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A. I. Milstein

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

At least 37 records · Page 2Linked to original sources
arXiv2023

Coupled channels and production of near-threshold $B^{(*)}\bar{B}^{(*)}$ resonances in $e^{+}e^{-}$ annihilation

The effects of final-state interaction of hadrons, produced in $e^{+}e^{-}$ annihilation near the threshold, are discussed. If there is a loosely bound state or a virtual state in a system of produced hadrons, then the energy dependence of hadroproduction cross section is very strong. Our approach is based on the use of the effective potentials accounting for the interaction between hadrons in the final state. The cases of a few channels with nonzero transition amplitudes between them are considered. It is shown that these transitions drastically change the energy dependence of the cross sections. In particular, a narrow resonance below the threshold in one channel leads to a broad peak in another channel. We explained the non-trivial energy dependence of the production cross sections of $B\bar{B}$, $B^{*}\bar{B}$, $B\bar{B}^{*}$, $B^{*}\bar{B}^{*}$ near the thresholds in $e^{+}e^{-}$ annihilation and obtained good agreement between our predictions and the experimental data available.

hep-ph↗
arXiv2023

Natural explanation of recent results on $e^{+}e^{-}\toΛ\barΛ$

We show that the recent experimental data on the cross section of the process $e^{+}e^{-}\toΛ\barΛ$ near the threshold can be perfectly explained by the final-state interaction of $Λ$ and $\barΛ$. The enhancement of the cross section is related to the existence of low-energy real or virtual state in the corresponding potential. We present a simple analytical formula that fits the experimental data very well.

hep-ph↗
arXiv2023

Manifestation of the electric dipole moment in the decays of $τ$ leptons produced in $e^+e^-$ annihilation

$\mbox{CP}$-odd asymmetries in the processes $e^+e^-\rightarrow τ^+π^-ν_τ$, $e^+e^-\rightarrow π^+τ^-\barν_ τ$, $e^+e^-\rightarrow τ^+ρ^-ν_τ$, $e^+e^-\rightarrow ρ^+τ^-\barν_τ$, $e^+e^-\to τ^+e^-ν_τ{\barν}_e\,,\,$ and $\,e^+e^-\to τ^-e^+ν_e{\barν}_τ$ are investigated with account for longitudinal polarization of electron (or positron) beam. These asymmetries is a manifestation of electric dipole form factor $F_3^τ\equiv b$ in the $γτ^+τ^-$ vertex. It is shown that, to measure $\mbox{Im}\,b$ in the specified processes, polarization is not needed, while to measure $\mbox{Re}\,b$ it is required. The processes $e^+e^-\to π^+π^-ν_τ{\barν}_τ$, $e^+e^-\to e^+e^-ν_τ{\barν}_τν_e\barν_e$, $e^+e^-\to μ^+μ^-ν_τ{\barν}_τν_μ\barν_μ$, $e^+e^-\to μ^+e^-ν_τ{\barν}_τν_μ\barν_e$, and $e^+e^-\to μ^-e^+ν_τ{\barν}_τν_e\barν_μ$ are also discussed for the case of unpolarized electron and positron beams. In the latter cases it is possible to measure $\mbox{Re}\,b$ using the differential cross section over momenta of both registered particles.

hep-ph↗
arXiv2022

Photoproduction of $e^+e^-$ pair in a Coulomb field near the threshold

We consider the electron-positron pair production by a photon in Coulomb field near threshold. We obtain the analytical results for the particle energy spectrum and angular distribution exactly in the parameter $Ze^2/\hbar v$. We show that Furry-Sommerfeld-Maue approximation for the wave functions used by Nishina, Tomonaga and Sakata is not sufficient and leads to wrong results.

hep-ph↗
arXiv2022

$N\bar{N}$ production in $e^{+}e^{-}$ annihilation near the threshold revisited

Production of $p\bar{p}$ and $n\bar{n}$ pairs in $e^{+}e^{-}$ annihilation near the threshold of the process is discussed with account for the new experimental data appeared recently. Since a significant part of these new data was obtained at energies noticeably exceeding the threshold, we also take into account the form factor describing the amplitude of $N\bar{N}$ pair production at small distances. The effective optical potential, which describes a sharp dependence of the $N\bar{N}$ production cross sections near the threshold, consists of the central potential for $S$ and $D$ waves and the tensor potential. These potentials differ for the states with isospin $I=0$ and $I=1$ of $N\bar{N}$ pair. The optical potential describes well $N\bar{N}$ scattering phases, the cross sections of $p\bar{p}$ and $n\bar{n}$ production in $e^{+}e^{-}$ annihilation near the threshold, the electromagnetic form factors $G_{E}$ and $G_{M}$ for protons and neutrons, as well as the cross sections of the processes $e^{+}e^{-}\to6π$ and $e^{+}e^{-}\to K^{+}K^{-}π^{+}π^{-}$.

