The optimization of the neutron guide system of a new ultracold neutron source based on superfluid helium for fundamental interaction physics research at the PIK reactor is considered. In the current configuration, it is planned to achieve a UCN density of 950 cm–3 in the closed converter chamber. After the upgrade, replacing the steel heat exchanger with a copper one can increase the UCN density in the closed converter chamber to 3400 cm–3. Monte Carlo simulations for the new source to calculate the UCN densities in the closed converter chamber and at the splitter outlet for future users planning experiments at this source are performed. In the simulations, the entire geometry and components of the neutron guide system are taken into account. The results show a steady-state density in the 10-L trap at the splitter outlet of 340 cm–3 after the heat exchanger upgrade.

An analysis of the latest, most accurate experimental data on neutron decay points to the need to extend the Standard Model by introducing a right vector boson admixture W_R. A left-right asymmetry model of the weak interaction is presented, in which the sign of the mixing angle W_R and W_L is reversed upon transition from W^- to W^+. In this model, CP violation occurs due to the presence of a right vector boson admixture. The model parameter, the mixing angle, ζ=-(2.7±0.9)·10^-3 is derived from neutron decay - lifetime and decay asymmetries - as well as from studies of proton decay in nuclei, the so-called superallowed 0^+-0^+ transitions. An estimate for the mass W_R M_W_R=(340±60) GeV is given by the relation: from the parameter δ=(5.5±1.8)·10^-2, which is the ratio of the squares of the mass states of vector bosons. The possibility of describing CP-violation effects in neutral meson oscillations within the left-right asymmetry weak interaction model with parameters δ and ζ is investigated. It is shown that within this model, CP violation effects in the decays of K^0-mesons, D^0-mesons, B^0-mesons, and B^0_s-mesons can be successfully described. Moreover, the sign of CP violation is opposite for particles and antiparticles, i.e., the CP violation phase is equal to /2, which corresponds to 100

At the Petersburg Nuclear Physics Institute (PNPI) of the National Research Center “Kurchatov Institute”, the work is underway to manufacture an ultracold neutron (UCN) source, in which superfluid helium is used as a converter, for research in physics of fundamental interactions. The UCN density in the closed chamber of the source is expected to be at a level of 3.4 × 103 cm–3. This source will provide the operation with four experimental setups sequentially. The efficient transport of UCN towards experiments will be achieved using neutron guides of stainless steel with an internal diameter of 125 mm. The manufacturing technology for these neutron guides is described, in particular the polishing and the deposition of a thin 58Ni film on the inner surface.

The Neutron Beta Decay Instrument Complex is part of the PIK reactor complex (RC) instrumentation. The setup is designed to measure the electron, neutrino, and electron–neutrino asymmetries of neutron beta decay with an accuracy of 0.1

An analysis of the latest, most accurate experimental data on neutron decay indicates the need to expand the Standard Model by introducing an admixture of the right vector boson W_R with a mixing angle of ζ= -0.039±0.014 with the left vector boson W_L and a ratio of the squares of the masses of W_1 and W_2 equal to δ= 0.070±0.010. In this regard, the possibility of describing CP-violation effects in neutral meson oscillations within the framework of the left-right weak interaction model with parameters δ and ζ was investigated. It was shown that within this model, CP violation effects in the decays of K^0-mesons, D^0-mesons, B^0-mesons, and B_s^0-mesons can be successfully described. The results of calculations within the extended left-right model with parameters δ and ζ are confirmed by experimental results. Thus, the nature of CP violation is related to the presence of a right-handed vector boson admixture.

The analysis of the latest most accurate experimental data on neutron decay for the possibility of the existence of the right-handed vector boson W_R is carried out. As a result of the analysis, it is found that there is an indication of the existence of the right-handed vector boson W_R with a mass of M_W_R≈ 319_ - 20^ + 26 GeV and a mixing angle with W_L : ζ = –0.034 ± 0.013. This result should be considered, on the one hand, as a challenge to experimental physics at colliders, where the upper limit on the mass of the right-handed vector boson W_R is significantly higher and, on the other hand, as evidence that even more accurate measurements of neutron decay and its theoretical analysis are needed.

The analysis of the latest most accurate experimental data on neutron decay for the possibility of the existence of the right vector boson W R is carried out. As a result of the analysis within the framework of the left-right symmetric model, it was found that there is an indication of the existence of the right vector boson W R with a mass of M W R = 304 − 20 + 24 GeV , and a mixing angle with W L : ζ = − 0.039 ± 0.0 1 4 . It is shown that this result does not contradict the experiments at colliders to search for a hypothetical vector boson. In addition, it is shown that it is possible to describe the effects of C P violation in decays of neutral K -mesons and D -mesons using the parameters of the extended left-right symmetric model obtained from neutron decay, i.e., squared masses of the left and right bosons ratio and the mixing angle. The formation of baryon-lepton asymmetry of the Universe is considered within the framework of the left-right model of weak interaction with C P violation.

