Analysis of the Results of the Neutrino-4 Experiment on the Search for the Sterile Neutrino and Comparison with Results
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PARTICLES, AND NUCLEI
Analysis of the Results of the Neutrino-4 Experiment on the Search for the Sterile Neutrino and Comparison with Results of Other Experiments A. P. Serebrova, * and R. M. Samoilova a
Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, Gatchina, 188300 Russia *e-mail: [email protected] Received March 23, 2020; revised July 6, 2020; accepted July 7, 2020
New measurements of the flux and spectrum of reactor antineutrinos as functions of the distance from the center of the core of the SM-3 reactor (Dimitrovgrad, Russia) in the range of 6–12 m have been reported. Additional measurements have been performed. The amount of experimental data has been increased by almost a factor of 2. The model-independent analysis has been performed in order to determine the oscilla2 tion parameters Δm14 and sin 2 2θ14 . The method of coherent addition of measurement results allows the direct demonstration of the effect of oscillations. The effect of oscillations is observed near the values 2 Δm14 = 7.25 ± 0.13st ± 1.08sys and sin 2 2θ = 0.26 ± 0.08stat ± 0.05syst . This result has been compared to the results of other experiments on the search for the sterile neutrino. The joint analysis of the Neutrino-4 experiment with the gallium and reactor anomalies gives the value sin 2 2θ14 ≈ 0.19 ± 0.04 (4.6σ) . The results of the Neutrino-4 experiment have been compared to the results of the NEOS, DANSS, STEREO, and PROSPECT reactor experiments; MiniBooNE and LSND accelerator experiments; and IceCube experi2 ment. According to the Neutrino-4 experiment (under the assumption that m42 ≈ Δm14 ) , the mass of the sterile neutrino is m4 = (2.68 ± 0.13 ) eV. The calculations with the estimates of the mixing angles from other eff experiments give the values mveff = (0.58 ± 0.09) eV, mveff = (0.42 ± 0.24) eV, and mvτ ≤ 0.65 eV for the e μ masses of the electron, muon, and tau neutrinos, respectively. The extended Pontecorvo–Maki–Nakagawa– Sakata matrix for the 3 + 1 model with one sterile neutrino is given.
DOI: 10.1134/S0021364020160122
P (νe → νe )
1. INTRODUCTION The experimental search for possible neutrino oscillations to the sterile state has been performed for many years, including experiments at accelerators, reactors, and artificial neutrino sources [1–24]. Sterile neutrinos are candidates for dark matter particles. The hypothesis of oscillations to the sterile state can be tested by the direct measurement of the dependence of the neutrino flux and neutrino energy spectrum on the distance in the range of 6–12 m. This method of relative measurements can be more accurate. To this end, a detector should be mobile and spectrally sensitive. To observe oscillations to the sterile state, it is necessary to detect the deviation of the distance dependence of the neutron flux from the 1/L2 law and the variation of the spectrum shape with the distance. If oscillations to the sterile state indeed occur, they can be described at short distances by the formula
(1) Δm2 [eV 2 ]L[m] 2 2 = 1 − s
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