hep-ph↗
arXiv2022

Bremsstrahlung on noble gases at low energies

A detailed analysis of the bremsstrahlung spectrum at nonrelativistic electron scattering on argon and xenon is carried out. It is shown that the approximate formulas widely used for the description of bremsstrahlung spectra lead to predictions that significantly differ from the exact results. In the limit when the photon frequency tends to zero, a rigorous proof of the relationship between the spectrum of the bremsstrahlung with a transport cross section of electron scattering on an atom is given. This proof does not require any assumptions about the dependence of the scattering phases on energy. For electron energies lower than the luminescence threshold, it is shown that the predictions for a number of radiated photons obtained by the exact formula are in good agreement with the available experimental data.

physics.atom-ph↗
arXiv2022

Effects of isospin violation in the $e^+e^- \rightarrow B^{(*)}\bar B^{(*)}$ cross sections

Model estimates are obtained for the influence of Coulomb effects on the ratio of the cross sections for the production of charged and neutral $B\bar B$ and $B^*\bar B^*$ pairs in $e^+e^-$ annihilation. It is shown that the difference between the masses of charged and neutral mesons obtained under the assumption that this ratio is constant on a scale of the order of the beam energy spread can differ from the true one by $δM \sim 0.03\,\mbox{MeV}$ at the energy of $Υ(5S)$ and by $δM \sim 0.4\,\mbox{MeV}$ at the energy of $Υ(4S)$. Thus, the errors given in the PDG for the difference between the masses of charged and neutral $B$ mesons, based on the results obtained at the energy of $Υ(4S)$, are strongly underestimated. Similar measurements at the energy of $Υ(5S)$ will have an order of magnitude smaller systematic shift for the mass difference. This circumstance should be taken into account when planning future experiments at the $B$ factory in KEK.

hep-ph↗
arXiv2022

Final-state interaction in the process $e^{+}e^{-}\rightarrowΛ_{c}\barΛ_{c}$

We show that the final-state interaction explains the nontrivial near-threshold energy dependence of the cross section of the process $e^{+}e^{-}\rightarrowΛ_{c}\barΛ_{c}$ observed by the Belle and BESIII collaborations. This energy dependence is the result of the mixture of $S$-wave and $D$-wave components of the $Λ_{c}\barΛ_{c}$ wave function due to a tensor interaction. The Coulomb potential is important only in the narrow energy region about a few MeV above the threshold of the process. It is shown that the widely used assumption that the impact of the Coulomb interaction on the cross sections of hadron production is reduced to the Sommerfeld-Gamow-Sakharov factor is not correct.

hep-ph↗
arXiv2021

Invariant-mass spectrum of $Λ\barΛ$ pair in the process $e^+e^-\rightarrowϕΛ\barΛ$

We show that the final-state interaction perfectly explains the recent experimental data of BESIII Collaboration on the near-threshold invariant-mass spectrum of $Λ\barΛ$ in the process $e^+e^-\rightarrowϕΛ\barΛ$. The position of peak in invariant-mass spectrum is above the threshold though the interaction of $Λ$ and $\barΛ$ is due to an attractive potential. This potential has a simple form and depends only on two parameters. We show that the invariant-mass spectrum is consistent with the quantum numbers $J^{PC}=1^{++}$ and $2^{++}$ of $Λ\barΛ$ pair but contradicts to $J^{PC}=2^{-+}$.

hep-ph↗
arXiv2021

Coulomb effects in the decays $Υ(4S) \rightarrow B\bar B$

A simple exactly solvable model is proposed for describing the decays $Υ(4S) \rightarrow B^0\bar B^0$ and $Υ(4S) \rightarrow B^+B^-$. Our predictions agree with available experimental data. Using this model, we analyze the Coulomb effects in the spectra of these decays. It is shown that the frequently used assumption of factorization of Coulomb effects is not fulfilled. The Coulomb interaction leads to the difference in the positions and heights of the peaks corresponding to the charged and neutral modes. As a result, the ratio of probability of $Υ(4S)\rightarrow B^+B^-$ decay and $Υ(4S) \rightarrow B^0\bar B^0$ decay is a nontrivial function of energy.

hep-ph↗
arXiv2021

Quadrupole radiation and $e^+e^-$ pair production in the collision of nonrelativistic nuclei

