The RENO experiment has analyzed about 500 live days of data to observe an energy dependent disappearance of reactor νe by comparison of their prompt signal spectra measured in two identical near and far detectors. In the period between August 2011 and January 2013, the far (near) detector observed 31541 (290775) electron antineutrino candidate events with a background fraction of 4.9% (2.8%). The measured prompt spectra show an excess of reactor νe around 5 MeV relative to the prediction from a most commonly used model. A clear energy and baseline dependent disappearance of reactor νe is observed in the deficit of the observed number of νe. Based on the measured far-to-near ratio of prompt spectra, we obtain sin 2 2θ13 = 0. The reactor ν e disappearance has been firmly observed to determine the smallest neutrino mixing angle θ 13 [1-3]. All of the three mixing angles in the Pontecorvo-MakiNakagawa-Sakata matrix [4,5] have been measured to provide a comprehensive picture of neutrino transformation. The successful measurement of a rather large θ 13 value opens the possibility of searching for CP violation in the leptonic sector and determining the neutrino mass ordering. Appearance of ν e from an accelerator ν µ beam is also observed by the T2K [6] and NOνA [7] experiments.Using the ν e survival probability P [8], reactor experiments with a baseline distance of ∼1 km can determine the mixing angle θ 13 and an effective squared-massdifference ∆m where ∆ ij ≡ 1.267∆m 2 ij L/E, E is the ν e energy in MeV, and L is the distance between the reactor and detector in meters.The first measurement of θ 13 by RENO was based on the rate-only analysis of deficit found in ∼220 live days of data [1]. The oscillation frequency |∆m 2 ee | in the measurement was approximated by the measured value |∆m 2 31 | assuming the normal ordering in the ν µ disappearance [10]. In this Letter, we present a more precisely measured value of θ 13 and our first determination of |∆m 2 ee |, based on the rate, spectral and baseline information (rate+spectrum analysis) of reactor ν e disappearance using ∼500 live days of data. The Daya Bay collaboration has also reported spectral measurements [11].The RENO uses identical near and far ν e detectors located at 294 m and 1383 m, respectively, from the center of six reactor cores of the Hanbit (known as Yonggwang) Nulcear Power Plant. The far (near) detector is under a 450 m (120 m) of water equivalent overburden. Six pressurized water reactors, each with maximum thermal output of 2.8 GW th , are situated in a linear array spanning 1.3 km with equal spacings. The reactor flux-weighted baseline is 410.6 m for the near detector and 1445.7 m for the far detector.The reactor ν e is detected through the inverse beta decay (IBD) interaction, ν e + p → e + + n, with free protons in hydrocarbon liquid scintillator (LS) with 0.1% Gadolinium (Gd) as a target. The coincidence of a prompt positron signal and a mean time of ∼28 µs delayed signal from neutron capture by Gd (n-Gd) provides the distinctive IBD signatur...
The RENO experiment reports more precisely measured values of θ13 and |∆m 2 ee | using ∼2 200 live days of data. The amplitude and frequency of reactor electron antineutrino (νe) 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) νe candidate events with a background fraction of 4.8% (2.0%). A clear energy and baseline dependent disappearance of reactor νe is observed in the deficit of the measured number of νe. Based on the measured far-to-near ratio of prompt spectra, we obtain sin 2 2θ13 = 0.0896 ± 0.0048(stat) ± 0.0047(syst) and |∆m 2 ee | = [2.68 ± 0.12(stat) ± 0.07(syst)] × 10 −3 eV 2 .
New developments in liquid scintillators, highefficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could reconstruct particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated deep underground, and utilizing new techniques in computing and reconstruction, this detector could achieve unprecedented levels of background rejection, enabling a rich physics program spanning topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low-and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP-violating phase δ, observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for neutrinoless double beta decay, with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia, a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above.
The Reactor Experiment for Neutrino Oscillation (RENO) has been taking electron antineutrino (ν e ) data from the reactors in Yonggwang, Korea, using two identical detectors since August 2011. Using roughly 500 live days of data through January 2013 we observe 290 775 (31 514) reactorν e candidate events with 2.8% (4.9%) background in the near (far) detector. The observed visible positron spectra from the reactorν e events in both detectors show a discrepancy around 5 MeV with regard to the prediction from the current reactorν e model. Based on a far-to-near ratio measurement using the spectral and rate information, we have obtained sin 2 2θ 13 ¼ 0.082 AE 0.009ðstat:Þ AE 0.006ðsyst:Þ and jΔm
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