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A. I. Milstein

Publications and source records attributed to A. I. Milstein.

At least 127 records · Page 7Linked to original sources
arXiv2001

Experimental investigation of high-energy photon splitting in atomic fields

The new data analysis of the experiment, where the photon splitting in the atomic fields has been observed for the first time, is presented. This experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, the statistics of $1.6\cdot 10^9$ photons incident on the BGO target was collected. About 400 candidates to the photon splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the cross section calculated exactly in an atomic field. The predictions obtained in the Born approximation significantly differ from the experimental results.

hep-ex↗
arXiv2001

Parity nonconservation in heavy atoms: The radiative correction enhanced by the strong electric field of the nucleus

Parity nonconservation due to the nuclear weak charge is considered. We demonstrate that the radiative corrections to this effect due to the vacuum fluctuations of the characteristic size larger than the nuclear radius $r_0$ and smaller than the electron Compton wave-length $λ_C$ are enhanced because of the strong electric field of the nucleus. The parameter that allows one to classify the corrections is the large logarithm $\ln(λ_C/r_0)$. The vacuum polarization contribution is enhanced by the second power of the logarithm. Although the self-energy and the vertex corrections do not vanish, they contain only the first power of the logarithm. The value of the radiative correction is 0.4% for Cs and 0.9% for Tl, Pb, and Bi. We discuss also how the correction affects the interpretation of the experimental data on parity nonconservation in atoms.

hep-ph↗
arXiv2001

Structure of the Coulomb and unitarity corrections to the cross section of $e^+e^-$ pair production in ultra-relativistic nuclear collisions

We analyze the structure of the Coulomb and unitarity corrections to the single pair production as well as the cross section for the multiple pair production. In the external field approximation we consider the probability of $e^+e^-$ pair production at fixed impact parameter $ρ$ between colliding ultra-relativistic heavy nuclei. We obtain the analytical result for this probability at large $ρ$ as compared to the electron Compton wavelength. We estimate also the unitary corrections to the total cross section of the process.

hep-ph↗
arXiv2001

Relativistic corrections to the electromagnetic polarizabilities of compound systems

The low-energy amplitude of Compton scattering on the bound state of two charged particles of arbitrary masses, charges and spins is calculated. A case in which the bound state exists due to electromagnetic interaction (QED) is considered. The term, proportional to $ω^2$, is obtained taking into account the first relativistic correction. It is shown that the complete result for this correction differs essentially from the commonly used term $Δα$, proportional to the r.m.s. charge radius of the system. We propose that the same situation can take place in the more complicated case of hadrons.

hep-ph↗
arXiv2000

Status of Experiments and Recent Results from CMD-2 Detector at Vepp-2M

The Cryogenic Magnetic Detector (CMD-2) is shortly described. Preliminary results for the cross sections of $e^+$ $e^-$ annihilation into hadrons and leptons are presented in the c.m. energy range from 0.37 to 1.39 GeV. The total integrated luminosity of about 26 ${pb}^{-1}$ has been collected. The new results for the $ρ$ and $ω$ meson parameters are reported. The major decay modes of the $ϕ$ meson as well as its rare decays have been observed.

hep-ex↗
arXiv2000

a_1πContribution to e^+e^-\to 4πAnnihilation and τ\to 4πν_τ Decay

The results of the study of the process e^+e^- \to 4πby the CMD-2 collaboration at VEPP-2M are presented. Analysis of the differential distributions demonstrates the dominance of the a_1πand ωπintermediate states. Simple model, based on the assumption of a_1(1260)πand ωπdominance as intermediate states, successfully describes also the data of CLEOII and ALEPH obtained recently for the decay τ\to 4πν_τ.

hep-ex↗
arXiv1999

On the nature of Coulomb corrections to the e^+e^- pair production in ultrarelativistic heavy-ion collisions

We manifest the origin of the wrong conclusion made by several groups of authors on the absence of Coulomb corrections to the cross section of the e^+e^- pair production in ultrarelativistic heavy-ion collisions. The source of the mistake is connected with an incorrect passage to the limit in the expression for the cross section. When this error is eliminated, the Coulomb corrections do not vanish and agree with the results obtained within the Weizsäcker-Williams approximation.

hep-ph↗
arXiv1999

Quasiclassical Green function in an external field and small-angle scattering

The quasiclassical Green functions of the Dirac and Klein-Gordon equations in the external electric field are obtained with the first correction taken into account. The relevant potential is assumed to be localized, while its spherical symmetry is not required. Using these Green functions, the corresponding wave functions are found in the approximation similar to the Furry-Sommerfeld-Maue approximation. It is shown that the quasiclassical Green function does not coincide with the Green function obtained in the eikonal approximation and has a wider region of applicability. It is illustrated by the calculation of the small-angle scattering amplitude for a charged particle and the forward photon scattering amplitude. For charged particles, the first correction to the scattering amplitude in the non-spherically symmetric potential is found. This correction is proportional to the scattering angle. The real part of the amplitude of forward photon scattering in a screened Coulomb potential is obtained.

