arXiv subjects

A. K. Fomin

Publications and source records attributed to A. K. Fomin.

At least 19 recordsLinked to original sources

arXiv2026

Precision studies of neutron decay, left-right asymmetry model of weak interaction, CP-violation and baryon asymmetry of the Universe

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$\pm$0.9)$\cdot$10$^{-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$\pm$60) GeV is given by the relation: from the parameter $δ$=(5.5$\pm$1.8)$\cdot$10$^{-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 $\pmπ$/2, which corresponds to 100% CP violation. The results of calculations within the left-right asymmetry model with parameters $δ$ and $ζ$ are confirmed by experimental results with neutral mesons. The formation of baryon asymmetry in the Universe is considered in a left-right asymmetry model of weak interaction with an admixture of a right vector boson with different signs of the mixing angle with $W^-$ and $W^+$.

hep-ph↗

arXiv2026

CP-violation effects in neutral meson oscillations in the left-right weak interaction model

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 $ζ= -0.039\pm0.014$ with the left vector boson $W_L$ and a ratio of the squares of the masses of $W_1$ and $W_2$ equal to $δ= 0.070\pm0.010$. 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.

hep-ph↗

arXiv2025

Analysis of experimental data on neutron decay for the possibility of the existence of the right vector boson $W_R$

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 $M_{W_R}=304_{-20}^{+24} \text{GeV}$, and a mixing angle with $W_L: ζ= -0.039\pm 0.014$. 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 CP violation in decays of neutral $K$-mesons, $D$-mesons and $B_s^0$ 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 CP violation. A new experimental design for measuring neutron decay asymmetries with increased accuracy is presented.

hep-ph↗

arXiv2021

Experiment Neutrino-4 search for sterile neutrino and results of measurements

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 $Δm_{14}^2$ and $\sin^22θ_{14}$. 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 $2.9σ$ level with parameters $Δm_{14}^2=(7.3\pm0.13_{st}\pm1.16_{sys})\text{eV}^2 = (7.3\pm1.17)\text{eV}^2$ and $\sin^22θ_{14}= 0.36\pm0.12_{stat}(2.9σ)$. Monte Carlo based statistical analysis gave estimation of confidence level at $2.7σ$. 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.

hep-ex↗

arXiv2020

The first observation of effect of oscillation in Neutrino-4 experiment on search for sterile neutrino (continuation)

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 $42\times42\times35\textrm{cm}^3$ 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 $Δm^2_{14}$ and $\sin^2 2θ_{14}$. 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 $3.5σ$ in the vicinity of $Δm^2_{14} \approx 7.26\textrm{eV}^2$ and $\sin^2 2θ_{14} \approx 0.38$. Combining the result of the Neutrino-4 experiment and the result of the gallium anomaly effect we obtained value $\sin^2 2θ_{14} \approx 0.35 \pm 0.07 (5σ)$. 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 $\sin^2 2θ_{14} \approx 0.35 \pm 0.07 (5σ)$ and $Δm^2_{14} \approx (7.3 \pm 0.7)\textrm{eV}^2$ allow make assessment on the mass of a neutrino: $m_β \approx 0.8\textrm{eV}$.

hep-ex↗

arXiv2018

Experiment Neutrino-4 and restrictions for sterile neutrino

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 $Δm^2_{14}$ and $\sin^2(2θ)$ limitations. Result of this analysis is exclusion of reactor and gallium anomalies area with 95% CL. Experiment future perspectives are discussed.

physics.ins-det↗

arXiv2017

Neutron lifetime measurements with the big gravitational trap for ultracold neutrons

Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. There remains the unsolved problem of a 3.9σ discrepancy between measurements of this lifetime using neutrons in beams and those with stored neutrons (UCN). In our experiment we measure the lifetime of neutrons trapped by Earth's gravity in an open-topped vessel. Two configurations of the trap geometry are used to change the mean frequency of UCN collisions with the surfaces - this is achieved by plunging an additional surface into the trap without breaking the vacuum. The trap walls are coated with a hydrogen-less fluorine-containing polymer to reduce losses of UCN. The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. At 80 K, the probability of UCN loss due to collisions with the trap walls is just 1.5% of the probability of beta-decay. The free neutron lifetime is determined by extrapolation to an infinitely large trap with zero collision frequency. The result of these measurements is 881.5 +/- 0.7_stat +/- 0.6_syst s which is consistent with the conventional value of 880.2 +/- 1.0 s presented by the Particle Data Group. Future prospects for this experiment are in further cooling to 10 K which will lead to an improved accuracy of measurement. In conclusion we present an analysis of currently-available data on various measurements of the neutron lifetime.

nucl-ex↗

arXiv2017

Experiment NEUTRINO-4 Search for Sterile Neutrino

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.

physics.ins-det↗

arXiv2016

Neutrino-4 experiment on search for sterile neutrino with multi-section model of detector

In order to carry out research in the field of possible existence of sterile neutrino the laboratory based on SM-3 reactor (Dimitrovgrad, Russia) was created to search for oscillations of reactor antineutrino. The prototype of a multi-section neutrino detector with liquid scintillator volume of 350 l was installed in the middle of 2015. It is a moveable inside the passive shielding detector, which can be set at distance range from 6 to 11 meters from the reactor core. Measurements of antineutrino flux at such small distances from the reactor core carried out with movable detector for the first time. The measurements carried out with detector prototype demonstrated a possibility of measuring a reactor antineutrino flux in difficult conditions of cosmic background at Earth surface.

physics.ins-det↗

arXiv2015

Creation of a neutrino laboratory for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6-11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.

physics.ins-det↗

arXiv2014

New measurements of neutron electric dipole moment with double chamber EDM spectrometer

The article presents results on neutron electric dipole moment measurements (EDM), made by ILL reactor using PNPI experimental installation. Double chamber magnetic resonance spectrometer with prolonged holding of ultra cold neutrons has been employed. The obtained results at 90% confidence level determine the upper limit for EDM neutron quantity equal to $|d_n| < 5.5 \cdot 10^{-26}$ e$ \cdot$cm.

nucl-ex↗

arXiv2014

On possibility of realization NEUTRINO-4 experiment on search for oscillations of the reactor antineutrino into a sterile state

One has investigated possibility of performing NEUTRINO-4 experiment on search for reactor neutrino oscillations into a sterile state at research reactors. The simulated experiment has been conducted at 16 MW reactor WWR-M in PNPI with the purpose of implementing a full scale experiment with the help of 100 MW reactor SM-3 in RIAR. Background conditions for making such an experiment have been examined at both reactors. The conclusion has been made on possible implementation of a full scale experiment NEUTRINO-4 at the reactor SM-3 in RIAR.

physics.ins-det↗

arXiv2013

New measurements of neutron electric dipole moment

We report a new measurement of the neutron electric dipole moment with the PNPI EDM spectrometer using the ultracold neutron source PF2 at the research reactor of the ILL. Its first results can be interpreted as a limit on the neutron EDM of $|d_{\rm n}| < 5.5 \times 10^{-26} \rm{e} \cdot \rm{cm}$ (90% confidence level).

nucl-ex↗

arXiv2013

"Neutrino-4" experiment: preparations for search for sterile neutrino at 100 MW reactor SM-3 at 6-13 meters

There has been designed an experimental project "Neutrino-4" for 100 MW reactor SM-3 to test the hypothesis of the "reactor antineutrino anomaly". Advantages of the reactor SM-3 for such an experiment are low background conditions as well as small dimensions of a reactor core - 35x42x42 cm3. One has carried on the Monte-Carlo modeling of a position sensitive antineutrino detector consisting of 5 operation sections, which as a result of displacement, covers the distance from 6 to 13 meters from the reactor core. One has succeeded in obtaining an experimental area of sensitivity to oscillation parameters, which enables to verify the hypothesis of reactor antineutrino oscillations into a sterile state.

