Search

A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment’s antineutrino detectors is presented in detail. The energy nonlinearity originates from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by γ calibration points from deployed and naturally occurring radioactive sources, the β spectrum from ^(12)B decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV.

The Daya Bay Reactor Neutrino Experiment, located in southeast China, was designed to measure short baseline oscillation of electron antineutrinos originating from six 2.9 GW$_{th}$ nuclear reactors. Since 2011, it has collected an unprecedented sample of millions of reactor antineutrino candidates, the largest sample in the world up to date, which led to the discovery of the non-zero $\theta_{13}$ mixing angle just in 2012. In this talk, we present an overview of the latest results from Daya Bay including the measurement of oscillation parameters driving the reactor antineutrino disappearance at short baseline, with the most precise measurement of the $\theta_{13}$ mixing angle in the world, search for light sterile neutrino mixing, and search for electron antineutrinos associated with gravitational wave events among others.

The Daya Bay Reactor Neutrino Experiment utilizes eight functionally identical detectors with large target volume to measure the antineutrino flux emitted from three pairs of powerful nuclear reactors at different baselines. The detectors are placed underground to provide enough shielding against cosmic rays induced backgrounds. The experiment can perform a high-statistics determination of the absolute reactor antineutrino flux and spectrum. It’s found that a deviation in the measured positron prompt energy spectrum with the comparison to model predictions. It’s observed a local discrepancy in the energy range of 4-6 MeV. The experiment gave the first measurement of individual spectra from 235U and 239Pu. This paper will report the latest measurements of antineutrino flux, spectral shape and evolution of these two quantities with nuclear fuel at Daya Bay.

To better understand the energy response of the Antineutrino Detector (AD), the Daya Bay Reactor Neutrino Experiment installed a full Flash ADC readout system on one AD that allowed for simultaneous data taking with the current readout system. This paper presents the design, data acquisition, and simulation of the Flash ADC system, and focuses on the PMT waveform reconstruction algorithms. For liquid scintillator calorimetry, the most critical requirement to waveform reconstruction is linearity. Several common reconstruction methods were tested but the linearity performance was not satisfactory. A new method based on the deconvolution technique was developed with 1% residual non-linearity, which fulfills the requirement. The performance was validated with both data and Monte Carlo (MC) simulations, and 1% consistency between them has been achieved.

The Daya Bay Reactor Neutrino Experiment was designed to measure θ13, the smallest mixing angle in the three-neutrino mixing framework, with unprecedented precision. The experiment consists of eight functionally identical detectors placed underground at different baselines from three pairs of nuclear reactors in South China. Since Dec. 2011, the experiment has been running stably for more than 4 years, and has collected the largest reactor anti-neutrino sample to date. Daya Bay greatly improved the precision on θ13 and made an independent measurement of the effective mass splitting in the electron antineutrino disappearance channel. Daya Bay also performed a number of other precise measurements, such as a high-statistics determination of the absolute reactor antineutrino flux and spectrum, as well as a search for sterile neutrino mixing, among others. The most recent results from Daya Bay are discussed in this paper, as well as the current status and future prospects of the experiment.

The Daya Bay reactor neutrino experiment has been designed to precisely measure the least known neutrino mixing angle θ 13 . In March 2012, Daya Bay collaboration announced [Daya Bay Collaboration (F. P. An et al.), Observation of electron-antineutrino disappearance at Daya Bay, Phys. Rev. Lett. 108 (2012) 171803] the observation of non-zero value of sin 2 ⁡ 2 θ 13 . Because of large statistics of detected antineutrinos and excellent performance of the experiment, Daya Bay continuously improves the precision of world best measurement of sin 2 ⁡ 2 θ 13 . In addition it provides results on neutrino mass splitting Δ m e e 2 competitive with measurements of other experiments, results on precise measurement of reactor fluxes and on limits of the existence of hypothetical fourth neutrino. In this paper, we report the results available by the time of the 6th Capri workshop: the measurement of oscillation parameters sin 2 ⁡ ( 2 θ 13 ) = 0.084 ± 0.005 and | Δ m e e 2 | = ( 2.42 ± 0.11 ) × 10 − 3 eV 2 [Daya Bay Collaboration (F. P. An et al.), New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay, Phys. Rev. Lett. 115 (2015) no. 11, 111802], searches for sterile neutrinos [Daya Bay Collaboration (F. P. An et al.) Search for a Light Sterile Neutrino at Daya Bay, Phys. Rev. Lett. 113 (2014) 141802] and precise measurement of reactor neutrino flux [Daya Bay Collaboration (F. P. An et al.), Measurement of the Reactor Anti-neutrino Flux and Spectrum at Daya Bay, Phys. Rev. Lett. 116 (2016) no. 6, 061801]. These are based on 621 days of measurement, most of the data has been taken in full detector configuration. More precise results [Daya Bay Collaboration (F. P. An et al.), Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment, arXiv:1610.04802 ] with 1230 days of operation have been presented few weeks later at the Neutrino 2016 conference.

