The experiment Neutrino-4 started in 2014 with a detector model and continued with a full-scale detector in 2016–2021. In this article, we describe all the steps of the preparatory work on this experiment. We present all results of the Neutrino-4 experiment with increased statistical accuracy provided to date. The experimental setup is constructed to measure the flux and spectrum of the reactor antineutrinos as a function of distance to the center of the active zone of the SM-3 reactor (Dimitrovgrad, Russia) in the range of 6–12 meters. Using all the collected data, we performed a model-independent analysis to determine the oscillation parameters $\mathrm{\Delta }{\mathrm{m}}_{14}^2$ and ${\sin }^{2}2{\theta }_{14}$. The method of coherent summation of measurement results allows us to directly demonstrate the oscillation effect. We present the analysis of possible systematic errors and the MC model of the experiment, which considers the possibility of the effect manifestation at the present precision level. As a result of the analysis, we can conclude that at currently available statistical accuracy, we observe the oscillations at the $2.9\sigma$ level with the parameters $\mathrm{\Delta }{m}_{14}^2=(7.3\pm {0.13}_{\mathrm{st}}\pm {1.16}_{\mathrm{syst}}){\mathrm{eV}}^2=(7.3\pm 1.17){\mathrm{eV}}^2$ and ${\sin }^{2}2\theta =0.36\pm {0.12}_{\mathrm{stat}}(2.9\sigma )$. Monte Carlo based statistical analysis gave an estimation of the confidence level at $2.7\sigma$. We plan to improve the currently working experimental setup and create a completely new setup in order to increase the accuracy of the experiment by 3 times. We also provide a brief analysis of the general experimental situation in the search for sterile neutrinos.

• Received 22 May 2020
• Revised 5 April 2021
• Accepted 15 June 2021

DOI:https://doi.org/10.1103/PhysRevD.104.032003

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Published by the American Physical Society