2,070 research outputs found
Comparison of theory with experiment for positron production from high-energy electrons moving along crystal axes
Various positron distributions are obtained using an approach developed
earlier for the description of electron-photon showers in axially aligned
single crystals. Based on these distributions, characteristics of the positron
yield measured in recent experiments are calculated. Theoretical estimations
display a rather good agreement with experimental results obtained using 3 to
10 GeV electrons aligned to the - axis of the tungsten crystals.Comment: 10 pages, 6 Postscript figure
Pair creation by a photon in a strong magnetic field
The process of pair creation by a photon in a strong magnetic field is
investigated basing on the polarization operator in the field. The total
probability of the process is found in a relatively simple form. The
probability exhibits a "saw-tooth" pattern because of divergences arising when
the electron and positron are created at threshold of the Landau energy levels.
The pattern will be washed out at averaging over any smooth photon energy
distribution. The new results are obtained in the scope of the quasiclassical
approach: 1) in the case when the magnetic field is the
critical field) the new formulation extends the photon energy interval to the
case when the created particles are not ultrarelativistic; 2) the correction to
the standard quasiclassical approximation is found showing the range of
applicability of the approach at high photon energy as well. The very important
conclusion is that for both cases and the results of
the quasiclassical calculation are very close to averaged probabilities of
exact theory in a very wide range of photon energies. The quasiclassical
approximation is valid also for the energy distribution if the electron and
positron are created on enough high levels.Comment: 21 pages, 6 figure
Spectra of radiation and created particles at intermediate energy in oriented crystal taking into account energy loss
The spectral distribution of positron created by photon and the spectral
distribution of photons radiated from electron in an oriented single crystal of
intermediate thickness is calculated at intermediate energies. The energy loss
of charged particles as well as photon absorption are taken into account. The
used basic probabilities of processes include the action of field of axis as
well as the multiple scattering of radiating electron or particles of the
created pair (the Landau-Pomeranchuk-Migdal (LPM) effect)Comment: 11 pages, 5 figures, report at "Channeling 2008" Workshop, Erice,
Italy, October 200
Beam-size effect in Bremsstrahlung
The smallness of the transverse dimensions of the colliding beams leads to
suppression of bremsstrahlung cross section. This beam-size effect was
discovered and investigated at INP, Novosibirsk. Different mechanisms of
radiation are discussed. Separation of coherent and incoherent radiation is
analyzed in detail. For linear collider this suppression affects the whole
radiation spectrum. It is shown that objections to the subtraction procedure in
\cite{BK2} are groundless.Comment: Plenary talk at the Workshop "Quantum Aspects of Beam Physics",
Hiroshima, Japan, January 7-11, 2003. To be pulished in the Proceedings
(World Scientific, Singapore
Coherent and incoherent radiation from high-energy electron and the LPM effect in oriented single crystal
The process of radiation from high-energy electron in oriented single crystal
is considered using the method which permits inseparable consideration of both
coherent and incoherent mechanisms of photon emission. The total intensity of
radiation is calculated. The theory, where the energy loss of projectile has to
be taken into account, agrees quite satisfactory with available CERN data. It
is shown that the influence of multiple scattering on radiation process is
suppressed due to action of crystal field.Comment: 15 pages, 3 figure
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