The Daya Bay Reactor Neutrino Experiment consists of eight functionally identical detectors placed underground at different baselines from six 2.9 $\mathrm{GW}_{th}$ reactor cores. Since Dec. 2011, the experiment has collected more than 2.2 million inverse beta decay (IBD) candidates, enabling a precision measurement of the absolute reactor antineutrino flux and spectrum, and their fuel-dependent evolution. The comparison between measured spectrum and predictions from Huber-Mueller model revealed a 2.9 $\sigma$ deviation for the whole energy region and mostly pronounced in the region around 4-6 MeV. The measurement of the evolution of the reactor antineutrino flux and spectrum showed a 2.8 $\sigma$ discrepancy in the antineutrino flux variation with respect to the reactor fuel composition. The discrepancy suggests an overestimation of the predicted contribution from the $\mathrm{^{235}U}$ fission isotope and indicates that this isotope could be primary contributor to the reactor antineutrino anomaly.

The Daya Bay Reactor Neutrino Experiment was designed to determine theta13, the smallest mixing angle in the three-neutrino mixing framework, with unprecedented precision. Daya Bay provided theta13 with the best precision and made an independent measurement of the effective mass splitting in the electron antineutrino disappearance channel [1]. Daya Bay also performed a number of other precise measurements, such as a high-statistics determination of the absolute reactor antineutrino flux and spectrum, and study of their evolution, as well as a search for sterile neutrino mixing, among others. A precision evaluation of the antineutrino energy spectra is a fundament for neutrino oscillation investigation, so an accurate conversion of the detector response to the antineutrino energy is a key attribute of the analysis. This is named as the detector energy response model, which is a subject of the presentation. The model involves the major sources of energy-response non-linearity which originates from processes in the liquid scintillator and readout electronics. They are treated differently for response to electrons, gamma’s and positrons. Also other potential biases related to energy calibration are taken into account.

With the end of Daya Bay experimental operations in December 2020, I review the history, discoveries, measurements and impact of the Daya Bay reactor neutrino experiment in China., Submitted to MPLA

Ling Xin examines the legacy of the recently closed Daya Bay Reactor Neutrino Experiment on neutrino physics, US–China collaborations and future neutrino facilities

We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor $\overline{\nu}_{e}$ inverse beta decay candidates observed over 1958 days of data collection. The installation of a Flash-ADC readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic $^9$Li and $^8$He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative $\overline{\nu}_{e}$ rates and energy spectra among detectors yields $\sin^{2}2\theta_{13} = 0.0856\pm 0.0029$ and $\Delta m^2_{32}=(2.471^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the normal hierarchy, and $\Delta m^2_{32}=-(2.575^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the inverted hierarchy., Comment: 6 pages, 4 figures, and 1 table. v4: the published version

The Daya Bay Reactor Neutrino Experiment consists of eight functionally identical detectors placed underground at different baselines from six $\mathrm{2.9~GW_{th}}$ nuclear reactors. With a growing dataset that constitutes the largest sample of reactor antineutrino interactions ever collected to date, Daya Bay is able to study a wide range of topics of interest in neutrino physics. In this letter I review the latest results from Daya Bay on different fronts, such as the latest measurement of the oscillation parameters that drive the disappearance of electron antineutrinos at short baselines, and a search for light sterile neutrino mixing, among others. I also describe a recent measurement of the evolution of the reactor antineutrino flux and spectrum over multiple fuel cycles in 1230 days. A $3.1\sigma$ discrepancy in the antineutrino flux evolution with recent predictions is observed, indicating an overestimation of the predicted antineutrino flux from $^{235}$U and suggesting that this fission isotope could be the primary contributor to the reactor antineutrino anomaly.

Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay's liquid scintillator is measured to be $Y_n=(10.26\pm 0.86)\times 10^{-5}$, $(10.22\pm 0.87)\times 10^{-5}$, and $(17.03\pm 1.22)\times 10^{-5}~\mu^{-1}~$g$^{-1}~$cm$^2$ at depths of 250, 265, and 860 meters-water-equivalent. These results are compared to other measurements and the simulated neutron yield in Fluka and Geant4. A global fit including the Daya Bay measurements yields a power law coefficient of $0.77 \pm 0.03$ for the dependence of the neutron yield on muon energy., Comment: 13 pages, 13 figures

Recent results from the Daya Bay Reactor Neutrino Experiment are presented. These results include the latest measurements of the mixing parameters θ 13 and | Δ m e e 2 | based on a combined analysis of the detected ν ‾ e rates and energy spectra, an independent measurement of θ 13 using inverse-beta decays associated with n-H captures, a search for light sterile neutrino in the 10 − 3 eV 2 | Δ m 41 2 | 0.3 eV 2 range, and a measurement of the absolute antineutrino flux. Future prospects of the Daya Bay Reactor Neutrino Experiment are also discussed.

We describe the design, installation, and operation of a purification system that is able to provide large volumes of high purity ASTM (D1193-91) Type-I water to a high energy physics experiment. The water environment is underground in a lightly sealed system, and this provides significant challenges to maintaining high purity in the storage pools, each of which contains several thousand cubic meters. High purity is dictated by the need for large optical absorption length, which is critical for the operation of the experiment. The system is largely successful, and the water clarity criteria are met. We also include a discussion of lessons learned., Comment: Keywords: High purity water, Deionization

We analyzed the evolution data of the Daya Bay reactor neutrino experiment in terms of short-baseline active-sterile neutrino oscillations taking into account the theoretical uncertainties of the reactor antineutrino fluxes. We found that oscillations are disfavored at $2.6\sigma$ with respect to a suppression of the $^{235}\text{U}$ reactor antineutrino flux and at $2.5\sigma$ with respect to variations of the $^{235}\text{U}$ and $^{239}\text{Pu}$ fluxes. On the other hand, the analysis of the rates of the short-baseline reactor neutrino experiments favor active-sterile neutrino oscillations and disfavor the suppression of the $^{235}\text{U}$ flux at $3.1\sigma$ and variations of the $^{235}\text{U}$ and $^{239}\text{Pu}$ fluxes at $2.8\sigma$. We also found that both the Daya Bay evolution data and the global rate data are well-fitted with composite hypotheses including variations of the $^{235}\text{U}$ or $^{239}\text{Pu}$ fluxes in addition to active-sterile neutrino oscillations. A combined analysis of the Daya Bay evolution data and the global rate data shows a slight preference for oscillations with respect to variations of the $^{235}\text{U}$ and $^{239}\text{Pu}$ fluxes. However, the best fits of the combined data are given by the composite models, with a preference for the model with an enhancement of the $^{239}\text{Pu}$ flux and relatively large oscillations., Comment: 9 pages

Neutrinos are elementary particles in the standard model of particle physics. There are 3 flavors of neutrinos that oscillate among themselves and their oscillation can be described by a 3×3 unitary matrix, containing three mixing angles θ12, θ23, θ13, and one CP phase. Both θ12 and θ23 are known from previous experiments. The Daya Bay experiment gave the first definitive non-zero value in 2012. Daya Bay use the 1230 days data to obtain the most precise measurement of sin22θ13 =0.08421±0.0027(stat.)±0.0019(syst.) and = (math) × 10−3eV2. Experiment has measured the flux and spectrum of the reactor antineutrino. Flux is consistent with previous short baseline experiments and spectrum different from prediction with significance 4.4σ in 4-6 MeV energy region. Experiment also measure the IBD yield per fission from individual isotopes (235U, 239Pu, 238U, 241Pu) and found that IBD yield of 235U is 7.8% lower than prediction. For light sterile neutrino serach, there are no hint of light sterile neutrino observed from Daya Bay data and give the most stringent limit for (math) 2.

