Browsing by Author "Kwan, K. K."

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A side-by-side comparison of Daya Bay antineutrino detectors
(1970-01-01)
An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
"The Daya Bay Reactor Neutrino Experiment is designed to determine precisely the neutrino mixing angle theta(13) with a sensitivity better than 0.01 in the parameter sin(2) 2 theta(13) at the 90% confidence level. To achieve this goal, the collaboration will build eight functionally identical antineutrino detectors. The first two detectors have been constructed, installed and commissioned in Experimental Hall 1, with steady data-taking beginning September 23, 2011. A comparison of the data collected over the subsequent three months indicates that the detectors are functionally identical, and that detector-related systematic uncertainties are smaller than requirements. (C) 2012 Elsevier B.V. All rights reserved."
An apparatus for studying spallation neutrons in the Aberdeen Tunnel laboratory
(2013-09-21)
Blyth, S. C.
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Chan, Y. L.
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Chen, X. C.
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Ch, M. C.
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Hahn, R. L.
In this paper, we describe the design, construction and performance of an apparatus installed in the Aberdeen Tunnel laboratory in Hong Kong for studying spallation neutrons induced by cosmic-ray muons under a vertical rock overburden of 611 m water equivalent (m.w.e.). The apparatus comprises six horizontal layers of plastic-scintillator hodoscopes for determining the direction and position of the incident cosmic-ray muons. Sandwiched between the hodoscope planes is a neutron detector filled with 650 kg of liquid scintillator doped with about 0.06% of Gadolinium by weight for improving the efficiency of detecting the spallation neutrons. Performance of the apparatus is also presented. (C) 2013 Elsevier B.V. All rights reserved.
Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay
(2017-06-19)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW(th) reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective Pu-239 fission fractions F-239 from 0.25 to 0.35, Daya Bay measures an average IBD yield (sigma) over bar (f) of (5.90 +/- 0.13) x 10(-43) cm(2)/fission and a fuel-dependent variation in the IBD yield, d sigma(f)/dF(239), of (-1.86 +/- 0.18) x 10(-43) cm(2)/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the Pu-239 fission fraction at 10 standard deviations. The variation in IBD yield is found to be energy dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1 sigma. This discrepancy indicates that an overall deficit in the measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes U-235, Pu-239, U-238, and Pu-241. Based on measured IBD yield variations, yields of (6.17 +/- 0.17) and (4.27 +/- 0.26) x 10(-43) cm(2)/fission have been determined for the two dominant fission parent isotopes U-235 and Pu-239. A 7.8% discrepancy between the observed and predicted U-235 yields suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.
Improved measurement of electron antineutrino disappearance at Daya Bay
(2013-01-01)
An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
We report an improved measurement of the neutrino mixing angle theta(13) from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for sin(2)2 theta(13) with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GW(th) were detected in six antineutrino detectors deployed in two near (flux-weighted baselines of 470 m and 576 m) and one far (1648 m) underground experimental halls. Using 139 days of data, 28909 (205308) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is 0.944 +/- 0.007(stat.)+/- 0.003(syst.). An analysis of the relative rates in six detectors finds sin(2)2 theta(13)= 0.089 +/- 0.010(stat.)+/- 0.005(syst.) in a three-neutrino framework.
Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay
(2017-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
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(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 +/- 0.020 (0.992 +/- 0.021) 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.
Improved measurement of the reactor antineutrino flux and spectrum at Daya Bay
(2017-01-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
;
Bishai, M.
;
Blyth, S.
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(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 +/- 0.020 (0.992 +/- 0.021) 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.
Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment
(2016-10-07)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
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 x 10(-4) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.3 eV(2) mass range. The resulting limits on sin(2) 2 theta(14) are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the vertical bar Delta m(41)(2)vertical bar less than or similar to 0.2 eV(2) region.
Independent measurement of the neutrino mixing angle theta(13) via neutron capture on hydrogen at Daya Bay
(2014-10-03)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A new measurement of the theta(13) mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of the theta(13) measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deficit observed at the far hall is interpreted as sin(2)2 theta(13) = 0.083 +/- 0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin(2)2 theta(13) = 0.089 +/- 0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
Limits on Active to Sterile Neutrino Oscillations from Disappearance Searches in the MINOS, Daya Bay, and Bugey-3 Experiments
(2016-10-07)
Adamson, P.
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An, F. P.
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Anghel, I.
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Aurisano, A.
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Balantekin, A. B.
Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti) neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin(2) 2 theta(mu e) are set over 6 orders of magnitude in the sterile mass-squared splitting Delta m(41)(2). The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Delta m(41)(2) < 0.8 eV(2) at 95% CLs.
Measurement of Cosmic-ray Muon-induced Spallation Neutrons in the Aberdeen Tunnel Underground Laboratory
(2016-04-01)
Blyth, S. C.
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Chan, Y. L.
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Chen, X. C.
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Chu, M. C.
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Cui, K. X.
Muon-induced neutrons are one of the major backgrounds to various underground experiments, such as dark matter searches, low-energy neutrino oscillation experiments and neutrino-less double beta-decay experiments. Previous experiments on the underground production rate of muon-induced neutrons were mostly carried out either at shallow sites or at very deep sites. The Aberdeen Tunnel experiment aims to measure the neutron production rate at a moderate depth of 611 meters water equivalent. Our apparatus comprises of six layers of plastic-scintillator hodoscopes for tracking the incident cosmic-ray muons, and 760 L of gadolinium-doped liquid-scintillator for both neutron production and detection targets. In this paper, we describe the design and the performance of the apparatus. The preliminary result on the measurement of neutron production rate is also presented.
Measurement of Cosmic-ray Muon-induced Spallation Neutrons in the Aberdeen Tunnel Underground Laboratory
(2016-04-06)
Blyth, S. C.