hep-ph↗
arXiv1999

On the role of $a_1(1260)$ meson in the $τ\to 4πν_τ$ decay

We demonstrate that a simple model successfully describing experimental data for the process $\epm\to 4π$ can also qualitatively account for the data of CLEOII and ALEPH obtained recently for the decay $τ\to 4πν_τ$. The model is based on the assumption of the $a_1(1260)π$ and $ωπ$ dominance as intermediate states. Our observation is in contrast with the claim by ARGUS that the $ρ$-meson signal in the $τ\to 4πν_τ$ decay can not be explained by the $a_1π$ intermediate state.

hep-ph↗
arXiv1999

Compton Scattering by Nuclei

The concept of Compton scattering by even-even nuclei from giant-resonance to nucleon-resonance energies and the status of experimental and theoretical researches in this field are outlined. Nuclear Compton scattering in the giant-resonance energy-region provides information on the dynamical properties of the in-medium mass of the nucleon. The electromagnetic polarizabilities of the nucleon in the nuclear medium can be extracted from nuclear Compton scattering data obtained in the quasi-deuteron energy-region. Recent results are presented for two-body effects due to the mesonic seagull amplitude and due to the excitation of nucleon internal degrees of freedom accompanied by meson exchanges. Due to these studies the in-medium electromagnetic polarizabilities are by now well understood, whereas the understanding of nuclear Compton scattering in the Delta-resonance range is only at the beginning. Phenomenological methods how to include retardation effects in the scattering amplitude are discussed and compared with model predictions.

nucl-th↗
arXiv1999

Simple analytical representation for the high-energy Delbruck scattering amplitudes

Using a new representation for the quasiclassical Green function of the Dirac equation in a Coulomb field, analytical expressions for the high-energy small-angle Delbrück scattering amplitudes are obtained exactly in the parameter Zα. Magnitudes of the amplitudes coincide with the previous results. However, the structure of the expressions obtained is much more simple, which considerably facilitates numerical calculations.

hep-ph↗
arXiv1998

Delbrück scattering at energies 140 - 450 MeV

The differential cross section of Delbrück scattering is measured on a bismuth germanate $Bi_4Ge_3O_{12}$ target at photon energies $140 - 450 MeV$ and scattering angles $2.6 - 16.6 mrad$. A good agreement with the theoretical results, obtained exactly in a Coulomb field, is found.

hep-ex↗
arXiv1998

Cross section of high-energy photon splitting in the electric fields of heavy atoms

Various differential cross sections of high-energy photon splitting in the electric fields of heavy atoms are calculated exactly in the parameter \al. The consideration is based on the quasiclassical approach applicable for small angles between all photon momenta. The expressions obtained are valid for arbitrary transverse momenta of final photons . The detailed investigation of the process is performed taking into account the effect of screening . The exact cross section turns out to be noticeably smaller than the result obtained in the Born approximation.

hep-ph↗
arXiv1997

Large Coulomb corrections in high-energy photon splitting

The Coulomb corrections to the helicity amplitudes of high-energy photon splitting are examined. The consideration is based on the amplitudes obtained exactly in the parameter Zαwithin the quasiclassical approach valid for small angles between all photon momenta. We consider the case when the transverse momenta of both final photons are much larger than the electron mass. It is shown that at Zα\sim 1 the Coulomb corrections essentially change the result for the cross section as compared to the Born approximation. The effect of screening is also taken into account.

hep-ph↗
arXiv1997

Meson-induced correlations of nucleons in nuclear Compton scattering

The non-resonant (seagull) contribution to the nuclear Compton amplitude at low energies is strongly influenced by nucleon correlations arising from meson exchange. We study this problem in a modified Fermi gas model, where nuclear correlation functions are obtained with the help of perturbation theory. The dependence of the mesonic seagull amplitude on the nuclear radius is investigated and the influence of a realistic nuclear density on this amplitude is dicussed. We found that different form factors appear for the static part (proportional to the enhancement constant $κ$) of the mesonic seagull amplitude and for the parts, which contain the contribution from electromagnetic polarizabilities.

nucl-th↗
arXiv1997

High-energy photon splitting in a strong Coulomb field

The helicity amplitudes of the high-energy photon splitting in the external Coulomb field are obtained exactly in the parameter $\al$. The cases of screened and unscreened potentials are investigated. The consideration is based on the quasiclassical approach, valid for small angles between all photon momenta. New representation of the quasiclassical electron Green function is exploited. General expressions obtained are analyzed in detail for the case of large transverse momenta of both final photons compared to the electron mass.

hep-ph↗