We report on the production and characterization of liquid scintillators for the detection of electron antineutrinos by the Daya Bay Reactor Neutrino Experiment. One hundred eighty-five tons of gadolinium-loaded (0.1% by mass) liquid scintillator (Gd-LS) and two hundred tons of unloaded liquid scintillator (LS) were successfully produced from a linear-alkylbenzene (LAB) solvent in six months. The scintillator properties, the production and purification systems, and the quality assurance and control (QA/QC) procedures are described., Comment: 15 pages, 11 figures. Submitted to Nuclear Instruments and Methods in Physics Research Section A

The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle θ 13 with a significance of 7.7 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected by six 20-ton target-mass detectors of identical design, deployed in two near and one far underground experimental halls. With a 116.8 kton-GWth-day live-time exposure in 139 days, 28,909 and 205,308 electron-antineutrino candidates were detected at the far hall and near halls respectively. The ratio of the observed to expected number of antineutrinos at the far hall is R = 0.944 ± 0.007 ( stat ) ± 0.003 ( syst ) . A rate-only analysis finds sin 2 2 θ 13 = 0.089 ± 0.010 ( stat ) ± 0.005 ( syst ) in a three-neutrino framework. The experiments will continue for several years and a more precise neutrino mixing angle θ 13 will be given in the future.

The Daya Bay Reactor Neutrino Experiment was designed to achieve a sensitivity on the value of sin^2 2θ_(13) to better than 0.01 at 90% CL. The experiment consists of eight antineutrino detectors installed underground at different baselines from six nuclear reactors. With data collected with six antineutrino detectors for 55 days, Daya Bay announced the discovery of a non-zero value for sin^2 2θ_(13) with a significance of 5.2 standard deviations in March 2012. The most recent analysis with 139 days of data acquired in a six-detector configuration yields sin^2 2θ_(13) = 0.089 ± 0.010 (stat.) ± 0.005 (syst.), which is the most precise measurement of sin^2 2θ_(13) to date.

The Daya Bay Reactor Neutrino Experiment is to measure the smallest mixing angle θ13.The experiment contains three major experiment halls,Daya Bay near site,Linao near site and far site,and two major kinds of detectors,antineutrino detector which is to detect the antineutrinos by the inverse beta-de...

Neutrinos are elementary particles in the Standard Model. Neutrino oscillation is a quantum mechanical phenomenon beyond the Standard Model. Neutrino oscillation can be described by two independent mass-squared differences Delta m (21) (2) , Delta m (31) (2) (or Delta m (32) (2) ) and a 3 x 3 unitary matrix, containing three mixing angles theta (12), theta (23), theta (13), and one charge-parity (CP) phase. theta (12) is about 34A degrees and determined by solar neutrino experiments and the reactor neutrino experiment KamLAND. theta (23) is about 45A degrees and determined by atmospheric neutrino experiments and accelerator neutrino experiments. theta (13) can be measured by either accelerator or reactor neutrino experiments. On Mar. 8, 2012, the Daya Bay Reactor Neutrino Experiment reported the first observation of non-zero theta (13) with 5.2 standard deviations. In June, with 2.5x previous data, Daya Bay improved the measurement of sin(2)2 theta (13) = 0.089 +/- 0.010(stat) +/- 0.005(syst).

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{\mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946\pm0.020$ ($0.992\pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$\sigma$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$\sigma$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions., Comment: version published in Chinese Physics C

A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW$_{\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overline{\nu}_{e}$'s. Comparison of the $\overline{\nu}_{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim$1500-1950 m) relative to detectors near the reactors ($\sim$350-600 m) allowed a precise measurement of $\overline{\nu}_{e}$ disappearance. More than 2.5 million $\overline{\nu}_{e}$ inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (Dec. 2011--Jul. 2012) with a subsequent 1013 days using the complete configuration of eight detectors (Oct. 2012--Jul. 2015). The $\overline{\nu}_{e}$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$. The energy dependence of $\overline{\nu}_{e}$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle $\sin^22\theta_{13}=0.0841 \pm 0.0027(\mathrm{stat.}) \pm 0.0019(\mathrm{syst.})$ and the effective neutrino mass-squared difference of $\left|{\Delta}m^2_{\mathrm{ee}}\right|=(2.50 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$. Analysis using the exact three-flavor probability found ${\Delta}m^2_{32}=(2.45 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ assuming the normal neutrino mass hierarchy and ${\Delta}m^2_{32}=(-2.56 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ for the inverted hierarchy., Comment: 44 pages, 44 figures