Software has been developed to simulate experiments with ultracold neutrons (UCN) at the PIK reactor (Gatchina, Russian Federation). Using this software, the neutron guide system was optimized, through which neutrons are supplied from the UCN source to the experimental installations. The calculations considered two options: with a straight neutron guide and a neutron guide with a downward bend. For a bent neutron guide, when separating membranes are placed at the bottom of the neutron guide, neutrons pass through them at increased velocity due to gravitational acceleration. Due to this, it is possible to reduce neutron losses. Monte Carlo calculations showed that in an experiment to search for the electric dipole moment of a neutron, an accuracy of 1 × 10–27 e cm/year can be obtained, and in an experiment to measure the neutron lifetime, the statistical uncertainty can be improved to 0.1 s.

According to the assumption that sterile neutrinos are right-handed neutrinos, an analysis of the current experimental situation in neutron decay for right-handed currents was carried out. As the result of the analysis, it was found that there is an indication of the existence of the right-handed vector boson W_R with a mass of M_W_R = 304_ - 22^ + 28 GeV and a mixing angle with W_L : ζ = - 0.038 ± 0.014 . It is shown that this result does not contradict experiments at colliders to search for the hypothetical vector boson. This circumstance is the basis for discussing the possibility of extending the Standard Model with an additional gauge vector boson W_R with small mixing with the left-handed vector boson W_L . In addition, there are grounds for considering the possibility of the existence of right-handed neutrinos. This circumstance is the basis for discussing the possibility of expanding the Standard Model with an additional gauge vector boson W_R and right-handed neutrinos. In this regard, the possibility of explaining dark matter in the Universe by right-handed neutrinos is analyzed. Various aspects of such an approach to the problem of dark matter are discussed: dynamics of dark matter formation and stability of dark matter consisting of right-handed neutrinos.

Neutrino-4 experiment observed the effect of neutrino oscillation to a sterile state with 3 standard deviation confedence level. With the aim of a significant increase in the accuracy of the experiment, a second neutrino laboratory is created on the SM-3 reactor (Dimitrovgrad, Russia). The Neutrino-4 collaboration will improve the detector in the first neutrino laboratory also. Equipment for the new neutrino laboratory at the SM-3 reactor is prepared and installation is in progress. Main part of the improvement is a new scintillator with higher gadolinium concentration and doped with DIN to increase pulse shape discrimination abilities. Improvements will allow to increase statistical accuracy of the experiment by 2.7 times and to achieve confidence level of the sterile neutrino observation up to 5σ .

A Monte Carlo model of an experiment with the universal trap of ultracold neutrons at the PIK reactor has been developed. The project assumes that in one installation two traps are installed on the same axis: material and magnetic. By rotating the trap system around an axis, it is possible to carry out gravitational capture of UCNs either into a material or into a magnetic trap. Thus, on one installation it is possible to compare the material and magnetic storage of UCNs under the same conditions. The motivation for such an experiment is the disagreement in the results of measuring the neutron lifetime in material and magnetic traps. As a result of the simulation, the sensitivity of the experiment at the PIK reactor was obtained.

When ultracold neutrons interact with moving surfaces, their energy can change (so-called turbine effect). In this case, both an increase and a decrease in the neutron energy are possible. In previous experiments with the capture of ultracold neutrons in a gravitational trap by rotating it, it was made to have the shape of a body of revolution, which was done specifically to avoid the turbine effect. In this paper, the authors consider an experiment with a rotating gravitational trap that does not have the shape of a body of revolution. The Monte Carlo method was used to simulate the turbine effect at different stages of the experiment. The transformation of the neutron spectrum over time is calculated as a function of the trap rotation speed. A possible systematic error in the measurement of the neutron lifetime due to the influence of the turbine effect is considered. Experimental parameters are obtained for which it is absent.