hep-ph↗

arXiv2012

Ultra cold neutron trap as a tool to search for dark matter with long-range radius of forces

The problem of possible application of an ultracold neutron (UCN) trap as a detector of dark matter particles with long-range radius of forces has been considered. Transmission of small recoil energy in scattering is a characteristic of long-range forces. The main advantage of the ultracold neutron technique lies in possibility of detecting recoil energy as small as $10^{-7}$ eV. Here are presented constraints on the interaction potential parameters: $U(r)=a r^{-1} e^{-r/λ}$ for dark matter particles and neutrons, as well as on the density value of long-range dark matter on the Earth. The possible mechanism of accumulation of long-range dark matter on the Earth surface is considered and the factor of density increase on the Earth surface is evaluated. The results of the first experiment on search of astronomical day variation of ultracold neutron storage time are under discussion.

nucl-ex↗

arXiv2011

New evaluation of neutron lifetime from UCN storage experiments and beam experiments

The analysis of experiments on measuring neutron lifetime has been made. The latest most accurate result of measuring neutron lifetime [Phys. Lett. B 605, 72 (2005)] 878.5 \pm 0.8 s differs from the world average value [Phys. Lett. B 667, 1 (2008)] 885.7 \pm 0.8 s by 6.5 standard deviations. In view of this both the analysis and the Monte Carlo simulation of experiments [Phys. Lett. B 483, 15 (2000)] and [Phys. Rev. Lett. 63, 593 (1989)] have been performed. Systematic errors about -6 s have been found in both experiments. The table of results of neutron lifetime measurements is given after corrections and additions have been made. A new world average value of neutron lifetime makes up 880.0 \pm 0.9 s. Here is also presented a separate analysis of experiments on measuring neutron lifetime with UCN and experiments on the beams. The average neutron lifetime for experiments with UCN is equal to 879.3(0.6) s, while for experiments on the beams it is equal to 889.1(2.9) s. The present difference of average values for both groups is (3.3 sigma) and needs consideration. The contribution of beam experiments into the world average value is not high, therefore it does not influence the above analysis. However, it is an independent problem to be solved. It seems desirable that the precision of beam experiments should be enhanced.

nucl-ex↗

arXiv2010

A New World Average Value for the Neutron Lifetime

The analysis of the data on measurements of the neutron lifetime is presented. A new most accurate result of the measurement of neutron lifetime [Phys. Lett. B 605 (2005) 72] 878.5 +/- 0.8 s differs from the world average value [Phys. Lett. B 667 (2008) 1] 885.7 +/- 0.8 s by 6.5 standard deviations. In this connection the analysis and Monte Carlo simulation of experiments [Phys. Lett. B 483 (2000) 15] and [Phys. Rev. Lett. 63 (1989) 593] is carried out. Systematic errors of about -6 s are found in each of the experiments. The summary table for the neutron lifetime measurements after corrections and additions is given. A new world average value for the neutron lifetime 879.9 +/- 0.9 s is presented.

nucl-ex↗

arXiv2010

A Detailed Analysis and Monte Carlo Simulation of the Neutron Lifetime Experiment S. Arzumanov et al., Phys. Lett. B 483 (2000) 15

We performed a detailed analysis and the Monte Carlo simulation of the neutron lifetime experiment [S. Arzumanov et al., Phys. Lett. B 483 (2000) 15] because of the strong disagreement by 5.6 standard deviations between the results of this experiment and our experiment [A. Serebrov et al., Phys. Lett. B 605 (2005) 72]. We found a few effects which were not taken into account in the experiment [S. Arzumanov et al., Phys. Lett. B 483 (2000) 15]. The possible correction is -5.5 s with uncertainty of 2.4 s which comes from initial data knowledge. We assume that after taking into account this correction the result of work [S. Arzumanov et al., Phys. Lett. B 483 (2000) 15] for neutron lifetime 885.4 +/- 0.9stat +/- 0.4syst s could be corrected to 879.9 +/- 0.9stat +/- 2.4syst s.

nucl-ex↗