845 research outputs found
New analysis of semileptonic B decays in the relativistic quark model
We present the new analysis of the semileptonic B decays in the framework of
the relativistic quark model based on the quasipotential approach. Decays both
to heavy D^{(*)} and light \pi(\rho) mesons are considered. All relativistic
effects are systematically taken into account including contributions of the
negative-energy states and the wave function transformation from the rest to
moving reference frame. For heavy-to-heavy transitions the heavy quark
expansion is applied. Leading and subleading Isgur-Wise functions are
determined as the overlap integrals of initial and final meson wave functions.
For heavy-to-light transitions the explicit relativistic expressions are used
to determine the dependence of the form factors on the momentum transfer
squared. Such treatment significantly reduces theoretical uncertainties and
increases reliability of obtained predictions. All results for form factors,
partial and total decay rates agree well with recent experimental data and
unquenched lattice calculations. From this comparison we find the following
values of the Cabibbo-Kobayashi-Maskawa matrix elements:
|V_{cb}|=(3.85\pm0.15\pm 0.20)*10^{-2} and
|V_{ub}|=(3.82\pm0.20\pm0.20)*10^{-3}, where the first error is experimental
and the second one is theoretical.Comment: 25 pages, 11 figure
Effect of the sample geometry on the second magnetization peak in single crystalline BaKBiO thick film
Magnetization hysteresis loop measurements performed on a single
crystalline BaKBiO superconducting thick film reveal
pronounced sample geometry dependence of the "second magnetization peak" (SMP),
i.e. a maximum in the width of occurring at the field .
In particular, it is found that the SMP vanishes decreasing the film dimension.
We argue that the observed sample geometry dependence of the SMP cannot be
accounted for by models which assume a vortex pinning enhancement as the origin
of the SMP. Our results can be understood considering the thermomagnetic
instability effect and/or non-uniform current distribution at
in large enough samples.Comment: 8 pages 3 figure
Lateral-angular and temporal characteristics of EAS optical radiation
Characteristics of the direct and scattered components of electron-photon shower optical radiation for distances R 500 m from the shower core to a detector, allowing for the Cerenkov and fluorescent mechanism of photon generation are presented. The results of calculations are employed to clarify the techniques for determination of the shower parameters detected by both installations registering fluorescent light and those recording Cerenkov light
Relativistic Description of Exclusive Semileptonic Decays of Heavy Mesons
Using quasipotential approach, we have studied exclusive semileptonic decays
of heavy mesons with the account of relativistic effects. Due to more complete
relativistic description of the quark more precise expressions for
semileptonic form factors are obtained. Various differential distributions in
exclusive semileptonic decays of heavy mesons are calculated. It is argued that
consistent account of relativistic effects and HQET motivated choice of the
parameters of quark-antiquark potential allow to get reliable value for the
ratio in the decay as well as the
ratio~. All calculated branching
ratios are in accord with available experimental data.Comment: 18 pages, LATEX, 2 figures inclosed + 4 Postscript figure
Masses of heavy baryons in the relativistic quark model
The masses of the ground state heavy baryons consisting of two light (u,d,s)
and one heavy (c,b) quarks are calculated in the heavy-quark--light-diquark
approximation within the constituent quark model. The light quarks, forming the
diquark, and the light diquark in the baryon are treated completely
relativistically. The expansion in v/c up to the second order is used only for
the heavy (b and c) quarks. The diquark-gluon interaction is taken modified by
the form factor describing the light diquark structure in terms of the diquark
wave functions. An overall reasonable agreement of the obtained predictions
with available experimental data and previous theoretical results is found.Comment: 13 pages, 2 figures, version published in Phys. Rev.
Microscopic study of electrical properties of CrSi2 nanocrystals in silicon
Semiconducting CrSi2 nanocrystallites (NCs) were grown by reactive deposition epitaxy of Cr onto n-type silicon and covered with a 50-nm epitaxial silicon cap. Two types of samples were investigated: in one of them, the NCs were localized near the deposition depth, and in the other they migrated near the surface. The electrical characteristics were investigated in Schottky junctions by current-voltage and capacitance-voltage measurements. Atomic force microscopy (AFM), conductive AFM and scanning probe capacitance microscopy (SCM) were applied to reveal morphology and local electrical properties. The scanning probe methods yielded specific information, and tapping-mode AFM has shown up to 13-nm-high large-area protrusions not seen in the contact-mode AFM. The electrical interaction of the vibrating scanning tip results in virtual deformation of the surface. SCM has revealed NCs deep below the surface not seen by AFM. The electrically active probe yielded significantly better spatial resolution than AFM. The conductive AFM measurements have shown that the Cr-related point defects near the surface are responsible for the leakage of the macroscopic Schottky junctions, and also that NCs near the surface are sensitive to the mechanical and electrical stress induced by the scanning probe
Sensitivity of depth of maximum and absorption depth of EAS to hadron production mechanism
Comparison of experimental data on depth of extensive air showers (EAS) development maximum in the atmosphere, T sub M and path of absorption, lambda, in the lower atmosphere of EAS with fixed particle number in the energy region eV with the results of calculation show that these parameters are sensitive mainly to the inelastic interaction cross section and scaling violation in the fragmentation and pionization region. The data are explained in a unified manner within the framework of a model in which scaling is violated slightly in the fragmentation region and strongly in the pionization region at primary cosmic rays composition close to the normal one and a permanent increase of inelastic interaction cross section. It is shown that, while interpreting the experimental data, disregard of two methodical points causes a systematic shift in T sub M: (1) shower selection system; and (2) EAS electron lateral distribution when performing the calculations on basis of which the transfer is made from the Cerenkov pulse FWHM to the depth of shower maximum, T sub M
Nucleon-nucleon wave function with short-range nodes and high-energy deuteron photodisintegration
We review a concept of the Moscow potential (MP) of the interaction. On
the basis of this concept we derive by quantum inversion optical partial
potentials from the modern partial-wave analysis (PWA) data and deuteron
properties. Point-form (PF) relativistic quantum mechanics (RQM) is applied to
the two-body deuteron photodisintegration. Calculations of the cross-section
angular distributions cover photon energies between 1.1 and 2.5 GeV. Good
agreement between our theory and recent experimental data confirms the concept
of deep attractive Moscow potential with forbidden - and -states.Comment: 31 pages, 9 figures. typos, extended formalism, review of the Moscow
potential model adde
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