arXiv subjects

V. M. Katkov

Publications and source records attributed to V. M. Katkov.

At least 37 records · Page 2Linked to original sources

arXiv2004

Effects of polarization in electromagnetic processes in oriented crystals at high energy

Under quite generic assumptions the general expression is derived for the probability of circularly polarized photon emission from the longitudinally polarized electron and for the probability of pair creation of longitudinally polarized electron (positron) by circularly polarized photon in oriented crystal in a frame of the quasiclassical operator method. For small angle of incidence the expression turns into constant field limit with corrections due to inhomogeneous character of field in crystal. For relatively large angle of incidence the expression gets over into the theory of coherent radiation or pair creation. It is shown that the crystal is a very effective device for helicity transfer from an electron to photon and back from a photon to electron or positron.

hep-ph↗

arXiv2004

Radiation from polarized electrons in oriented crystals at high energy

Radiation from high energy electrons in an oriented crystal can be considered in a frame of the quasiclassical operator method which appears to be a most satisfactory approach to the problem. Under some quite generic assumptions the general expression is derived for the probability of circularly polarized photon emission from the longitudinally polarized electron in oriented crystal. The particular mechanism of radiation depends on interrelation between the angle of incidence $\vartheta_0$ (angle between the momentum of initial electron and axis (plane) of crystal) and angle $\vartheta_v \equiv V_0/m$ ($V_0$ is the scale of a potential of axis or a plane relative to which the angle $\vartheta_0$ is defined). When $\vartheta_0 \ll \vartheta_v$ one has magnetic bremsstrahlung type of radiation (with corrections $\propto \vartheta_0^2$ which are due to inhomogeneous character of field in crystal). When $\vartheta_0 \gg \vartheta_v$ one obtains the theory of coherent bremsstrahlung, while for $\vartheta_0 \geq \vartheta_v$ one arrives to the modified theory of coherent bremsstrahlung. At high energy radiation in oriented crystals is strongly enhanced comparing with standard bremsstrahlung.

hep-ph↗

arXiv2004

Variation of radiation length due to LPM effect

The photon emission intensity spectrum is calculated taking into account influence of multiple scattering (the LPM effect) under conditions of recent CERN SPS experiment. It is shown that the theory quite satisfactory describes data. The integral characteristics: the radiation length and total probability of photon emission are analyzed under influence of the LPM effect, and the asymptotic expansions of these characteristics are derived.

hep-ph↗

arXiv2004

Concept of Formation Length in Radiation Theory

The features of electromagnetic processes are considered which connected with finite size of space region in which final particles (photon, electron-positron pair) are formed. The longitudinal dimension of the region is known as the formation length. If some external agent is acting on an electron while traveling this distance the emission process can be disrupted. There are different agents: multiple scattering of projectile, polarization of a medium, action of external fields, etc. The theory of radiation under influence of the multiple scattering, the Landau-Pomeranchuk-Migdal (LPM) effect, is presented. The probability of radiation is calculated with an accuracy up to "next to leading logarithm" and with the Coulomb corrections taken into account. The integral characteristics of bremsstrahlung are given, it is shown that the effective radiation length increases due to the LPM effect at high energy. The LPM effect for pair creation is also presented. The multiple scattering influences also on radiative corrections in a medium (and an external field too) including the anomalous magnetic moment of an electron and the polarization tensor as well as coherent scattering of a photon in a Coulomb field. The polarization of a medium alters the radiation probability in soft part of spectrum. Specific features of radiation from a target of finite thickness include: the boundary photon emission, interference effects for thin target, multi-photon radiation. The experimental study of LPM effect is described. For electron-positron colliding beams following items are discussed: the separation of coherent and incoherent mechanisms of radiation, the beam-size effect in bremsstrahlung, coherent radiation and mechanisms of electron-positron creation.

hep-ph↗

arXiv2003

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.

hep-ph↗

arXiv2003

On theory of Landau-Pomeranchuk-Migdal effect

The cross section of bremsstrahlung from high-energy electron suppressed due to the multiple scattering of an emitting electron in a dense media (the LPM effect) is discussed. Development of the LPM effect theory is outlined. For the target of finite thickness one has to include boundary photon radiation as well as the interference effects. The importance of multiphoton effects is emphasized. Comparison of theory with SLAC data is presented.

hep-ph↗

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↗

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

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

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↗