiments. We also present a model with only one parameter that has an important symmetry property, which can be used when the effective matter potential is important. Furthermore, the dissipation effects can contribute to the appearance of neutrinos that can hide or imitate the θ13 effects and we study these possibilities showing that dissipative effects have an important role in three-neutrino oscillations.

Observation of Reactor Antineutrino Disappearance at RENO and Future Plan

Reactor Experiment for Neutrino Oscillation (RENO) in South Korea observed electron anti-neutrino disappearance using data taken from August 2011 to March 2012 (about 222 live-days) at Yonggwang nuclear reactor site. The observed deficit resulted in measuring the last unknown neutrino mixing angle, sin22θ13, as 0.113 +/- 0.013 (stat) +/- 0.019 (sys.) which is 4.9 sigma level discovery over no oscillation hypothesis. We have taken about 440 live-days of data in total so far and those data are being analyzed. The ultimate goal of RENO analysis is that we would like to reduce statistical and systematic errors down to more than half of what are now by taking data for 3 years in total and by improving analysis method and reducing background. At the end, our future project, RENO-50, is discussed.

Observation of Reactor Electron Antineutrino Disappearance at RENO

The Reactor Experiment for Neutrino Oscillation (RENO) has obtained a definitive measurement of the smallest neutrino mixing angle of θ13 by observing the disappearance of electron antineutrinos emitted from a nuclear reactor, excluding the no-oscillation hypothesis at 4.9 σ. From the deficit, the best fit value of sin22θ13 is obtained as 0.113±0.013(stat.)±0.019(syst.) based on a rate-only analysis. Antineutrinos from six 2.8 GWth reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors at 294 m and 1383 m, respectively, from the reactor array center. In the 229 day 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 the reactor antineutrinos in the far detector is 0.920±0.009(stat.)±0.014(syst.).

Relatively large Theta13 from modification to the tri-bimaximal, bimaximal and democratic neutrino mixing matrices

Inspired by the indication of a relatively large θ 13 from accelerator and reactor neutrino oscillation experiments, we provide a systematic study of general modifications to the three well-studied neutrino mixing patterns, i.e., tri-bimaximal, bimaximal and democratic lepton mixing matrices. The correlation between θ 13 and the other two neutrino mixing angles are derived for each types of additional rotations. Predictions on θ 12 and θ 23 are also studied. Our study shows that, although some types of additional rotations are already excluded by the current global fit data of neutrino mixing angles, several types of additional rotations still survive. Our results may provide a guideline for the model building in neutrino physics.

Production and optical properties of Gd-loaded liquid scintillator for the RENO neutrino detector

Reactor experiment for neutrino oscillation (RENO) began data-taking from August 2011. It successfully observed reactor antineutrino disappearance in April 2012 to measure the smallest mixing angle of θ13. Two identical detectors, one at near location and the other at far location, are constructed at the Yonggwang nuclear power plant in South Korea, to compare the observed reactor neutrino fluxes. Each RENO detector is filled with 16 mass tons of Gadolinium loaded liquid scintillator (GdLS) in the neutrino target region, and with 28 mass tons of unloaded liquid scintillator (LS) in the γ-catcher region surrounding the target. LS was developed to satisfy chemical, physical, optical properties, and safety requirements. Linear alkyl benzene (LAB) was chosen as a solvent because of its high flash-point, sufficient light yield, and being environmentally friendly. GdLS is carefully developed to keep a long attenuation length and high light yield for a long time period. In this paper, we report the characteristics and mass production of the RENO LS and GdLS.

Status of the RENO Reactor Neutrino Experiment

The Reactor Experiment for Neutrino Oscillation (RENO) is a reactor based neutrino oscillation experiment to measure the neutrino mixing angle θ13 using anti-neutrinos emitted from the Yonggwang nuclear power plant in Korea. Its thermal power output is 16.4 Gwth. The experimental setup consists of two identical 16-ton gadolinium-loaded liquid scintillator detectors. The near and far detectors are placed roughly 290 m and 1.4 km from the center of the reactor array, respectively. The near detector is constructed at underground of a 70 m high hill and the far detector at underground of a 260 m high mountain. The construction of experimental halls and access tunnels for both near and far detector sites was completed in early 2009. The experiment is planned to start data-taking from early 2011. An expected number of observed anti-neutrinos is roughly 1300 per day and 100 per day in the far and near detector, respectively. We expect that an estimated systematic uncertainty is less than 0.5%. With three years of data taken, RENO is sensitive to measure sin2(2θ13)>0.02. Sensitivity is ten times better than the current limit obtained by Chooz. In this review, current status of RENO is presented.

Construction and properties of acrylic vessels in the RENO detector

The aim of the RENO (Reactor Experiment for Neutrino Oscillation) is to measure the smallest neutrino mixing angle, θ13. The RENO detector consists of four concentric cylindrical layers: the target, γ-catcher, buffer and veto. Acrylic is used for the target and γ-catcher vessels, both of which contain liquid scintillator. Acrylic was chosen because it has good transmittance in the wavelength range of 400–430nm and also does not react with liquid-scintillating solvents. In order to reduce systematic uncertainties, the target volume should be identical to a level of less than 0.1% between the near and far detectors. Furthermore, the acrylic vessel should not have any leaks. In this paper, we investigate the optical properties, design and construction of the acrylic vessels used in the RENO detector.

