Correlations between pions of low relative momenta

Two-particle pion correlations in exclusive πp and pp interactions at \(\sqrt s = 2.9 - 4\) GeV are studied in the region of low relative 4-momenta. Relevant correlation functions are obtained with allowance for the results of calculations based on the model of quark-gluon strings and the FRITIOF model. Positive correlations that make it possible to estimate the spatial size of the pion source are observed for pairs of identical pions. No correlations are observed for pairs featuring one charged and one neutral pion.     

Mechanism of oxygen response in carbon-based sensors

The mechanism of oxygen response in several newly synthesized oxygen-sensitive chars was studied with the use of EPR spectroscopy. The results suggest that the compounds contain two basic types of paramagnetic centers (PC). The change in oxygen concentration leads to a mutual and reversible transformation of PCs in chars, which is reflected in EPR parameters. The adsorbed molecular oxygen progressively disturbs the wave functions of the PCs and so breaks the Heisenberg exchange between them. At high oxygen concentration, the 2D dipole-dipole interaction between PCs at the surface comes into play and determines the EPR lineshape. A suggested model quantitatively describes the evolution of the basic EPR parameters of each PC as a function of oxygen concentration.     

Effect of preliminary oxidation annealing on properties of porous silicon impregnated with a tungsten-tellurite glass activated by Er and Yb

The effect of preliminary oxidation annealing of porous silicon (PS) on photoluminescence (PL) under laser pumping at wavelengths of 532 and 980 nm, EPR, and transverse current transport in structures based on PS with a fused tungsten-tellurium glass (TTG) doped with Er and Yb has been studied. It has been shown that such annealing and the presence of silicon nanocrystals (nc-Si) in PS promote multiple PL enhancement for both Er ions in TTG and nc-Si in PS at wavelengths of 750 and 1540 nm, respectively. As TTG is fused into PS, P _b -centers of nonradiative recombination are suppressed, while retaining discrete electron tunneling through nc-Si grains in PS.     

Investigation of the foil destruction dynamics in an explosively formed fuse opening switch by proton radiography

The dynamics of mechanical destruction of a conductor in an explosively formed fuse opening switch on a finned obstacle under the action of detonation products is studied in the injection channel of the U-70 proton synchrotron. Protonograms are recorded with digital multiframe electron-optic cameras. The exposure time per frame, about 30 ns, is determined by the duration of a proton bunch. The time from the beginning of motion of the conductor to its destruction is about 3 ??s. It is shown that the switch with typical sizes of the obstacle (the thickness of the fin is 1.5 mm, and the width and depth of the groove are 1.5 and 4.5 mm, respectively) provides operation with satisfactory gasdynamic parameters.     

Computational optimization analysis of a gas-jet target in a laser-plasma short-wave radiation source

A computational method is developed for optimizing the xenon gas jet used as the target in a laserplasma short-wave radiation source. The method is based on numerical hydrodynamic simulation of the jet flowing from the nozzle into vacuum, followed by computation of the optimization criterion describing the observed intensity of plasma glow. The application of this method permits an unambiguous and objective choice of optical experimental geometries and flow conditions; as a result, the radiation yield can be increased by several times. The calculated results are compared with available experimental data.     

LHC prospects in searches for neutral scalars in pp → γγ + jet

At hadron colliders, the γγ + jet channel provides a larger signal-to-background ratio in comparison with the inclusive γγ channel in hunting for scalars uncharged under the SM gauge group. By using NLO results for the SM Higgs boson production and corresponding background, we estimate LHC prospects in searches for the radion and sgoldstino in the γγ + jet channel. Three-body final-state kinematics allows for refined cuts. We have found that this channel could be comparable with the γγ channel in searches for new physics. The text was submitted by the authors in English.     

Electron spin-lattice relaxation in noncommon metals YBa2Cu3Ox and Rb1C60

Using an original modulation technique, the electron spin-lattice relaxation have been investigated in two noncommon metals: YBa₂Cu₃O_x, high-T_c material doped with 1% Gd, and Rb₁C₆₀, linear polymer phase fulleride. In the first case, the Korringa-like temperature dependence of the Gd³⁺ longitudinal relaxation time T₁, is found forx = 6.59 in a wide temperature range 4.2 <T < 200 K, both above and below T_c = 56 K. Atx = 6.95 (T_c = 90 K), the T₁ behavior within 50 <T < 200 K is evidently affected by spin gap opening with the gap value of about 240 K. At 200 K, an unexpected acceleration of the relaxation rate takes place, suggesting some change in the relaxation mechanism. The data are discussed in terms of the Barnes-Plefke theory with allowance made for microscopic separation of the normal and superconducting phases. In Rb₁C₆₀, the evolution of the ESR line and relaxation rates have been studied accurately in the range of the metal-insulator transition (below 50 K). Interpretation is suggested which takes into account breaking down the relaxation bottleneck due to opening of the energy gap near the Fermi surface. The gap value of about 100 cm^?1 is estimated from the analysis of relaxation rates, lineshape and spin susceptibilities.