Analysis of the Results of the Neutrino-4 Experiment on the Search for the Sterile Neutrino and Comparison with Results of Other Experiments

Abstract

We present new results of measurements of reactor antineutrino flux and spectrum dependence on the distance in the range 6-12 meters from the center of the reactor core at SM-3 reactor (Dimitrovgrad, Russia). Additional measurements were carried out and set of data to perform statistical analysis was almost doubled since the previous report. Using all collected data, we performed the model independent analysis on the oscillation parameters ∆m 14 2 and sin 2 2𝜃 14 . The method of coherent summation of results of measurements allows us to directly observe the effect of oscillations. We observed an oscillation effect at CL 3.0𝜎 in vicinity of ∆m 14 2 ≈ 7.25eV 2 and sin 2 2θ 14 ≈ 0.26 ± 0.08(3.0)σ. We provide a comparison of our results with results of other experiments on search for sterile neutrino. Combining the result of the Neutrino-4 experiment and the results of measurements of the gallium anomaly and reactor anomaly we obtained value sin 2 2θ 14 ≈ 0.19 ± 0.04 (4.6σ). Also was performed comparison of Neutrino-4 experimental results with results of other reactor experiments NEOS, DANSS, STEREO, PROSPECT and accelerator experiments MiniBooNE, LSND and results of the IceCube experiment. Sterile neutrino mass which can be calculated using the Neutrino-4 data in assumption that m 4 2 ≈ Δm 14 2 is m 4 = (2.68 ± 0.13)eV. Considering estimations of mixing angles obtained in other experiments we can calculate masses of electron neutrino, muon neutrino and tau neutrino: m 𝜈 𝑒 eff = (0.58 ± 0.09)eV, m 𝜈 𝜇 eff = (0.42 ± 0.24)eV, m 𝜈 𝜏 eff ≤ 0.65eV

Statistical interpretation of sterile neutrino oscillation searches at reactors

“…The Neutrino-4 experiment [16,30] has recently claimed a possible indication of sterile neutrino oscillations with Δm 2 7.2 eV 2 and sin 2 2θ 0.26. They report a statistical significance using their combined phase 1 and 2 data [30]. Then an estimate of their systematic uncertainty is quoted, leading to a combined statistical/systematical significance of a positive sin 2 2θ of 2.8σ .…”

“…Neutrino-4 uses a segmented detector, which allows to bin their data in both L and E. The data is binned using 9 bins in energy with width ΔE = 0.5 MeV starting at 2.3 MeV, and 24 bins in baseline with ΔL = 0.235 m starting at 6.25 m, resulting into a total of 216 bins in L/E. The bin width in energy of 0.5 MeV corresponds to the energy resolution of the detector [30]. Eventually, each consecutive group of 8 bins are combined together, leading to N = 27 data points.…”

“…Out of these, the first 19 bins are shown for the combined phase 1 and phase 2 data sets in Fig. 47 of [30] (blue points). Following the Neutrino-4 collaboration, we fit these 19 data points with the survival probability for a given L/E bin over the averaged probability:…”

“…The fit is performed with a simple Gaussian χ 2 definition, using the statistical uncertainties read off from Fig. 47 of [30]. Note that, due to the particular way the fit is performed by Neutrino-4, using the ratios in Eqs.…”

“…In Sect. 6 we consider as a case study the recent results for the Neutrino-4 experiment [16,30], which has reported a ∼ 3σ hint for sterile neutrino oscillations. We perform a Monte-Carlo study of the Neutrino-4 data and show that the significance for the presence of sterile neutrinos is somewhat lower than expected under the assumption of a χ 2 distribution of the test statistics, and we present the confidence regions obtained by explicit Neyman-Pearson construction based on the Feldman-Cousins prescription [31].…”