arXiv subjects

V. N. Baier

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

At least 19 recordsLinked to original sources

arXiv2009

Pair creation by a photon in an electric field

The process of pair creation by a photon in a constant and homogeneous electric field is investigated basing on the polarization operator in the field. The total probability of the process is found in a relatively simple form. At high energy the quasiclassical approximation is valid. The corrections to the standard quasiclassical approximation (SQA) are calculated. In the region relatively low photon energies, where SQA is unapplicable, the new approximation is used. It is shown that in this energy interval the probability of pair creation by a photon in electric field exceeds essentially the corresponding probability in a magnetic field. This approach is valid at the photon energy much larger than "vacuum" energy in electric field: $ω\gg eE/m$. For smaller photon energies the low energy approximation is developed. At $ω\ll eE/m$ the found probability describes the absorption of soft photon by the particles created by an electric field.

hep-ph↗

arXiv2009

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)

hep-ph↗

arXiv2008

Electroproduction of electron-positron pair in oriented crystal at high energy

The process of electroproduction of the electron-positron pair by high energy electron in an oriented single crystal is investigated. Two contributions are considered: the direct (one-step) process via the virtual intermediate photon and the cascade(two-step) process when the electron emits the real photon moving in the field of axis and afterwards the photon converts into the pair. The spectrum of created positron(electron) is found. It is shown that the probability of the process is strongly enhanced comparing with the corresponding amorphous medium.

hep-ph↗

arXiv2008

Electroproduction of electron-positron pair in a medium

The process of electron-positron pair creation by a high-energy electron in a medium is analyzed. The spectral distribution over energies of created particles is calculated for the direct and cascade mechanisms of the process. The Coulomb corrections are included. The new formulation of the equivalent photons method is developed which takes into account the influence of multiple scattering. It is shown the effects of multiple scattering can be quite effectively studied in the process under consideration.

hep-ph↗

arXiv2007

Opportunity to study the LPM effect in oriented crystal at GeV energy

The spectral distribution of electron-positron pair created by photon and the spectral distribution of photons radiated from high-energy electron in an oriented single crystal is calculated using the method which permits inseparable consideration both of the coherent and incoherent mechanisms of two relevant processes. The method includes the action of field of axis (or plane) as well as the multiple scattering of radiating electron or particles of the created pair (the Landau-Pomeranchuk-Migdal (LPM) effect). The influence of scattering on the coherent mechanism and the influence of field on the incoherent mechanism are analyzed. In tungsten, axis $<111>$ for the pair creation process at temperature T= 100 K the LPM effect attains 8 % at photon energy 5 GeV and for the radiation process at T= 293 K the LPM effect reaches 6 % at electron energy 10 GeV.

hep-ph↗

arXiv2007

Spectrum and polarization of coherent and incoherent radiation and the LPM effect in oriented single crystal

The spectrum and the circular polarization of radiation from longitudinally polarized high-energy electrons in oriented single crystal are considered using the method which permits inseparable consideration of both the coherent and the incoherent mechanisms of photon emission. The spectral and polarization properties of radiation are obtained and analyzed. It is found that in some part of spectral distribution the influence of multiple scattering (the Landau-Pomeranchuk-Migdal (LPM) effect) attains the order of 7 percent. The same is true for the influence of multiple scattering on the polarization part of the radiation intensity. The degree of circular polarization of total intensity of radiation is found. It is shown that the influence of multiple scattering on the photon polarization is similar to the influence of the LPM effect on the total intensity of radiation: it appears only for relatively low energies of radiating electron and has the order of 1 percent, while at higher energies the crystal field action excludes the LPM effect.

hep-ph↗

arXiv2007

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 $B \ll B_0, (B_0$ 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 $B \ll B_0$ and $B \geq B_0$ 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.

hep-ph↗

arXiv2006

Forty years of acting electron-positron colliders

Around forty years passed from the beginning of operation of the first electron-positron colliding beam facility VEPP-2 in Institute of Nuclear Physics (INP), Novosibirsk. Here I described development of electron-positron colliding beam project in INP, as well as advance of similar projects of the first generation at LAL, Orsay and at LNF, Frascati.

hep-ph↗

arXiv2006

Coherent and incoherent processes and the LPM effect in oriented single crystals at high-energy

The process of radiation from high-energy electron and electron-positron pair production by a photon in oriented single crystal is considered using the method which permits inseparable consideration of both coherent and incoherent mechanisms of photon emission from an electron and of pair creation by a photon and includes the action of field of axis (or plane) as well as the multiple scattering of radiating electron or particles of the created pair (the Landau-Pomeranchuk-Migdal (LPM) effect). The total intensity of radiation and total probability pair creation are calculated. The theory, where the energy loss of projectile has to be taken into account, and found probabilities of pair creation agree quite satisfactory with available CERN data. From obtained results it follows that multiple scattering appears only for relatively low energy of radiating electron or a photon, while at higher energies the field action excludes the LPM effect.

hep-ph↗

arXiv2005

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.

hep-ph↗

arXiv2005

Polarization effects for pair creation by photon in oriented crystals at high energy

Pair creation by a photon in an oriented crystal is considered in a frame of the quasiclassical operator method, which includes processes with polarized particles. Under some quite generic assumptions the general expression is derived for the probability of pair creation of longitudinally polarized electron (positron) by circularly polarized photon in oriented crystal. In particular cases $\vartheta_0 \ll V_0/m$ and $\vartheta_0 \gg V_0/m$ ($\vartheta_0$ is the angle of incidence, angle between the momentum of initial photon and axis (plane) of crystal, $V_0$ is the scale of a potential of axis or a plane relative to which the angle $\vartheta_0$ is defined) one has constant field approximation and the coherent pair production theory correspondingly. Side by side with coherent process the probability of incoherent pair creation is calculated, which differs essentially from amorphous one. At high energy the pair creation in oriented crystals is strongly enhanced comparing with amorphous medium. In appendixes the integral polarization of positron is found in external field and for coherent and incoherent mechanisms.

hep-ph↗

arXiv2005

Coherent and incoherent pair creation by a photon in oriented single crystal

The new approach is developed for study of electron-positron pair production by a photon in oriented single crystal. It permits indivisible consideration of both coherent and incoherent mechanisms of pair creation and includes the action of field of axis (or plane) as well as the multiple scattering of particles of the created pair (the Landau-Pomeranchuk-Migdal (LPM) effect). From obtained integral probability of pair creation, it follows that multiple scattering appears only for relatively low energy of photon, while at higher photon energy the field action excludes the LPM effect. The found results agree quite satisfactory with recent CERN experiment.

hep-ph↗

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↗