arXiv subjects
Publications and source records attributed to O. M. Zherebtsov.
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).
We analyse a change of a deficit of reactor antineutrinos at distances smaller than 100 m by changing the lifetime of the neutron from tau_n = 885.7 s to tau_n = 879.6 s, calculated for the axial coupling constants lambda = - 1.2694 and lambda = - 1.2750, respectively, in order to get a result corresponding the new world average value tau_n = 880.1(1.1) s. We calculate the angular distribution and cross section for the inverse beta-decay, taking into account the contributions of the "weak magnetism" and the neutron recoil to next-to-leading order in the large baryon mass expansion and the radiative corrections of order alpha/π~ 10^(-3), calculated to leading order in the large baryon mass expansion. We obtain an increase of a deficit of reactor antineutrinos in of about 0.734%.
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.
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.
The accumulation of dark matter near the Earth is considered. We analyze the case of long range interaction forces. Additional density of the dark matter at the Earth's surface is calculated. We show that this density exceeds the mean density of the dark matter in our galaxy by more then $10^5$ times for some values of dark matter particle mass. Accumulation of WIMP's near the Earth by the same mechanism is also analyzed.
A method of using a gravitational UCN spectrometer to search for long-range forces between neutrons and atoms is proposed. The constraints on the strength of long-range forces within the range of 10-10 - 10-4 cm can be obtained from the experiments on measurements of the total cross section of interaction of UCN with atoms of the noble gases (He, Ne, Ar, Kr) and the data on the coherent neutron scattering length of the nucleus. The first result of such an analysis is presented. Further prospect of UCN method is discussed.
The possibility of using a trap with ultracold neutrons as a detector of dark matter particles with long-range forces is considered. The basic advantage of the proposed method lies in possibility of detecting the recoil energy 10-7 eV. The restrictions on parameters of Yukawa type interaction potential between dark matter particles and a neutron are presented for different dark matter densities on the Earth. The assumption concerned with long-range interaction of dark matter particles and ordinary matter leads to a substantial enhancement of cross section at low energy. Consequently, there arises a possibility of capture and accumulation of dark matter in a gravitational field of the Earth. Rough estimation of accumulation of low-energy dark matter on the Earth is discussed. The first experimental restrictions for existence of dark matter with long-range forces on the Earth are presented.
The search for CP violating forces between nucleons in the so-called axion window of force ranges lam between 2x10^-5 m and 0.02 m is interesting because only little experimental information is available there. Axion-like particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product gs x gp of scalar and pseudo-scalar dimensionless constants, as a function of the force range lam, gs x gp x lam^2 <= 2x10-21 [cm^2] (C.L.95%) for 10^-4 cm < lam < 1 cm. For 0.1 cm < lam < 1 cm previous limits are improved by 4 to 5 orders of magnitude.
Mirror matter is considered as a candidate for dark matter. In connection with this an experimental search for neutron - mirror neutron (nn') transitions has been carried out using storage of ultracold neutrons in a trap with different magnetic fields. As a result, a new limit for the neutron - mirror neutron oscillation time has been obtained, tau_osc >= 448 s (90% C.L.), assuming that there is no mirror magnetic field larger than 100 nT. Besides a first attempt to obtain some restriction for mirror magnetic field has been done.
Our experiment using gravitationally trapped ultracold neutrons (UCN) to measure the neutron lifetime is reviewed. Ultracold neutrons were trapped in a material bottle covered with perfluoropolyether. The neutron lifetime was deduced from comparison of UCN losses in the traps with different surface-to-volume ratios. The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. In this experiment, the UCN storage time is brought closer to the neutron lifetime than in any experiments before:the probability of UCN losses from the trap was only 1% of that for neutron beta decay. The neutron lifetime obtained,878.5+/-0.7stat+/-0.3sys s, is the most accurate experimental measurement to date.
The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter. Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n' with oscillation time much smaller than the neutron lifetime. A dedicated search for vacuum transitions n->n' has to be performed at weak magnetic field, where both states are degenerate. We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions. We obtain a new limit for the oscillation time of n-n' transitions, tau_osc (90% C.L.) > 414 s. The corresponding limit for the mixing energy of the normal and mirror neutron states is delta_m (90% C.L.) < 1.5x10-18 eV.
The author of article discusses the possible systematic effects in our experiment using reference and picture from allegedly our publication. First of all this publication does not exist. The assumption of author about the probability of lower energy upscattering is in a rough contradiction (300 times) with our experimental limit which is extremely lower, about 6x10-9 per neutron collision. The second assumption of author concerning quasi-stable orbits of UCN with higher energy due to specular neutron reflection from trap wall is also in a rough contradiction with our experimental data clear demonstrated in our previous articles as well in the last very detailed article recently presented in the arXiv. We are very surprised that author discusses well known questions studied in our experiment in details.
Accurate calculations of the binding energies, the hyperfine splitting, the bound-electron g-factor, and the parity nonconservation effects in heavy few-electron ions are considered. The calculations include the relativistic, quantum electrodynamic (QED), electron-correlation, and nuclear effects. The theoretical results are compared with available experimental data. A special attention is focused on tests of QED in a strong Coulomb field.
The ground state hyperfine splitting values and the transition probabilities between the hyperfine structure components of high Z lithiumlike ions are calculated in the range $Z=49-83$. The relativistic, nuclear, QED and interelectronic interaction corrections are taken into account. It is found that the Bohr-Weisskopf effect can be eliminated in a combination of the hyperfine splitting values of the hydrogenlike and lithiumlike ions of an isotope. This gives a possibility for testing the QED effects in a combination of the strong electric and magnetic fields of the heavy nucleus. Using the experimental result for the $1s$ hyperfine splitting in ^{209}Bi^{82+}, the 2s hyperfine splitting in ^{209}Bi^{80+} is calculated to be ΔE=0.7969(2) eV.