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Register a new userMeasurement of Reactor Antineutrino Flux and Spectrum at RENO
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The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos,($overline{ u}_e$) from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966,094,(116,111),$overline{ u}_e$ 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 $overline{ u}_e$ 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 $overline{ u}_e$ 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 $overline{ u}_e$ models.
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The RENO experiment reports more precisely measured values of $theta_{13}$ and $|Delta m_{ee}^2|$ using $sim$2,200 live days of data. The amplitude and frequency of reactor electron antineutrino ($overline{ u}_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) electron antineutrino candidate events with a background fraction of 4.7% (2.0%). A clear energy and baseline dependent disappearance of reactor $overline{ u}_e$ is observed in the deficit of the measured number of $overline{ u}_e$. Based on the measured far-to-near ratio of prompt spectra, we obtain $sin^2 2 theta_{13} = 0.0896 pm 0.0048({rm stat}) pm 0.0048({rm syst})$ and $|Delta m_{ee}^2| =[2.68 pm 0.12({rm stat}) pm 0.07({rm syst})]times 10^{-3}$~eV$^2$.
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 $0.946pm0.022$ ($0.991pm0.023$) 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.
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 $0.946pm0.020$ ($0.992pm0.021$) 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.
We report a fuel-dependent reactor electron antineutrino ($overline{ u}_e$) yield using six 2.8 GW$_{text{th}}$ reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses $850,666$ $overline{ u}_e$ 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 pm 0.23) times 10^{-43} $cm$^2$/fission and measure a total average IBD yield of $(5.84 pm 0.13) times 10^{-43} $cm$^2$/fission. The hypothesis of no fuel-dependent IBD yield is ruled out at 6.6 $sigma$. The observed IBD yield variation over $^{235}$U isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at 1.3 $sigma$. The measured fuel-dependent variation determines IBD yields of $(6.15 pm 0.19) times 10^{-43} $cm$^2$/fission and $(4.18pm 0.26) times 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 of the anomaly. We also report a 2.9 $sigma$ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of $^{235}$U.
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$_{textrm{th}}$ reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective $^{239}$Pu fission fractions, $F_{239}$, from 0.25 to 0.35, Daya Bay measures an average IBD yield, $bar{sigma}_f$, of $(5.90 pm 0.13) times 10^{-43}$ cm$^2$/fission and a fuel-dependent variation in the IBD yield, $dsigma_f/dF_{239}$, of $(-1.86 pm 0.18) times 10^{-43}$ cm$^2$/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the $^{239}$Pu fission fraction at 10 standard deviations. The variation in IBD yield was 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 measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes $^{235}$U, $^{239}$Pu, $^{238}$U, and $^{241}$Pu. Based on measured IBD yield variations, yields of $(6.17 pm 0.17)$ and $(4.27 pm 0.26) times 10^{-43}$ cm$^2$/fission have been determined for the two dominant fission parent isotopes $^{235}$U and $^{239}$Pu. A 7.8% discrepancy between the observed and predicted $^{235}$U yield suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly.
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