Bose-Einstein correlations of pion wavepackets

A wavepacket model for a system of free pions, which takes into account the full permutation symmetry of the wavefunction and which is suitable for any phase space parametrization is developed. The properties of the resulting mixed ensembles and the two-particle correlation function are discussed. A physical interpretation of the chaoticity λ as localization of the pions in the source is presented. Two techniques to generate test-particles, which satisfy the probability densities of the wavepacket state, are studied:

1. A Monte Carlo procedure in momentum space based on the standard Metropolis technique.
2. A molecular dynamic procedure using Bohm’s quantum theory of motion. In order to reduce the numerical complexity, the separation of the wavefunction into momentum space clusters is discussed. In this context the influence of an unauthorized factorization of the state, i. e. the omission of interference terms, is investigated. It is shown that the correlation radius remains almost uneffected, but the chaoticity parameter decreases substantially. A similar effect is observed in systems with high multiplicities, where the omission of higher order corrections in the analysis of two-particle correlations causes a reduction of the chaoticity and the radius. The approximative treatment of the Coulomb interaction between pions and the source is investigated. The results suggest that Coulomb effects on the correlation radii are not symmetric for pion pairs of different charges. For (π^?,π^?) pairs the radius, integrated over the whole momentum spectrum, increases substantially, while for (π⁺,π⁺) pairs the radius remains almost unchanged.

     

The influence of final state interaction on two-particle correlations in multiple production of particles and resonances

The structure of pair correlations of interacting particle moving with nearby velocities is analysed. A general formalism of the two-particle space-time density matrix, taking into account the space-time coherence of the production process, is developed. The influence of strong final state interaction on two-particle correlations in the case of the production of a systemresonance+particle is investigated in detail. It is shown that in the limit of small distances between the resonance and particle production points the effect of final state interaction is enhanced due to logarithmic singularity of the triangle diagram. Numerical estimates indicate that, in this limit, the effect of strong final state interaction becomes important even for two-pion correlations.     

Effect of convection and heat conduction on the laser gain in a nonequilibrium recombinational hydrogen wall plasma

The effect of a conducting body with a large heat capacity on the thermal state of a hydrogen plasma in the boundary surface layer is analyzed. It is shown that, under certain conditions, the energy accumulated in the plasma within the boundary layer can be efficiently transferred to the conducting body; this leads to plasma overcooling. The mathematical model of plasma incorporates mechanisms for convective heat exchange and heat conduction. The possibility is analyzed of the existence of nonequilibrium recombination states with inverse population in the overcooled wall plasma. It is shown that the maximum gain (a few tenths of cm^?1) on hydrogen nuclei is achieved at the 3-2 transition for the following initial parameters: the plasma pressure is 1–3 atm, the plasma temperature is 0.5 eV, the tungsten surface temperature is 300 K, and the body radius is 0.5–1.0 m.     

On calculating the oscillations of a viscous liquid layer over a solid spherical core in terms of the boundary layer theory

The theory of a boundary layer near the periodically oscillating free surface of a spherical viscous liquid layer over a solid core (bottom) is modified. Two boundary layers are considered to adequately describe a liquid viscous flow in the system: one at the free surface of the liquid and the other at the solid bottom. The thicknesses of the boundary layers are estimated, which provide any given discrepancy between an exact solution to the model problem and a solution obtained in the small viscosity approximation. Taking into account the boundary layer near the solid bottom is shown to be significant only for lower oscillation modes. For higher modes, the flow near the core can be considered potential. In the case of lower modes and shallow liquid, the surface and bottom boundary layers overlap and an eddy flow occupies the entire volume of the liquid.     

Distribution functions of a slightly nonideal multicomponent plasma

A regular perturbation theory technique is constructed using the plasma parameters of the equilibrium Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) equation chain for a multicomponent plasma in which higher order terms are small at all admissable interparticle distances, in contrast to the Debye equations. As a result, two correlation radii appear in a charge-asymmetric plasma: the Debye radius D and 2 D. The divergence of correlation functions characteristic of Debye splitting is eliminated in any order of the perturbation theory. For the proposed theory to be applicable the plasma parameter must be limited more severely, the deeper the depth of the potential well which appears upon approach of oppositely charged ions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–58, May, 1988.     

Asymptotic analysis of Bloch-Floquet waves in a thin bi-material strip with a periodic array of finite-length cracks

We present an asymptotic algorithm to solve a problem of wave propagation in a thin bi-material strip with an array of cracks situated at the interface between two materials. For small frequencies we construct an asymptotic solution which takes into account the singular behavior near the crack tips and the smooth nature of the oscillation far away from them. We construct the boundary layer solutions near the crack tips. The boundary layers are harmonic solutions in scaled domains. Dispersion equations are derived and solved within the frame of the asymptotic model.     

Asymptotic analysis of Bloch–Floquet waves in a thin bi-material strip with a periodic array of finite-length cracks

We present an asymptotic algorithm to solve a problem of wave propagation in a thin bi-material strip with an array of cracks situated at the interface between two materials. For small frequencies we construct an asymptotic solution which takes into account the singular behavior near the crack tips and the smooth nature of the oscillation far away from them. We construct the boundary layer solutions near the crack tips. The boundary layers are harmonic solutions in scaled domains. Dispersion equations are derived and solved within the frame of the asymptotic model.     