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Chan, Y. L.
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Chen, X. C.
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Chu, M. C.
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Cui, K. X.
Muon-induced neutrons are one of the major backgrounds to various underground experiments, such as dark matter searches, low-energy neutrino oscillation experiments and neutrino-less double beta-decay experiments. Previous experiments on the underground production rate of muon-induced neutrons were mostly carried out either at shallow sites or at very deep sites. The Aberdeen Tunnel experiment aims to measure the neutron production rate at a moderate depth of 611 meters water equivalent. Our apparatus comprises of six layers of plastic-scintillator hodoscopes for tracking the incident cosmic-ray muons, and 760 L of gadolinium-doped liquid-scintillator for both neutron production and detection targets. In this paper, we describe the design and the performance of the apparatus. The preliminary result on the measurement of neutron production rate is also presented.
Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory
(2016-04-07)
Blyth, S. C.
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Chan, Y. L.
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Chen, X. C.
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Chu, M. C.
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Cui, K. X.
We have measured the muon flux and production rate of muon-induced neutrons at a depth of 611 m water equivalent. Our apparatus comprises three layers of crossed plastic scintillator hodoscopes for tracking the incident cosmic-ray muons and 760 L of a gadolinium-doped liquid scintillator for producing and detecting neutrons. The vertical muon intensity was measured to be I-mu = (5.7 +/- 0.6) x 10(-6) cm(-2) s(-1) sr(-1). The yield of muon-induced neutrons in the liquid scintillator was determined to be Y-n = (1.19 +/- 0.08(stat) +/- 0.21(syst)) x 10(-4) neutrons/(mu.g.cm(-2)). A fit to the recently measured neutron yields at different depths gave a mean muon energy dependence of < E-mu >(0.76 +/- 0.03) for liquid-scintillator targets.
Measurement of cosmic-ray muons and muon-induced neutrons in the Aberdeen Tunnel Underground Laboratory (vol 93, 072005, 2016)
(2016-11-28)
Blyth, S. C.
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Chan, Y. L.
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Chen, X. C.
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Chu, M. C.
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Cui, K. X.
Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment
(2017-04-06)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GWth nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of nu((e) over bar)'s. Comparison of the (v) over bare rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (similar to 1500-1950 m) relative to detectors near the reactors (similar to 350-600 m) allowed a precise measurement of (v) over bar (e) disappearance. More than 2.5 million (v) over bar (e) inverse beta-decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (December, 2011-July, 2012) with a subsequent 1013 days using the complete configuration of eight detectors (October, 2012-July, 2015). The (v) over bar (e) rate observed at the far detectors relative to the near detectors showed a significant deficit, R = 0.949 +/- 0.002(stat) +/- 0.002(syst). The energy dependence of (v) over bar (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(2)2 theta(13) = 0.0841 +/- 0.0027(stat) +/- 0.0019(syst) and the effective neutrino mass-squared difference of broken vertical bar Delta m(ee)(2)vertical bar = (2.50 +/- 0.06(stat) +/- 0.06(syst)) x 10(-3) eV(2). Analysis using the exact three-flavor probability found Delta m(32)(2) = (2.45 +/- 0.06(stat) +/- 0.06d(syst)) x 10(-3) eV(2) assuming the normal neutrino mass hierarchy and Delta m(32)(2) = (-2.56 +/- 0.06(stat) +/- 0.06(syst)) x 10(-3) eV(2) for the inverted hierarchy.
Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay
(2016-02-12)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
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 and 561 m) and one far (1579 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 +/- 0.04) x 10(-18) cm(2) GW(-1) day(-1) or (5.92 +/- 0.14) x 10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946 +/- 0.022 (0.991 +/- 0.023) 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 similar to 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.
New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay
(2015-09-11)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
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 x 10(5) GW(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 Am-241-C-13 radioactive calibration sources reduced the background by a factor of 2 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 vertical bar Delta m(ee)(2)vertical bar were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin(2)2 theta(13) = 0.084 +/- 0.005 and vertical bar Delta m(ee)(2)vertical bar = (2.42 +/- 0.11) x 10(-3) eV(2) in the three-neutrino framework.
New measurement of theta(13) via neutron capture on hydrogen at Daya Bay
(2016-04-21)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
This article reports an improved independent measurement of neutrino mixing angle theta(13) at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse beta-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 Li-9 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(2)2 theta(13) = 0.071 +/- 0.011 in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.
Observation of Electron-Antineutrino Disappearance at Daya Bay
(2012-04-23)
An, F. P.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
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Beavis, D.
The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle 0(13) with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW(th) reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43 000 ton-GW(th)-day live-time exposure in 55 days, 10 416 (80 376) electron-antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is R = 0.940 +/- 0.011(stat.) +/- 0.004(syst.). A rate-only analysis finds sin(2)2 theta(13) = 0.092 +/- 0.016(stat.) +/- 0.005(syst.) in a three-neutrino framework.
Results from the Daya Bay Reactor Neutrino Experiment
(2014-01-01)
Tsang, K. V.
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An, F. P.
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An, Q.
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Bai, J. Z.
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Balantekin, A. B.
The Daya Bay Reactor Neutrino Experiment was designed to achieve a sensitivity on the value of sin(2) 2 theta(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) 2 theta(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) 2 theta(13) = 0.089 +/- 0.010(stat.) +/- 0.005(syst.), which is the most precise measurement of sin(2) 2 theta(13) to date.
Search for a Light Sterile Neutrino at Daya Bay
(2014-10-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2) < vertical bar Delta m(41)(2)vertical bar < 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2 theta(14) cover the 10(-3) eV(2) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.1 eV(2) region, which was largely unexplored.