Vol 74, No 2 (2019)

The results of search for new decays of beauty baryons in the LHCb experiment are presented. In particular the new decays Λ_b⁰→ψ(2S)pπ⁻, \({\rm{\Lambda }}_b^0 \to {\rm{\Lambda }}_c^ + p\overline p {\pi ^ - }\), Λ_b⁰→pK⁻π⁺π⁻, Λ_b⁰→pK⁻K⁺K⁻, Ξ_b⁰ → pK⁻π⁺π⁻, Ξ_b⁰ → pK⁻π⁺K⁻ are observed and ratios of branching fractions are measured. The results are based on the proton-proton collisions data collected by the LHCb experiment at the Large Hadron Collider.

This paper considers the problem of optimal integration of the components of the global network of laser gravitational-wave antennas in order to improve the detection efficiency and to better estimate the parameters of astrophysical gravitational-wave signals. A quasi-harmonic burst (chirp) that accompanies the merger of a relativistic binary star at the end of its evolution has been selected as a signal. The shape of such a signal is known up to a set of parameters to be estimated against the background of large coherent and stochastic noise. An alternative possibility of taking into account the coherent excitation phase of individual detectors (component integration by input) is analyzed in addition to the well-known method for filtering output signals by coincidence in time (component integration by output). Statistical detection characteristics for both modes are calculated. The method typical for problems of distinguishing deterministic signals in radar systems is used. A significant increase in detection efficiency during the input integration of network components is shown.

In this work, the free energy and the equation of state of a system of solid spheres in narrow cylindrical pores are determined using the combined method of accelerated convergence of series. This method includes the Euler method and a method based on taking the behavior of the system into account at high densities near the dense packing and on the idea of the effective number of the nearest neighbors. The results are compared with the data of a computer experiment for three different values of pore size and in all cases good agreement between theory and experiment was obtained. These are much better than the results of virial expansion, and when the transverse pore sizes increase, better than the results found on the basis of a series in powers of pressure as well. The method makes it possible to estimate the limits of applicability of the method of convergence acceleration, based on the transition from a series in density to a series in terms of pressure. To do this, the density with close packing and the maximum allowable density found by the method of Euler are compared. If these densities are close, then only the Euler method can be used. In the case of a significant difference, a combined method of accelerated convergence is required.

The analysis of the available data on the α + ⁹Be elastic scattering in the energy range from 28 to 104 MeV, including recent measurements at energies of 30, 40, and 90 MeV is carried out. The parameters of the semi-microscopic potential are obtained in the framework of the dispersion optical model, in which the exchange components of the average field potential were calculated using the previously proposed pseudo-oscillator approximation for the single-particle density matrix. The found potential is tested using the distorted wave method on the analysis of inelastic scattering in the considered energy region with excitation of the 5/2⁻ (2.43 MeV) and 7/2⁻ (6.38 MeV) levels of the ground-state rotational band. The potential parameters used for the output channel were estimated on the basis of the energy dependence. A satisfactory description of the angular distributions and the values of the deformation length is obtained.

In this article a model for calculating energy and particles densities is presented in order to control burning plasma in the case of D³He fuel in spherical tokamak (ST). A spherical tokamak is a possible candidate for a D³He fusion reactor due to its high-beta value. In this model a one-dimensional approximation of the transport equation for energy as well as the density of deuterium-helium3 fuel ions and alpha particles is represented in cylindrical coordinates by a system of partial differential equation. By applying these simulation equations to control particles and energy densities profiles, the system is discretized in space using a finite difference method and a back-stepping design for D³He aneutronic fuel in tokamaks. Results obtained for boundary control conditions shows that initial values are approaching to equilibrium profiles and also the system achieves the stable equilibrium. It is also seen that with the controller modulation of the alpha particles, deuterium-helium3 and energy densities at the edge of the plasma, they are approaching to stable equilibrium points. The results of boundary control law show that the profiles can be successfully controlled with just one step of back-stepping.

Generation of terahertz radiation upon filamentation in air of two-color radiation in loose focusing conditions with focal lengths from 30 to 312 cm and a beam diameter of 0.8 cm was studied. Two-color radiation was generated in a nonlinear BBO crystal irradiated by a converging laser beam. Measurements show that the energy input into the medium increases dramatically with a decrease in the focal length to 50 cm or less; at F = 30 cm, the energy of a terahertz pulse linearly depends on the laser pulse energy and increases significantly at F = 50 cm. Terahertz radiation is still not observed at longer focal lengths, which is apparently due to a spatio—temporal mismatch of the radiation of the first and second harmonics.