REVIEW OF REACTOR NEUTRINO OSCILLATION EXPERIMENTS

In this document we will review the current status of reactor neutrino oscillation experiments and present their physics potentials for measuring the θ13 neutrino mixing angle. The neutrino mixing angle θ13 is currently a high-priority topic in the field of neutrino physics. There are currently three different reactor neutrino experiments, DOUBLE CHOOZ, DAYA BAY and RENO and a few accelerator neutrino experiments searching for neutrino oscillations induced by this angle. A description of the reactor experiments searching for a nonzero value of θ13 is given, along with a discussion of the sensitivities that these experiments can reach in the near future.

Online Monitor Framework for Network Distributed Data Acquisition Systems

Data acquisition (DAQ) systems for recent high energy physics experiments consist of lots of subsystems distributed in the local area network. Therefore, scalability for the number of connections from subsystems and availability of access via the Internet are required. “Online monitor framework” is a general software framework for online data monitoring, which provides a way to collect monitoring information distributed in the network and pass them though the firewalls. The framework consists of two subsystems; “Monitor Sever” and “Monitor Viewer”. Monitor Server is a core system of the framework. The server collects monitoring information from the DAQ subsystems to provide them to Monitor Viewer. Monitor Viewer is a graphical user interface of the monitor framework, which displays plots in itself. We adapted two types of technologies; Java and HTML5 with Google Web Toolkit, which are independent of operating systems or plugin-libraries like ROOT and contain some functionalities of communicating via the Internet and drawing graphics. The monitoring framework was developed for the Double Chooz reactor neutrino oscillation experiment but is general enough for other experiments. This document reports the structure of the online monitor framework with some examples from the adaption to the Double Chooz experiment.

Online Data Monitoring Framework Based on Histogram Packaging in Network Distributed Data Acquisition Systems

"Online monitor framework" is a new general software framework for online data monitoring, which provides a way to collect information from online systems, including data acquisition, and displays them to shifters far from experimental sites. "Monitor Server", a core system in this framework gathers the monitoring information from the online subsystems and the information is handled as collections of histograms named "Histogram Package". Monitor Server broadcasts the histogram packages to "Monitor Viewers", graphical user interfaces in the framework. We developed two types of the viewers with different technologies: Java and web browser. We adapted XML based file for the configuration of GUI components on the windows and graphical objects on the canvases. Monitor Viewer creates its GUIs automatically with the configuration files.This monitoring framework has been developed for the Double Chooz reactor neutrino oscillation experiment in France, but can be extended for general application to be used in other experiments. This document reports the structure of the online monitor framework with some examples from the adaption to the Double Chooz experiment.

Status of RENO Experiment

An experiment, RENO (Reactor Experiment for Neutrino Oscillation), is under construction to measure the smallest and unknown neutrino mixing angle ( θ 13 ) using anti-neutrinos emitted from the Yonggwang nuclear power plant in Korea. The experimental setup consists of two identical 16-ton Gadolinium loaded liquid scintillator detectors located near and far from the reactor array to measure the deviations from the inverse square distance law. The experiment is planned to start data-taking in early 2011. An estimated systematic uncertainty associated with the measurement is less than 0.6%. Based on three years of data, it would be sensitive to measure the neutrino mixing angle in the range of s i n 2 ( 2 θ 13 ) > 0.02 . In this talk, the status of RENO experiment is described.

Future neutrino long baseline experiments

Very soon a new generation of reactor and accelerator neutrino oscillation experiments—Double Chooz, Daya Bay, Reno and T2K—will seek for oscillation signals generated by the mixing parameter θ13. The knowledge of this angle is a fundamental milestone to optimize further experiments aimed at detecting CP violation in the neutrino sector. Leptonic CP violation is a key phenomenon that has profound implications in particle physics and cosmology but it is clearly out of reach for the aforementioned experiments. Since late 90’s, a worldwide activity is in progress to design facilities that can access CP violation in neutrino oscillation and perform high precision measurements of the lepton counterpart of the Cabibbo-Kobayashi-Maskawa matrix.

Measurement of the refractive index of the LAB-based liquid scintillator and acrylic at RENO

In this paper, we describe the first measurement of the refractive index of the linear alkyl benzene (LAB)-based liquid scintillator and acrylic used at the Reactor Experiment for Neutrino Oscillation (RENO). The refractive index of a material is an important optical property and the prism spectrometer is the most common device for measuring the refractive index. Using the minimum deviation technique, which requires an exact measurement of the apex angle, we determined the refractive indices at six different wavelengths and then fitted them. We also compared the refractive index of the LAB-based liquid scintillator with the refractive indices of other liquid scintillator solvents commonly used in reactor neutrino experiments.

RENO for neutrino mixing angle [formula omitted

The RENO (Reactor Experiment for Neutrino Oscillation) experiment is under construction to measure the value of the smallest and unknown neutrino mixing angle θ 13 . 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. The detectors are near completion, and data-taking is expected to start in mid 2010. The estimated systematic uncertainty associated with the measurement is less than 0.6%, and the expected statistical error is about 0.3%. With three years of data, the experiment will search for mixing angle values of sin 2 2 θ 13 down to 0.02 in the 90% C.L. limit. In this review, the construction status is presented.