406 research outputs found
Photon emission by ultra-relativistic positrons in crystalline undulators: the high-energy regime
This paper discusses the undulator radiation emitted by high-energy positrons
during planar channeling in periodically bent crystals. We demonstrate that the
construction of the undulator for positrons with energies of 10 GeV and above
is only possible if one takes into account the radiative energy losses. The
frequency of the undulator radiation depends on the energy of the particle.
Thus the decrease of the particle's energy during the passage of the crystal
should result in the destruction of the undulator radiation regime. However, we
demonstrate that it is possible to avoid the destructive influence of the
radiative losses on the frequency of the undulator radiation by the appropriate
variation of the shape of the crystal channels. We also discuss a method by
which, to our mind, it would be possible to prepare the crystal with the
desired properties of its channels.Comment: submitted for the proceedings of the International Workshop on
``Electron-Photon Interaction in Dense Media'' in Nor-Hamberd, Armenia, 2001;
10 pages, 9 figures, LaTe
Spontaneous and stimulated undulator radiation by an ultra-relativistic positron channeling in a periodically bent crystal
We discuss the radiation generated by positrons channeling in a crystalline
undulator. The undulator is produced by periodically bending a single crystal
with an amplitude much larger than the interplanar spacing. Different
approaches for bending the crystal are described and the restrictions on the
parameters of the bending are discussed. We also present numeric calculations
of the spontaneous emitted radiation and estimate the conditions for stimulated
emission. Our investigations show that the proposed mechanism could be an
interesting source for high energy photons and is worth to be studied
experimentally.Comment: long version of our contribution to the 22nd International Free
Electron Laser Conference, Durham, NC, USA, 13-18 August 2000, Reprinted from
Nuclear Instruments and Methods A, Volume 474, 1--3, in press, with
permission from Elsevier Science. http://www.elsevier.com/locate/nim
The influence of the structure imperfectness of a crystalline undulator on the emission spectrum
We study the influence of an imperfect structure of a crystalline undulator
on the spectrum of the undulator radiation. The main attention is paid to the
undulators in which the periodic bending in the bulk appears as a result of a
regular (periodic) surface deformations. We demonstrate that this method of
preparation of a crystalline undulator inevitably leads to a variation of the
bending amplitude over the crystal thickness and to the presence of the
subharmonics with smaller bending period. Both of these features noticeably
influence the monochromatic pattern of the undulator radiation.Comment: 26 pages, 9 figures, IOP style, submitted to NIM
Formalism of collective electron excitations in fullerenes
We present a detailed formalism for the description of collective electron
excitations in fullerenes in the process of the electron inelastic scattering.
Considering the system as a spherical shell of a finite width, we show that the
differential cross section is defined by three plasmon excitations, namely two
coupled modes of the surface plasmon and the volume plasmon. The interplay of
the three plasmons appears due to the electron diffraction of the fullerene
shell. Plasmon modes of different angular momenta provide dominating
contributions to the differential cross section depending on the transferred
momentum.Comment: 11 pages, 2 figures; submitted to the special issue "Atomic Cluster
Collisions: Structure and Dynamics from the Nuclear to the Biological Scale"
of Eur. Phys. J.
ЕАЭС: Макроэкономическая стабилизация в условиях глобального кризиса
В статье рассмотрены итоги первых двух лет функционирования Евразийского экономического союза. Проанализированы основные макроэкономические показатели стран–членов ЕАЭС, а также выполнение ими нормативов, характеризующих устойчивость развития экономического союза в соответствии с Договором о ЕАЭС. Рассмотрен комплекс мероприятий по созданию условий для устойчивого экономического роста стран–членов ЕАЭС. The article describes the results of the first two years of functioning of the Eurasian Economic Union. The main macroeconomic indicators of the EAEU member states and also their compliance with the standards that characterizes the sustainability of the development of the economic union in accordance with the Treaty on the EAEU are analyzed. The complex of measures on creation of conditions for sustainable economic growth of the EAEU member states is considered
New experimental data for the decays and from SND detector
The processes and have been
studied with SND detector at VEPP-2M collider in the vicinity of
resonance. The branching ratios and were obtained.Comment: 5 pages, 4 figures, talk given at 8th International Conference on
Hadron Spectroscopy (HADRON 99), Beijing, China, 24-28 Aug 199
The process in the energy range 2E_0=1.04 - 1.38 GeV
In the experiment with the SND detector at VEPP-2M e^+e^- collider the
process was studied in the energy range 2E_0 from
1.04 to 1.38 GeV. A broad peak was observed with the visible mass
MeV and cross section in the maximum
nb. The peak can be interpreted as a -like resonance .Comment: 10 pages LATEX and 5 figure
Experimental Study of rho -> pi0 pi0 gamma and omega -> pi0 pi0 gamma Decays
The e+e- -> pi0 pi0 gamma process was studied in the SND experiment at
VEPP-2M e+e- collider in the energy region 0.60-0.97 GeV. From the analysis of
the energy dependence of measured cross section the branching ratios B(omega ->
pi0 pi0 gamma)= (6.6 +1.4-0.8(stat) +-0.6(syst))x10^-5 and B(rho -> pi0 pi0
gamma)=(4.1 +1.0-0.9(stat) +-0.3(syst))x10^-5 were obtained.Comment: 16 pages, 7 figures, submitted to Phys. Lett.
Radiative decays of light vector mesons
The new data on radiative decays into
from SND experiment at VEPP-2M
collider are presented.Comment: 5 pages, 2 figures, talk given at 8th International Conference on
Hadron Spectroscopy (HADRON 99), Beijing, China, 24-28 Aug 199
Search for direct production of a2(1320) and f2(1270) mesons in e+e- annihilation
A search for direct production of C-even resonances a2(1320) and f2(1270) in
e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The
upper limits of electronic widths of these mesons were obtained at 90%
confidence level:
Gamma(a2(1320) \to e+e-) < 0.56 eV,
Gamma(f2(1270) \to e+e-) < 0.11 eV.Comment: 6 pages, 5 figures, 1 table. Submitted to Phys. Lett.
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