Abstract
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 $\mathrm{\ensuremath{\Delta}}{\mathrm{m}}_{14}^{2}$ and ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{14}$. 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 $2.9\ensuremath{\sigma}$ level with the parameters $\mathrm{\ensuremath{\Delta}}{m}_{14}^{2}=(7.3\ifmmode\pm\else\textpm\fi{}{0.13}_{\mathrm{st}}\ifmmode\pm\else\textpm\fi{}{1.16}_{\mathrm{syst}})\text{ }\text{ }{\mathrm{eV}}^{2}=(7.3\ifmmode\pm\else\textpm\fi{}1.17)\text{ }\text{ }{\mathrm{eV}}^{2}$ and ${\mathrm{sin}}^{2}2\ensuremath{\theta}=0.36\ifmmode\pm\else\textpm\fi{}{0.12}_{\mathrm{stat}}(2.9\ensuremath{\sigma})$. Monte Carlo based statistical analysis gave an estimation of the confidence level at $2.7\ensuremath{\sigma}$. 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.
Highlights
Experiments on the search for possible neutrino oscillations in a sterile state have been carried out for many years
As a result of the analysis, we can conclude that at currently available statistical accuracy, we observe the oscillations at the 2.9σ level with the parameters Δm214 1⁄4 ð7.3 Æ 0.13st Æ 1.16systÞ eV2 1⁄4 ð7.3 Æ 1.17Þ eV2 and sin22θ 1⁄4 0.36 Æ 0.12statð2.9σÞ
The model of the detector was applied to investigate the method of antineutrino registration as a result of the inverse beta decay (IBD) process as well as the effectiveness of active shielding to suppress the background of cosmic rays
Summary
Experiments on the search for possible neutrino oscillations in a sterile state have been carried out for many years. Studies of the cosmic ray background were carried out with a test model of a neutrino detector filled with 400 liters of a gadolinium-doped liquid scintillator (0.1% Gd) and covered with the active shielding against cosmic muons The model of the detector was applied to investigate the method of antineutrino registration as a result of the inverse beta decay (IBD) process as well as the effectiveness of active shielding to suppress the background of cosmic rays. XVII–XIX, we discuss the spectrum independent method for analysis of the neutrino signal and the Monte Carlo simulations of this method This is an extremely important point that allows us to move to real measurements and to process the results in order to reveal possible neutrino oscillations at short distances. This analysis is of great importance because it ensures that the obtained result does not contradict the results of other experiments on the search for sterile neutrinos
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