The Daya Bay reactor experiment has reported the most precise measurement of sin$^{2}2\theta_{13}$ and $\Delta m^{2}_{ee}$ by using a data set with the fully constructed design of 8 antineutrino detectors (ADs). We also report on a new independent measurement of sin$^{2}2\theta_{13}$ from neutron capture on hydrogen, which confirms the results using gadolinium caputres. Several other analyses are also performed, including a measurements on the absolute reactor antineutrino flux and a search for light sterile neutrinos. Prospects for new analyses such as searching for CPT/LI violation at Daya Bay are ongoing., Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016

This article reports an improved independent measurement of neutrino mixing angle θ_(13) at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse β-decays with the emitted neutron captured by hydrogen, yielding a data set with principally distinct uncertainties from that with neutrons captured by gadolinium. With the final two of eight antineutrino detectors installed, this study used 621 days of data including the previously reported 217-day data set with six detectors. The dominant statistical uncertainty was reduced by 49%. Intensive studies of the cosmogenic muon-induced ^9Li and fast neutron backgrounds and the neutron-capture energy selection efficiency, resulted in a reduction of the systematic uncertainty by 26%. The deficit in the detected number of antineutrinos at the far detectors relative to the expected number based on the near detectors yielded sin^22θ_(13) =0.071±0.011in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.

The Daya Bay reactor neutrino experiment is designed to precisely measure the neutrino mixing angle theta(13). The anti-neutrino detectors are shielded by highly purified water against radioactivity and spallation neutrons from surrounding rocks. The water also serves as a Cherenkov detector to tag cosmic-ray muons, which induce main backgrounds. In order to study water purification and details of the detector response, a prototype water Cherenkov detector is constructed at the Institute of High Energy Physics (IHEP), Beijing. The detector is divided by Tyvek into two sections and viewed by two 8 in. photomultipliers. Cosmic-ray muons are used for detector response studies and a Monte Carlo simulation based on the Geant4 package shows good agreement with the experimental data. (C) 2012 Elsevier B.V. All rights reserved.

The Daya Bay reactor neutrino experiment is aimed at a measurement of the neutrino mixing angle θ 13 with a sensitivity of 0.01 in sin 2 2 θ 13 at the 90% confidence level. The experiment design takes two short baselines and one long baseline positioned with identical detectors to measure the relative rates and energy spectra of electron antineutrinos. Civil and detector construction is ongoing. Data taking will begin in Autumn 2012 and last for three years.

Weathered troughs are frequently encountered in granites. They can cause problems to tunneling in the rocks and have to be properly addressed. The structures or spatial shapes of weathered troughs were seldom clarified in the past. In this paper, four weathered troughs are identified by means of geophysical exploration, core drilling, logging, and in-situ stress measurement at Daya Bay reactor-neutrino experiment site in Shenzhen, China. The weathered troughs are exposed on the ground or partially covered by grass and soils, which will threaten the safety of horizontal tunneling at a shallow depth. High electrical resistivity (HER) method is adopted for its feasibility and practicality, in combination with field geological observation, ultrasonic televiewer in boreholes and in-situ stress measurement. By comparing the HER values of completely decomposed to fresh rocks, it is indicated that the HER values of weathered troughs in natural state are 0.4–100 Ω · m, and the in-situ stress is abnormally lower than those at upper and lower layers. Field investigations show that the depths of the four weathered troughs are 30–182 m, with bottom elevation over 10 m. The volume of each weathered trough is mostly over 1 × 106 m3 in inverted conic form. The weathered troughs often occur in various kinds of landforms, such as ridges, gullies or gently dipping dish-like depression areas. Faults and boundaries of different granitic plutons as well as joints govern the formation, locations and strikes of these troughs under development.

Resistive plate chambers will be used in the Daya Bay reactor neutrino experiment to help veto backgrounds created by cosmic-ray muons. The mass production of RPCs began in 2008 and by the end of 2009, 1600 RPCs (3500 m2) had been produced and tested. This paper describes the production and quality control procedures, and quality assurance using cosmic-ray testing.

