1,569 research outputs found
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
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
Delbr\"uck scattering in combined Coulomb and laser fields
We study Delbr\"uck scattering in a Coulomb field in the presence of a laser
field. The amplitudes are calculated in the Born approximation with respect to
the Coulomb field and exactly in the parameters of the laser field having
arbitrary strength, spectral content and polarization. The case of high energy
initial photon energy is investigated in detail for a monochromatic circularly
polarized laser field. It is shown that the angular distribution of the process
substantially differs from that for Delbr\"uck scattering in a pure Coulomb
field. The value of the cross section under discussion may exceed the latter at
realistic laser parameters that essentially simplify the possibility of the
experimental observation of the phenomenon. The effect of high order terms in
the quantum intensity parameter of the laser field is found to be very
important already at relatively small .Comment: 21 pages, 4 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
Photon splitting in a laser field
Photon splitting due to vacuum polarization in a laser field is considered.
Using an operator technique, we derive the amplitudes for arbitrary strength,
spectral content and polarization of the laser field. The case of a
monochromatic circularly polarized laser field is studied in detail and the
amplitudes are obtained as three-fold integrals. The asymptotic behavior of the
amplitudes for various limits of interest are investigated also in the case of
a linearly polarized laser field. Using the obtained results, the possibility
of experimental observation of the process is discussed.Comment: 31 pages, 4 figure
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
Coulomb effects in the spin-dependent contribution to the intra-beam scattering rate
Coulomb effects in the intra-beam scattering are taken into account in a way
providing correct description of the spin-dependent contribution to the beam
loss rate. It allows one to calculate this rate for polarized beams
at arbitrarily small values of the ratio ,
characterizing relative change of the electron energy in the laboratory system
during scattering event.Comment: 8 pages, 2 figure
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