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V. N. Baier

Publications and source records attributed to V. N. Baier.

At least 37 records · Page 2Linked to original sources
arXiv2003

On coherent radiation in electron-positron colliders

The electromagnetic processes in linear colliders are discussed on the basis of quasiclassical operator method. The complete set of expressions is written down for spectral probability of radiation from an electron and pair creation by a photon taking into account both electron and photon polarization. Some new formulas are derived for radiation intensity and its asymptotics. The main mechanisms of pair creation dominate at $χ\leq 1$ are discussed.

hep-ph↗
arXiv2002

Deviation from standard QED at large distances: influence of transverse dimensions of colliding beams on bremsstrahlung

The radiation at collision of high-energy particles is formed over a rather long distances and therefore is sensitive to an environment. In particular the smallness of the transverse dimensions of the colliding beams leads to suppression of bremsstrahlung cross section for soft photons. This beam-size effect was discovered and investigated at INP, Novosibirsk around 1980. At that time an incomplete expression for the bremsstrahlung spectrum was calculated and used because a subtraction associated with the extraction of pure fluctuation process was not performed. Here this procedure is done. The complete expression for the spectral-angular distribution of incoherent bremsstrahlung probability is obtained. The case of Gaussian colliding beams is investigated in details. In the case of flat beams the expressions for the bremsstrahlung spectrum are simplified essentially. Comparison of theory with VEPP4 and HERA data is performed. Possible application of the effect to linear $e^+e^-$ collider tuning is discussed.

hep-ph↗
arXiv2002

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 <111> - axis of the tungsten crystals.

hep-ph↗
arXiv2001

On propagation of high-energy photon in a medium in presence of an external field

The polarization tensor is calculated which originates from interaction of a photon with the electron-positron field. The effects of multiple scattering of electrons and positrons in a medium side by side with an external field are included. The corresponding general representation of polarization tensor is found in the form of two-dimentional integral. The both effects may be essential for propagation of high-energy photons in oriented single crystals.

hep-ph↗
arXiv2000

Integral characteristics of bremsstrahlung and pair photoproduction in a medium

The bremsstrahlung of an electron and $e^{-}e^{+}$-pair creation by a photon in a medium is considered in high-energy region, where influence of the multiple scattering on the processes (the Landau-Pomeranchuk-Migdal (LPM) effect) becomes essential. The integral characteristics: the radiation length and the total probability of radiation and pair photoproduction are analyzed under influence of the LPM effect.

hep-ph↗
arXiv2000

Anomalous magnetic moment of the electron in a medium

Radiative effects are considered for an electron moving in a medium in the presence of an external electromagnetic field. Anomalous magnetic moment (AMM) of the electron in alpha-order is calculated under these conditions in the form of two-dimensional integral. Behavior of AMM of high energy electron under influence of multiple scattering in a medium is analyzed. Both mentioned effects lead to reduction of AMM.

hep-ph↗
arXiv2000

Influence of a medium on coherent scattering of high-energy photon

The coherent scattering of photon in the Coulomb field (the Delbrück scattering) is considered for the momentum transfer $Δ\ll m$ in the frame of the quasiclassical operator method. In high-energy region this process occurs over rather long distance. The process amplitude is calculated taking into account the multiple scattering of particles of the intermediate electron-positron pair in a medium. The result is the suppression of the process.

hep-ph↗
arXiv2000

Coherent scattering of high-energy photon in a medium

The coherent scattering of photon in the Coulomb field (the Delbrück scattering) is considered for the momentum transfer $Δ\ll m$ in the frame of the quasiclassical operator method. In high-energy region this process occurs over rather long distance. The process amplitude is calculated taking into account the multiple scattering of particles of the intermediate electron-positron pair in a medium. The result is the suppression of the process. Limiting cases of weak and strong effects of the multiple scattering are analyzed. The approach used is the generalization of the method developed by authors for consideration of the Landau-Pomeranchuk-Migdal effect.

hep-ph↗
arXiv2000

Influence of a medium on pair photoproduction and bremsstrahlung

The creation of electron-positron pair by a photon and the bremsstrahlung of an electron in a medium are considered in high-energy region, where influence of the multiple scattering on the processes (the Landau-Pomeranchuk-Migdal (LPM) effect) becomes essential. The pair photoproduction probability is calculated with an accuracy up to the "next to leading logarithm". The integral characteristics: the radiation length and the total probability of pair photoproduction are analyzed under influence of the LPM effect, and the asymptotic expansions of these characteristics are derived.

