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Register a new userExperiment Neutrino-4 search for sterile neutrino and results of measurements
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The experiment Neutrino-4 had started in 2014 with a detector model and then was continued with a full-scale detector in 2016 - 2021. In this article we describe all steps of 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 $Delta m_{14}^2$ and $sin^22theta_{14}$. The method of coherent summation of measurement results allows 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 $2.9sigma$ level with parameters $Delta m_{14}^2=(7.3pm0.13_{st}pm1.16_{sys})text{eV}^2 = (7.3pm1.17)text{eV}^2$ and $sin^22theta_{14}= 0.36pm0.12_{stat}(2.9sigma)$. Monte Carlo based statistical analysis gave estimation of confidence level at $2.7sigma$. 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.
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An experiment to search for light sterile neutrinos was conducted at a reactor with a thermal power of 2.8 GW located at the Hanbit nuclear power complex. The search was done with a detector consisting of a ton of Gd-loaded liquid scintillator in a tendon gallery approximately 24 m from the reactor core. The measured antineutrino event rate is 1976 per day with a signal to background ratio of about 22. The shape of the antineutrino energy spectrum obtained from eight-month data-taking period is compared with a hypothesis of oscillations due to active-sterile antineutrino mixing. It is found to be consistent with no oscillation. An excess around 5 MeV prompt energy range is observed as seen in existing longer baseline experiments. The parameter space of $sin^{2}2theta_{14}$ down below 0.1 for $Delta m^{2}_{41}$ ranging from 0.2 eV$^{2}$ to 2.3 eV$^{2}$ and the optimum point for the previously reported reactor antineutrino anomaly are excluded with a confidence level higher than 90%.
We present the results of the Neutrino-4 experiment on search for a sterile neutrino. The experiment has been carried out on the SM-3 reactor having a compact active zone of $42times42times35textrm{cm}^3$ and operating on the highly enriched uranium-235 at 90 MW thermal power. We report the results of the Neutrino-4 experiment 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. Using the measured spectrum and the distance dependence of antineutrino flux, we performed the model independent analysis of restrictions on the oscillation parameters $Delta m^2_{14}$ and $sin^2 2theta_{14}$. The method of coherent addition of results of measurements is proposed. It allows us to directly observe the effect of oscillations. We observed the oscillation effect at CL $3.5sigma$ in the vicinity of $Delta m^2_{14} approx 7.26textrm{eV}^2$ and $sin^2 2theta_{14} approx 0.38$. Combining the result of the Neutrino-4 experiment and the result of the gallium anomaly effect we obtained value $sin^2 2theta_{14} approx 0.35 pm 0.07 (5sigma)$. The analysis of systematics effects is presented. Comparison with results of other experiments is presented. Future prospect of the experiment is discussed. It is necessary to notice that obtained values $sin^2 2theta_{14} approx 0.35 pm 0.07 (5sigma)$ and $Delta m^2_{14} approx (7.3 pm 0.7)textrm{eV}^2$ allow make assessment on the mass of a neutrino: $m_{beta} approx 0.8textrm{eV}$.
In order to carry out research in the field of possible existence of a sterile neutrino the laboratory based on SM-3 reactor (Dimitrovgrad, Russia) was created to search for oscillations of reactor antineutrino. A moveable detector, protected with passive shielding from outer radiation, can be set at distance range 6 to 12 meters from the reactor core. Measurements of antineutrino flux at such short distances from the reactor core are carried out with moveable detector for the first time. The main difficulties of the measurements caused by cosmic background and it heavily decreases the precision of measurements. We present the analysis of measurements at small distances together with the data obtained in measurements at long distances in order to obtain parameters of sterile neutrino.
We comment on the claimed observation [arXiv:arXiv:2005.05301] of sterile neutrino oscillations by the Neutrino-4 collaboration. Such a claim, which requires the existence of a new fundamental particle, demands a level of rigor commensurate with its impact. The burden lies with the Neutrino-4 collaboration to provide the information necessary to prove the validity of their claim to the community. In this note, we describe aspects of both the data and analysis method that might lead to an oscillation signature arising from a null experiment and describe additional information needed from the Neutrino-4 collaboration to support the oscillation claim. Additionally, as opposed to the assertion made by the Neutrino-4 collaboration, we also show that the method of coherent summation using the $L/E$ parameter produces similar results to the methods used by the PROSPECT and the STEREO collaborations.
The experiment Neutrino-4 started in 2014 on a model, then it was continued on a full-scale detector, and now, has provided the measurement result on dependence of the flux and spectrum of reactor antineutrinos on the distance of 6 - 12 meters from the center of the reactor. One of the main problems is the correlated background from fast neutrons caused by space radiation. Attempts to suppress the background of fast neutrons by sectioning the detector have given some result. The relation of effect/background has improved up to 0.6. As a result, measurements of the difference in the counting rate of neutrino-like events (reactor ON - reactor OFF) have been obtained as dependence on distance from the reactor center. The fit of experimental dependence with the law $1/L^2$ give satisfactory result. The goodness of that fit is 81%. However, there was discovered experimental neutrino spectrum difference from calculated one. With achieved accuracy this difference does not change with distance. Therefore it cannot be interpreted as oscillations. Calculated spectrum form correction for experimental allow us to make proper analysis of oscillation parameters $Delta m^2_{14}$ and $sin^2(2theta)$ limitations. Result of this analysis is exclusion of reactor and gallium anomalies area with 95% CL. Experiment future perspectives are discussed.
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