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Register a new userFuel-composition dependent reactor antineutrino yield at RENO
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The RENO Collaboration
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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.
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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.
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$^2$.
The Reactor Experiment for Neutrino Oscillation (RENO) experiment has been taking data using two identical liquid scintillator detectors of 44.5 tons since August 2011. The experiment has observed the disappearance of reactor neutrinos in their interactions with free protons, followed by neutron capture on hydrogen. Based on 1500 live days of data taken with 16.8 GW$_{th}$ reactors at the Hanbit Nuclear Power Plant in Korea, the near (far) detector observes 567690 (90747) electron antineutrino candidate events with a delayed neutron capture on hydrogen. This provides an independent measurement of $theta_{13}$ and a consistency check on the validity of the result from n-Gd data. Furthermore, it provides an important cross-check on the systematic uncertainties of the n-Gd measurement. Based on a rate-only analysis, we obtain sin$^{2}$2$theta _{13}$= 0.087 $pm$ 0.008 (stat.) $pm$ 0.014 (syst.).
Neutrinos are elementary particles in the standard model of particle physics. There are 3 flavors of neutrinos that oscillate among themselves. Their oscillation can be described by a 3$times$3 unitary matrix, containing three mixing angles $theta_{12}$, $theta_{23}$, $theta_{13}$, and one CP phase. Both $theta_{12}$ and $theta_{23}$ are known from previous experiments. $theta_{13}$ was unknown just two years ago. The Daya Bay experiment gave the first definitive non-zero value in 2012. An improved measurement of the oscillation amplitude $sin^{2}2(theta_{13})$ = $0.090^{+0.008}_{-0.009}$ and the first direct measurement of the $bar u_{e}$ mass-squared difference $mid$$Delta m^2_{ee}$$mid$ = $(2.59^{+0.19}_{-0.20})times10^{-3} rm eV^{2}$ were obtained recently. The large value of $theta_{13}$ boosts the next generation of reactor antineutrino experiments designed to determine the neutrino mass hierarchy, such as JUNO and RENO-50 .
Recently new reactor antineutrino spectra have been provided for 235U, 239Pu, 241Pu and 238U, increasing the mean flux by about 3 percent. To good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances <100 m leads to a ratio of observed event rate to predicted rate of 0.976(0.024). With our new flux evaluation, this ratio shifts to 0.943(0.023), leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-neutrino data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |Delta m_{new}^2|>1.5 eV^2 (95%) and sin^2(2theta_{new})=0.14(0.08) (95%). Constraints on the theta13 neutrino mixing angle are revised.
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