Resistive Plate Chamber (RPC) modules will be used as one part of the cosmic muon veto system in the Daya Bay reactor neutrino experiment. A total of 189 RPC modules will cover the three water pools in the experiment. To achieve track reconstruction and high efficiency, each module consists of 4 layers, each of which contains two sizes of bare chambers. The placement of bare chambers is reversed in different layers to reduce the overlapping dead areas. The module efficiency and patch efficiency were studied both in simulation and test of the data analysis. 143 modules have been constructed and tested. The preliminary study shows that the module and patch 3 out of 4 layers efficiency reaches about 98%.

The Daya Bay Reactor Neutrino Experiment consists of seventeen detectors distributed in three underground experimental halls. Each detector has a separate VME readout crate that contains the trigger and electronics modules. The data acquisition (DAQ) system reads data fragments from electronics and trigger modules and concatenates them into an event in each crate. The DAQ monitors the data quality, merges the event streams from each hall, and records these data to disk. The DAQ architecture is designed as a multi-level system based on the BESIII DAQ and ATLAS TDAQ systems using embedded Linux, VME bus system, advanced commercial computers and distributed network technologies. This paper presents the main DAQ design requirements, and the hardware and software architectures.

We have designed a local trigger board for the Daya Bay reactor neutrino experiment, which is aimed to measure the neutrino mixing angle sin(2) 2 theta(13) with a precision down to 1% level. The local trigger board processes both the total number of coincident photomultiplier tube (PMT) hits and the PMT energy sum to make trigger decisions. With this design, a high trigger probability is achieved to meet the system requirement. The design of the local trigger board is presented. (C) 2011 Elsevier B.V. All rights reserved.

The Daya Bay reactor neutrino experiment is designed to precisely determine the neutrino mixing angle theta(13). An innovative design of the Daya Bay antineutrino detector will use optical reflective panels at the top and the bottom of the detector cylinder. This design has been tested using a prototype detector constructed at the Institute of High Energy Physics (IHEP), Beijing. A maximum likelihood event reconstruction method has been developed and tested for such a reflective prototype detector. (C) 2010 Elsevier B.V. All rights reserved.

The Daya Bay reactor neutrino experiment is designed to precisely measure the neutrino mixing angle θ13. In order to study the details of the detector response and finalize the detector design, a prototype neutrino detector with a scale of 1/3 in diameter is constructed at the Institute of High Energy Physics (IHEP), Beijing. The detector is viewed by 45 8″ photomultipliers, which are calibrated by LED light pulse. The energy response of the detector, including the resolution, linearity, spatial uniformity, etc., is studied by radioactive sources 133Ba, 137Cs, 60Co, and 22Na at various locations of the detector. The measurement shows that the detector, particularly the specially designed optical reflectors, works as expected. A Monte Carlo simulation based on the Geant4 package shows a good agreement with the experimental data.

Author(s): Chu, MC; Kwan, KK; Kwok, MW; Kwok, T; Leung, JKC; Leung, KY; Lin, YC; Luk, KB; Pun, CSJ | Abstract: We developed a highly sensitive, reliable and portable automatic system (H3) to monitor the radon concentration of the underground experimental halls of the Daya Bay Reactor Neutrino Experiment. H3 is able to measure radon concentration with a statistical error less than 10% in a 1-h measurement of dehumidified air (R.H. 5% at 25°C) with radon concentration as low as 50 Bq/m3. This is achieved by using a large radon progeny collection chamber, semiconductor α-particle detector with high energy resolution, improved electronics and software. The integrated radon monitoring system is highly customizable to operate in different run modes at scheduled times and can be controlled remotely to sample radon in ambient air or in water from the water pools where the antineutrino detectors are being housed. The radon monitoring system has been running in the three experimental halls of the Daya Bay Reactor Neutrino Experiment since November 2013.

This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the $2\times10^{-4} \lesssim |\Delta m^{2}_{41}| \lesssim 0.3$ eV$^{2}$ mass range. The resulting limits on $\sin^{2}2\theta_{14}$ are improved by approximately a factor of 2 over previous results and constitute the most stringent constraints to date in the $|\Delta m^{2}_{41}| \lesssim 0.2$ eV$^{2}$ region., Comment: 6 pages, 3 figures, 1 table

We present an evaluation of the background induced by $^{241}$Am-$^{13}$C neutron calibration sources in the Daya Bay reactor neutrino experiment. As a significant background for electron-antineutrino detection at 0.26$\pm$0.12 per detector per day on average, it has been estimated by a Monte Carlo simulation that was benchmarked by a special calibration data set. This dedicated data set also provided the energy spectrum of the background., 15 pages, 7 figures

The Daya Bay Reactor Neutrino Experiment collected ∼300,000 inverse beta decay events in three antineutrino detectors at two sites near the reactor cores, over 217 days. This paper will present the methods we use to convert the observed positron energy spectrum to a reactor antineutrino spectrum, with an universal unit cm2/ f ission/MeV . We also present our results for the absolute reactor antineutrino flux and spectrum. Comparisons are made with the predictions of various flux models, an example of using our spectrum to predict the spectrum from other reactor experiments will also be described.

