Browsing by Author "Adey, D."

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A high precision calibration of the nonlinear energy response at Daya Bay
(2019-10-01)
Adey, D.
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An, F. P.
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Balantekin, A. B.
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Band, H. R.
;
Bishai, M.
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.. calibration points from deployed and naturally occurring radioactive sources, the.. spectrum from B-12 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.
Extraction of the U-235 and Pu-239 Antineutrino Spectra at Daya Bay
(2019-09-13)
Adey, D.
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An, F. P.
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Balantekin, A. B.
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Band, H. R.
;
Bishai, M.
This Letter reports the first extraction of individual antineutrino spectra from U-235 and Pu-239 fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses 3.5 x 10(6) inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, U-235 and Pu-239, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4-6 MeV, a 7% (9%) excess of events is observed for the U-235 (Pu-239) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is 4.0 sigma for U-235 spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at 5.3 sigma. In the energy range of 4-6 MeV, a maximal local discrepancy of 6.3 sigma is observed.
Improved measurement of the reactor antineutrino flux at Daya Bay
(2019-09-09)
Adey, D.
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An, F. P.
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Balantekin, A. B.
;
Band, H. R.
;
Bishai, M.
This work reports a precise measurement of the reactor antineutrino flux using 2.2 million inverse beta decay (IBD) events collected with the Daya Bay near detectors in 1230 days. The dominant uncertainty on the neutron detection efficiency is reduced by 56% with respect to the previous measurement through a comprehensive neutron calibration and detailed data and simulation analysis. The new average IBD yield is determined to be (5.91 +/- 0.09) x 10(-43) cm(2)/fission with total uncertainty improved by 29%. The corresponding mean fission fractions from the four main fission isotopes U-235, U-238, Pu-239, and( 241)Pu are 0.564, 0.076, 0.304, and 0.056, respectively. The ratio of measured to predicted antineutrino yield is found to be 0.952 +/- 0.014 +/- 0.023 (1.001 +/- 0.015 +/- 0.027) for the Huber-Mueller (ILL-Vogel) model, where the first and second uncertainty are experimental and theoretical model uncertainty, respectively. This measurement confirms the discrepancy between the world average of reactor antineutrino flux and the Huber-Mueller model.
Measurement of the Electron Antineutrino Oscillation with 1958 Days of Operation at Daya Bay
(2018-12-14)
Adey, D.
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An, F. P.
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Balantekin, A. B.
;
Band, H. R.
;
Bishai, M.
We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor (nu) over bar (e) inverse beta decay candidates observed over 1958 days of data collection. The installation of a flash analog-to-digital converter 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 Li-9 and He-8 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 (nu) over bar (e) rates and energy spectra among detectors yields sin(2)2 theta(13) = 0.0856 +/- 0.0029 and Delta m(32)(2) = (2.471(-0.070)(+0.068)) x 10(-3) eV(2) assuming the normal hierarchy, and Delta m(32)(2) = -(2.575(-0.070)(+0.068)) x 10(-3) eV(2) assuming the inverted hierarchy.
Search for a time-varying electron antineutrino signal at Daya Bay
(2018-11-20)
Adey, D.
;
An, F. P.
;
Balantekin, A. B.
;
Band, H. R.
;
Bishai, M.
A search for a time-varying (nu) over bar (e) signal was performed with 621 days of data acquired by the Daya Bay Reactor Neutrino Experiment over 704 calendar days. The time spectrum of the measured (nu) over bar (e) flux normalized to its prediction was analyzed with a Lomb-Scargle periodogram, which yielded no significant signal for periods ranging from 2 hours to nearly 2 years. The normalized time spectrum was also fit for a sidereal modulation under the Standard Model Extension (SME) framework to search for Lorentz and CPT violation (LV-CPTV). Limits were obtained for all six flavor pairs (e) over bar(mu) over bar, (e) over bar(tau) over bar, (mu) over bar(tau) over bar, (e) over bar(e) over bar, (mu) over bar(mu) over bar and (tau) over bar(tau) over bar by fitting them one at a time, constituting the first experimental constraints on the latter three. Daya Bay's high statistics and unique layout of multiple directions from three pairs of reactors to three experimental halls allowed the simultaneous constraint of individual SME LV-CPTV coefficients without assuming others contribute negligibly, a first for a neutrino experiment.