Here we present CMOS compatible fabrication methods and the results of an experimental study of single-atom single-electron transistors made from silicon on insulator and based on various dopant atoms. Transistors with channels doped with arsenic (As), phosphorus (P), gold (Au) and potassium (K) atoms were fabricated and studied. Two methods for fabricating of experimental transistor structures are presented. The first method (As, P transistors) used a inhomogeneously doped in depth silicon layer and controlled reduction of the size of the transistor channel in several cycles of isotropic reactive-ion etching. The second method (Au and K transistors) used an undoped silicon layer and the subsequent implantation of dopant atoms into a preformed transistor channel. Dopant electron and hole levels of Au and K atoms in silicon are located near the middle of the silicon band gap, which provides a small effective size of the dopant charge center and, as a result, a high value of the charge energy and operating temperature of the transistor compared to the traditional dopants (P, As, Sb, B). The values of the charge energy of the Au and K transistors, which were estimated from the measurements (Ec ≥ 150 meV), are much higher than those of the As and P transistors (Ec < 30 meV). Important advantages of the proposed methods are: controlled implantation of various impurities and possibility to combine etching and implantation cycles during sample preparation.

Employing the nonequilibrium Green’s function technique, electron transport characteristics through a laterally coupled triple-quantum-dot chain are investigated. The conductance versus electron energy is numerically calculated. Two anti-resonance points change into two anti-resonance bands with increasing the size of triple-quantum-dot chain. The widths of two anti-resonance bands are the same and can be regulated via adjusting the inter-dot tunneling coupling strength in the main chain or its attachment. Spin-polarized window emerges due to Zeeman splitting as an external magnetic flux is introduced. Our studies demonstrate that the system can be used as a quantum switch or an efficient spin filtering.

Using the equivariant catastrophe theory, we classify phenomenological models of phase transitions with a three-component order parameter and with a number of control parameters from one to four. The analysis of phase diagrams of the obtained models shows that the description of all low-symmetry phases requires fewer terms of the power-series expansion than that required by the model constructed using the traditional method taking all terms up to the 2nth power into account (n > 1). The theoretical temperature dependence of the heat capacity is compared with the experimental data in the GaV₄S₈ compound.

The objective of this study is to introduce novel fundaments to characterize and assess the material behaviors on photon beam attenuation and beam softening for high filtration system quality. This study was done by Monte Carlo method using BEAMnrc code and BEAMDP code. After validation of Monte Carlo model of linear accelerator with flattening filter; the later was replaced by material slab of aluminum and copper with different thickness. The photon beam attenuation was evaluated for primary photon fluence and secondary photon fluence for checking the dependence on energy; the beam softening was also evaluated based on beam attenuation coefficients. Based on the beam softening coefficients that were correlated by attenuation coefficients, the softening index was introduced as a new parameter to assess the material effects for high filtration system quality. These novel fundaments allow assessing the quality of a material for high photon beam filtration system quality.

The advancement of space technology opens new perspectives in developing high-resolution models of the Earth’s gravitational field. The use of a precision laser interferometric system requires taking relativistic effects in the inter-satellite ranging within the satellite constellation into account. The main quantity measured by the laser system is the phase incursion of the laser beam when passing a double one-way range between the satellites. A solution for the relativistic phase is obtained that considers not only the usual Shapiro term but also the contribution of the quadrupole term to distributions of the Earth’s mass, the Earth’s spin, and tidal gravitational fields caused by the gravitational potentials of the outer bodies of the Solar System. Relativistic reduction terms are estimated at the accuracy level of ∼1 nm, which fully satisfies the accuracy of precision measurements in the two-spacecraft formation. It will be necessary to take the relativistic effects of the next order of smallness into account in the next-generation gravitational twin missions.

The Slichter mode (₁S₁) is the longest-period mode of Earth’s free oscillations. The period of this mode depends on the difference between the densities of the outer liquid and inner solid cores, thus making its detection very important for the refinement of models of the Earth. Despite numerous attempts at detecting this mode with the use of a network of superconducting gravimeters, there currently is no confirmed experimental data on the observation of the Slichter mode due to its small amplitude on the surface. In this work, it is proposed to detect the Slichter mode using the data from the laser interferometer-strainmeter of the Sternberg State Astronomical Institute of the Moscow State University (Northern Caucasus) with a measuring arm length of 75 m. For this purpose, an asymptotically optimal algorithm was developed for the analysis of data with consideration for their statistical properties, and the processing of synthetic data was modeled to estimate the magnitude of the possible observed effect and the detection indicators.