In the Daya Bay Reactor Neutrino Experiment 960 20-cm-diameter waterproof photomultiplier tubes are used to instrument three water pools as Cherenkov detectors for detecting cosmic-ray muons. Of these 960 photomultiplier tubes, 341 are recycled from the MACRO experiment. A systematic program was undertaken to refurbish them as waterproof assemblies. In the context of passing the water leakage check, a success rate better than 97% was achieved. Details of the design, fabrication, testing, operation, and performance of these waterproofed photomultiplier-tube assemblies are presented., Comment: 16 pages, 11 figures. Submitted to Nucl. Instr. Meth

We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9$\times$10$^5$ GW$_{\rm th}$-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six $^{241}$Am-$^{13}$C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of $\sin^{2}2\theta_{13}$ and $|\Delta m^2_{ee}|$ were halved as a result of these improvements. Analysis of the relative antineutrino rates and energy spectra between detectors gave $\sin^{2}2\theta_{13} = 0.084\pm0.005$ and $|\Delta m^{2}_{ee}|= (2.42\pm0.11) \times 10^{-3}$ eV$^2$ in the three-neutrino framework., Comment: Updated to match final published version

Recent measurements of neutrino fluxes inside the Daya Bay Reactor Neutrino Experiment, pictured here, seemed to turn up significantly fewer neutrinos than theorists had predicted, potentially due to the existence of sterile neutrinos. Image courtesy of Interactions.org/Institute of High Energy Physics, Chinese Academy of Sciences.

The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle θ13 with a significance of 7.7 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected in six antineutrino detectors deployed in two near and one far underground experimental halls. With a 116.8 kton-GWth-day live-time exposure in 139 days, 28,909 (205,308) electron-antineutrino candidates were detected at the far hall (near hall). The ratio of the observed to expected number of antineutrinos at the far hall is R = 0.944 ± 0.007 ± 0.003 (syst). A rate-only analysis finds sin22θ13 = 0.089 ± 0.010 (stat) ± 0.005 (syst) in a three-neutrino framework.

The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation, and as water Cherenkov detectors that efficiently detect cosmic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. Design, construction, operation, and performance of these muon detectors are described., Comment: 13 pages, 22 figures, to appear as NIM-A 773 (2015) 8-20

The Daya Bay reactor neutrino experiment has observed the disappearance of electron antineutrinos from nuclear reactors at ∼kilometer baselines. The relative measurement of the ν¯e rate and spectrum between near and far detectors allows for a precision measurement of the oscillation parameters sin2 2θ13 and |Δmee2|. Two new antineutrino detectors (ADs) were installed in summer 2012, bringing the experiment to the final 8-AD configuration. With 621 days of data, Daya Bay has measured sin2 2θ13 = 0.084 ± 0.005 and |Δmee2|=2.44−0.11+0.10×10−3 eV2. This is the most precise measurement of sin2 2θ13 to date and the most precise measurement of |Δmee2| in this channel. Several other analyses are also performed, including an independent measurement of sin2 2θ13 using ν¯e samples tagged by neutron capture on hydrogen, a search for light sterile neutrinos, and a measurement of the absolute reactor antineutrino flux.

This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9~GW$_{th}$ nuclear reactors with six detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1,579~m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296,721 and 41,589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 $\pm$ 0.04) $\times$ 10$^{-18}$~cm$^2$/GW/day or (5.92 $\pm$ 0.14) $\times$ 10$^{-43}$~cm$^2$/fission. This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is $0.946\pm0.022$ ($0.991\pm0.023$) relative to the flux predicted with the Huber+Mueller (ILL+Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2$\sigma$ over the full energy range with a local significance of up to $\sim$4$\sigma$ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.