Underlying event background in two-pion correlations in p + p Collisions at √<Emphasis Type="Italic">s</Emphasis> = 0.9 and 7 TeV

When analyzing two-particle correlations for identical pions in p + p collisions at √s = 0.9 and 7 TeV, significant background correlation structures are observed. The structures are also observed for pairs of non-identical pions and are reproduced by Monte-Carlo simulations. We analyze these structures quantitatively and propose methods to account for their impact on the system sizes extracted from the fits to the identical pion correlation functions.     

Bose-Einstein correlations of neutral gauge bosons in pp collisions

The theory for Bose-Einstein correlations in case of neutral gauge bosons in pp collisions at high energies is presented. Based on quantum field theory at finite temperature, the two-particle Bose-Einstein correlations of neutral gauge bosons are carried out for the first time. As a result, the important parameters of the correlation functions can be obtained for the Z ⁰ Z ⁰ pairs. The article is published in the original.     

Beobachtungen von Diffusionsprozessen im Schichtensystem Silber-Zinksulfid mit dem Photoemissions-Elektronenmikroskop

By means of the photoemission electron microscope Balzers Metioscope KE 3 the diffusion processes were investigated which occur at elevated temperatures in a system of silver and zincsulfide coatings. At 150 °C the formation of Ag₂S at the surface of the silver film can be seen (high emitting round spots on bright background) and at 240 °C one can observe the diffusion of silver through the zincsulfide film (high emitting small spots on dark background). On heating coagulation process of the silver particles takes place in the boundary zone near the silver layer. With increasing temperatures the mobility of these particles becames high enough to allow them to migrate into the silver layer.     

The intensity of the field generated by a point source and reflected from a rough surface

This paper studies the intensity of the acoustic field generated by a point source above a rough surface with the Dirichlet or Neumann boundary conditions. The derived equations are valid for arbitrary distances between the source, receiver and rough surface, including the case when these distances are smaller than the correlation radius of the surface roughness. It is believed that the proposed method is an improvement of the more conventional approach, which is based on integration over individual areas of the rough surface and that is valid when the source, receiver, and surface are at large distances from each other. The main limitation in deriving the expressions for the acoustic field intensity is the condition that the mutual shadowing of the surface points is small, which is close to the small slope approximation for the rough surface profile. The derivation includes the limiting cases which lead to the traditional small perturbation method and Kirchhoff approximation.     

Effect of diffusion on nucleation of 2D and 3D nanoclusters in supersaturated solutions

The effect of diffusion on the steady-state nucleation of 2D and 3D nanoclusters is described analytically. Proposed approach takes self-consistently into account coupling between the kinetics of monomers near the cluster boundary, their diffusion and annihilation at other clusters. It has been shown that due to this coupling the nucleation barriers can considerably differ from those predicted by the thermodynamic approach.     

液3He中准粒子通过涡旋与固体表面之间的动量输运

本文对于与稀薄液³He-⁴He溶液相接触的振动固体表面的横声阻抗作了探讨。提出在液³He与基片之间有一准二维的超流液⁴He层的“三明治”模型,根据传输线理论得到表面阻抗与液³He的协强张量、超流⁴He层动量变化之间的关系式,推导出在“三明治”结构下量子涡旋的运动方程,并考虑涡旋运动与滑动边界条件计算了液³He中准粒子与固体表面之间的动量输运。从而由理论上 关键词：     

Quantum-statistical mechanics of a system of charged particles at high temperatures

If a quantum-mechanical potential is introduced the calculation of the quantummechanical binary distribution function for a system with Coulomb interaction is reduced to the well-known mathematical formalism of classical statistical mechanics in the case ofnλ³?1 (λ being the thermal wavelength). The two-particle quantummechanical potential is determined by the two-particle Slater sum. In this paper we calculated the two-particle Slater sum using an expansion according toe ² and the resolvent formalism. From the binary distribution function the correlation energy and the free energy as well were determined up to ordere ⁶. Symmetry effects were taken into account.     

Random Skew Plane Partitions and the Pearcey Process

We study random skew 3D partitions weighted by q ^vol and, specifically, the q → 1 asymptotics of local correlations near various points of the limit shape. We obtain sine-kernel asymptotics for correlations in the bulk of the disordered region, Airy kernel asymptotics near a general point of the frozen boundary, and a Pearcey kernel asymptotics near a cusp of the frozen boundary.     

Influence of dipole-dipole correlations on the stability of the biaxial nematic phase in the model bent-core liquid crystal

A molecular theory of biaxial nematic ordering in the system of bent-core molecules has been developed in the two-particle cluster approximation which enables one to take into account short-range polar correlations determined by both electrostatic dipole-dipole interaction and polar molecular shape. All orientational order parameters and short-range correlation functions are calculated numerically as functions of temperature in the uniaxial and in the biaxial nematic phases, and the results are compared with the ones obtained in the mean-field approximation and in the cluster approximation but without taking into consideration the dipole-dipole interaction. It is shown that short-range polar correlations and, in particular, the dipole-dipole correlations dramatically increase the temperature of the transition into the biaxial nematic phase and enhancing its stability range. The results are also very sensitive to the value of the opening angle of a model bent-core molecule.