We analyze the one-photon mechanism of $e^+e^-$ pair production in the collision of nonrelativistic nuclei. The contribution of electric quadrupole radiation of virtual photon to the corresponding cross section is found. The effect of the finite nuclear size is considered in detail. A comparison is made with the contribution of electric dipole radiation of virtual photon and with the contribution of the two-photon pair production mechanism. It is shown that the contribution of electric quadrupole radiation is dominant in a wide range of relative velocities. The cross section for the production of $e^+e^-$ pair with the capture of an electron by one of the nuclei is also analyzed.

nucl-th↗
arXiv2021

Possible studies at the first stage of the NICA collider operation with polarized and unpolarized proton and deuteron beams

This paper contains suggestions for experiments with usage of the Spin Physics Detector (SPD) at the first stage of the SPD NICA Programme developing at JINR. Double polarized pp-, dd- and pd- collisions at c.m.s. NN energies of 3.4-10 GeV, which will be accessible at the initial stage of experiments, allow one to study spin dependence of the NN interaction, search for multiquark states at double strangeness, charm and beauty thresholds, study the short-range structure of the deuteron. Double polarized pd scattering offer a possibility to test the Standard Model through the search for T-invariance violation.

hep-ph↗
arXiv2020

Charge asymmetry in decays $ B\rightarrow D\bar DK$

We discusses the charge asymmetry in $ B\rightarrow D\bar DK$ decays with an invariant mass of the $D\bar D$ pair near the $Ψ(3770)$ resonance. Unlike $ Ψ(3770) $ decays in $ e^+e^- $ annihilation, in $B^+$ decays the probability of $D^0\bar D^0$ production is almost three times higher than $D^+ D^-$. In $B^0$ decays, the ratio of these probabilities will be opposite. The effect is explained by the fact that, in $B$ -meson decays, the $D\bar D$ pair is produced in a superposition of isoscalar and isovector states, and only in combination with $K$ -mesons the total state has $ 1/2 $ isospin. We present a simple model in which the interference of the nonresonant isovector amplitude with the resonant isoscalar amplitude explains the experimental data.

hep-ph↗
arXiv2020

Parity violation in proton-deuteron scattering

The effects of parity violation in the interaction of relativistic polarized protons and deuterons are discussed. Within Glauber's approach, estimates are obtained for P-odd asymmetries in the total and elastic scattering cross sections, in the deuteron dissociation cross section, and in the inelastic cross section with meson production in a final state. It is shown that, from the point of view of the magnitude of the P-odd effects, the interaction of polarized deuterons with unpolarized protons has an advantage over the interaction of polarized protons with unpolarized deuterons. A significant P-odd asymmetry was found in the dissociation channel of the polarized deuteron.

hep-ph↗
arXiv2020

Gauge invariance and amplitudes of two-photon processes

A method to derive the convenient representations for many two-photon amplitudes is suggested. It is based on the use of the gauge in which the photon propagator has only space components. The amplitudes obtained have no any strong numerical cancellations and, therefore, are very convenient for numerical evaluations. Our approach is illustrated by the consideration of the processes $e^+e^-\to e^+e^-e^+e^-$, $e^+e^-\rightarrow e^+e^-μ^+μ^-$, and $e^+e^-\to μ^+μ^-π^+π^-$. The method is extended on the case of polarized particles. The amplitudes obtained in this approach have been employed for extension of the event generator developed by F.A. Berends, P.H. Daverveldt, and R. Kleiss.

hep-ph↗
arXiv2020

Spin dynamics of a hydrogen atom in a periodic magnetic structure

The spin dynamics of a hydrogen atom during the passage of a periodic magnetic structure is discussed. The occupation numbers of the components of the hyperfine structure are considered as a function of time. The characteristic low-frequency oscillations are visible, which have a direct analogue in the effect of nuclear magnetic resonance. An envelope forms of these oscillations are found using the Krylov-Bogolyubov-Mitropol'skii method. The dependence of spin dynamics on the parameters of the magnetic structure is investigated. It is shown that this dependence is very sensitive to the structure of the magnetic field.

physics.atom-ph↗
arXiv2020

Parity violation in high-energy proton-proton scattering

A new approach is proposed to describe the parity violation in the process of scattering of a polarized proton by a proton at high energies. It is shown that in the tree approximation the P-odd amplitude of proton-proton scattering is substantially smaller than the P-odd amplitude in proton-neutron scattering. The main source of P-odd asymmetry in proton-proton scattering is radiative corrections due to the charge-exchange strong interaction. We predict that the asymmetry in the inelastic cross section is substantially less than the asymmetry in the elastic cross section.

hep-ph↗