The paper proposes an experiment to measure the neutron lifetime by storing ultracold neutrons in a rotating magnetic trap. The magnetic trap is a set of NdFeB permanent magnets. By rotating the trap around a horizontal axis, it is possible to carry out the gravitational capture of ultracold neutrons and their holding. A design option is presented when two traps are located in one installation on the same axis: material and magnetic. The sensitivity of the magnetic trap is assessed in comparison with the material one under equal measurement conditions. One of the factors influencing the systematic error of the experiment will be the process of neutron depolarization in a magnetic field. Therefore, the paper considers the issue of developing a magnetic system that minimizes the probability of neutron depolarization. The so-called turbine effect is also considered, which can manifest itself in a change in the energy of ultracold neutrons during rotation due to interaction with the flat faces of the trap. The proposed gravitational capture of ultracold neutrons in a magnetic trap is a fundamentally new approach that has never been implemented before. The experiment can be carried out on the ultracold neutron source under construction at the PIK reactor.

An experiment is being developed to determine the λ value (the ratio of the axial weak interaction constant GA to the vector constant GV) by a simultaneous measurement of electron (A) and neutrino (B) β‑decay asymmetries using the same setup. The λ measurement is based on the ratio: λ = (A – B)/(A + B). The simultaneous measurement of A and B on the same setup is recommended to be carried out using ultracold neutrons stored in the magnetic field of a superconducting solenoid. The proposed method for determining λ, firstly, makes it possible to disregard the contribution of the Fierz interference term, and, secondly, eliminates the necessity of accurate measurement of the neutron polarization. The presented method allows one to measure the λ value with an accuracy of 10–4.

An experiment aimed at searching for a sterile neutrino using a new detector of the second neutrino laboratory at the SM-3 reactor (Dimitrovgrad, Russia) has been simulated. This detector is a scintillation detector of reactor antineutrinos with a multisection structure and horizontal arrangement of sections. Distributions of counts from prompt and delayed signals, as well as the dependence of detector efficiency on the selected thresholds, have been obtained by simulation. The antineutrino flux has been simulated with an allowance for the dimensions of the reactor core and its spatial location with respect to the detector. This simulation has been used as a basis to calculate the effect that should be obtained by measurements for the specified parameters of oscillations and energy resolution of the detector.

In the experiment "Neutrino-4" on the search for a sterile neutrino, the effect of oscillations was found at a confidence level of 3 standard deviations. In order to significantly increase the accuracy of the experiment, a second neutrino laboratory is created at the SM-3 reactor (Dimitrovgrad, Russia) and a new neutrino detector is developed. The scintillation-type detector consists of 4 modules having a multi-sectional structure with a horizontal arrangement of 100 sections with PMTs located on both sides of the section. The possibility of increasing the accuracy of the experiment by a factor of 2.7 is shown, which will make it possible to achieve a confidence level of more than 5 standard deviations and answer the question of the existence of a sterile neutrino.

In the experiment "Neutrino-4" on the search for a sterile neutrino, the effect of oscillations was found at a confidence level of 3 standard deviations. In order to significantly increase the accuracy of the experiment, a second neutrino laboratory is created at the SM-3 reactor (Dimitrovgrad, Russia) and a new neutrino detector is developed. The scintillation-type detector consists of 4 modules having a multi-sectional structure with a horizontal arrangement of 100 sections with PMTs located on both sides of the section. The possibility of increasing the accuracy of the experiment by a factor of 2.7 is shown, which will make it possible to achieve a confidence level of more than 5 standard deviations and answer the question of the existence of a sterile neutrino. Keywords: sterile neutrino, reactor antineutrino.

The PIK reactor at NRC "Kurchatov Institute"-PNPI is going to be equipped with a high-flux Ultra Cold Neutron (UCN) source for fundamental physics researches. The UCN source will use superfluid helium, which will make possible to achieve the density of UCN 2.2·10^3 cm-3, that has not yet been achieved anywhere in the world. The UCN source will be installed on the GEK-4 channel, which will make possible to obtain a low value of heat influx to cryogenic vessels from reactor radiation. The heat removal from the UCN source vessel will be implemented by using a heat exchanger. The calculated UCN density in the EDM spectrometer chamber at the PIK is going to be 200 cm-3, which is 20 times higher than the existing UCN densities in the world. For a new UCN source based on superfluid helium, an extensive research program has been developed in field of the physics of fundamental interactions, including the search for a nonzero neutron EDM, precision measurement of the neutron lifetime, and search for mirror dark matter. Keywords: ultracold neutrons, neutron sources, superfluid helium, neutron EDM, neutron decay.

In view of the possibility of the existence of a sterile neutrino, test measurements of the dependence of the reactor antineutrino flux on the distance from the reactor core has been performed on SM-2 reactor with the Neutrino-2 detector model in the range of 6–11 m. Prospects of the search for reactor antineutrinos at short distances have been discussed.