hep-ph↗
arXiv1999

On Basic Concepts of the Quasiclassical Operator Approach

We present a derivation of the probability of bremsstrahlung from high-energy electrons in a screened Coulomb field using the quasiclassical operator method. It is shown that recent Zakharov's criticism is completely groundless and comes from misunderstanding of the method. We confirm all our published results.

hep-ph↗
arXiv1999

Sum rules for 1/m corrections to the form factors of semileptonic B decays

Semileptonic B decays are described by the Isgur-Wise form factor to the leading order in 1/m; four new functions appear in the first order [Luke]. Values of these functions are crucial for the applicability of the whole approach to processes involving c quark. We obtain the sum rules for three subleading form factors from the QCD sum rules with finite masses by expanding to the first order in 1/m. The results respect the pattern of the first 1/m corrections established in HQET, and obey the Luke's theorem. The numerical estimates show that 1/m_c corrections are sizable but not catastrophic.

hep-ph↗
arXiv1999

The Landau-Pomeranchuk-Migdal effect and transition radiation in structured targets

The radiation from high-energy electrons is investigated for the case when a target consists of several separated plates. The spectrum of radiation is considered in the region in which the bremsstrahlung is under influence of the multiple scattering of a projectile (the LPM effect), the polarization of a medium and the hard part of the boundary radiation contribute. In this region the general expression for the radiation spectrum is obtained for the $N$-plate target. A qualitative description of the arising interference pattern is given.

hep-ph↗
arXiv1998

Transition radiation as a source of quasi-monochromatic X-rays

Transition radiation (TR) from ultrarelativistic particles is considered. It is shown that performing collimation of the TR from the periodic N-foil stack (parameters of which are selected in a appropriate manner) one obtains the spectrum of the TR which has a form of a peak position of which $ω_1$ depends on the plasma frequency and the thickness of the radiator foils. The height and width of the peak depend on the collimation angle $\vartheta_c$. The height of the peak for given $\vartheta_c$ is proportional to N. Selecting parameters one can have the source of X-rays of desired frequency with rather good monochromaticity.

hep-ex↗
arXiv1998

Quantum theory of transition radiation and transition pair creation

Theory of the transition radiation and the transition pair creation is developed in the frame of QED. The spectral-angular distributions of probability of the transition radiation and of the transition pair creation are found. The total energy losses of and the total probability of pair creation are calculated and analyzed. Features of radiation and pair creation processes in a superdence medium (typical for white dwarfs) are discussed.

hep-ph↗
arXiv1998

Multi-photon effects in energy losses spectra

Effect of radiation of many photons by a single electron traversing a target is discussed. When the summary energy of emitted photons (the energy losses spectrum) is measured only, the photon spectrum is distorted comparing with the photon spectrum in one interaction. Influence of this effect is discussed for the cases (1) bremsstrahlung (described by Bethe-Heitler formula), (2) the strong Landau-Pomeranchuk-Migdal effect and (3) transition radiation. Qualitative picture of the phenomenon is discussed in detail. Comparison with the recent SLAC experiment in relatively thick target (2.7% of the radiation length), where the effect of emission of many photons by a projectile is very essential, shows perfect agreement of the theory and data.

hep-ph↗
arXiv1997

The Landau-Pomeranchuk-Migdal effect in a thin target

The Landau, Pomeranchuk, Migdal (LPM) effect (suppression of the bremsstrahlung from high energy electron due to a multiple scattering of an emitting electron in dense media) is considered for the case when thickness of a target is of the order or less than the formation length of radiation. The effects of the polarization of a medium and transition radiation are taken into account as well. Qualitative picture of the phenomenon is discussed in detail. Comparison with recent experimental data is carried out.

hep-ph↗
arXiv1997

The theory of the Landau, Pomeranchuk, Migdal effect

Bremsstrahlung of photons from highly relativistic electrons is investigated. The cross section of the processes, which is suppressed due to a multiple scattering of an emitting electron in dense media (LPM effect) and due to photon interaction with electrons of a medium, is calculated with an accuracy up to "next to leading logarithm" and with the Coulomb corrections taken into account. Making allowances for a multiple scattering and a polarization of a medium an analysis of radiation on a target boundary is carried out. The method of consideration of radiation in a thin target under influence of the LPM effect is developed. Interrelation with the recent experiment is discussed.

hep-ph↗