arXiv subjects

Yu. M. Bystritskiy

Publications and source records attributed to Yu. M. Bystritskiy.

44 records · Page 3Linked to original sources

arXiv2007

Comments to the calculation of transverse beam spin asymmetry for electron proton elastic scattering

The transverse beam spin induced asymmetry is calculated for the scattering of transversally polarized electrons on a proton target within a realistic model. Such asymmetry is due to the interference between the Born amplitude and the imaginary part of two photon exchange amplitude. In particular, the contribution of non-excited hadron state (elastic) to the two photon amplitude is calculated. The elastic contribution requires infrared divergences regularization and can be expressed in terms of numerical integrals of the target form factor. The inelastic channel corresponding to the one pion hadronic state contribution is enhanced by squared logarithmic terms. We show that the ratio of elastic over inelastic channel is of the order of 0.3 and cannot be ignored. Enhancement effects due to the decreasing of form factors bring the transverse beam asymmetry to values as large as $10^{-4}$ for particular kinematical conditions.

hep-ph↗

arXiv2006

Measuring C-odd correlations at lepton-proton and photon-proton collisions

We consider the charge-odd correlations (COC) in cross sections of processes of production of charged particles. The cases of a muonic pair and pion systems $π^{+}π^{-},π^{+}π^{-}π^{0}$ are considered in detail for electron-proton or photon-proton collisions in the proton fragmentation region kinematics. COC arise from interference of amplitudes which describe the different mechanisms of charged leptons (pions) creation. One of them corresponds to production of particles in the charge-odd state (one virtual photon or vector meson annihilation to this system of particles) and the other corresponds to the charge-even state of produced particles (creation by two photons). COC for muon-antimuon pair creation have a pure QED nature and can be considered as a normalization process. The processes with pion production are sensitive to some characteristics of proton wave functions and, besides, can be used for checking the anomalous and normal parts of the effective pionic lagrangian. Three electromagnetic currents operator matrix element can be measured in photon-proton interactions with lepton pair production. For this aim a charge-odd combination of cross sections can be constructed as a conversion of leptonic 3-rank tensor with hadronic ones. These experiments can be considered as an alternative to deep virtual Compton scattering.

hep-ph↗

arXiv2006

The structure function method applied to polarized and unpolarized electron-proton scattering: a solution of the G_E(p)/G_M(p) discrepancy

The cross section for polarized and unpolarized electron-proton scattering is calculated taking into account radiative corrections in leading and next-to leading logarithmic approximation. The expression of the cross section is formally similar to the cross section of the Drell-Yan process, where the structure functions of the electron play the role of Drell-Yan probability distributions. The interference of the Born amplitude with the two photon exchange amplitude (box-type diagrams) is expressed as a contribution to K-factor and it is larger when the momentum is equally shared between the two photons, assuming that proton form factors decrease rapidly with the momentum transfer squared. The calculation of the box amplitude is done when the intermediate state is a proton or the Delta-resonance. The results of numerical estimations show that the present calculation of radiative corrections can bring into agreement the conflicting experimental results on proton electromagnetic form factors an that the two photon contribution is very small.

hep-ph↗

arXiv2006

New formulation of (g-2)_μhadronic contribution

In frames of agreement to consider the annihilation of electron-positron pair to hadrons cross section to be including the virtual photon polarization effects a new formulation of hadron contribution to muon anomalous magnetic moment is suggested. It consists in using the experimentally observed cross section converted with the known kernels. The lowest order kernel remains to be the same but some modification of radiative corrected kernel is needed. The explicit form of this new kernel is given. We estimate the accuracy of new formulation on the level δa^{hadr}_μ/a^{hadr}_μ\sim 10^{-5}.

hep-ph↗

arXiv2006

Target normal spin asymmetry and charge asymmetry for $eμ$ elastic scattering and the crossed processes

Two kinds of asymmetry arise from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photons exchange, namely charge-odd and one spin asymmetries. In case of unpolarized particles the charge-odd correlation is calculated. It can be measured in combination of electron muon and positron muon scattering experiments. The forward-backward asymmetry is the corresponding quantity which can be measured for the crossed processes. In the case of polarized muon the one-spin asymmetry for annihilation and scattering channels has been calculated. The additional structure function arising from the interference is shown to suffer from infrared divergencies. The background due to electroweak interaction is discussed.

hep-ph↗

arXiv2005

Process e^+ e^- \to 3π(γ) with final state radiative corrections

We consider the process of annihilation of e^+ e^- to three pion final state for the case of moderately high energies. The final state emission of virtual and real photon is considered explicitly. The calculations are performed in frames of QED with point-like mesons and pion part of chiral perturbation theory. Some numerical estimates are given.

hep-ph↗

arXiv2005

Quark loop contribution to π^0 \to 4γ

We find the contribution of constituent quark loop mechanism to the branching ratio B_{4γ} = Γ_{4γ}/Γ_{4γ} \sim 5.45 \cdot 10^{-16} for the reasonable choice of constituent quark mass m \sim 280 MeV. This result is in agreement with vector-dominance approach result obtained years ago. Thus the main contribution arises from QED mechanism π^0 \to γ(γ^*) \to γ(3γ) including light-light scattering block with electron loop. This contribution was investigated in paper of one of us and gave B_{4γ} \sim 2.6 \cdot 10^{-11}.

hep-ph↗

arXiv2005

The cross sections of the muons and charged pions pairs production at electron-positron annihilation near the threshold

The processes of muons (tau) and charged pions pairs production at electron-positron annihilation with first order radiative corrections are considered. The calculation results are presented assuming the energies of final particles (cms implied) to be not far significantly from threshold production. The invariant mass distributions for the muon (tau) and pion pairs are obtained both for the initial and final state radiation. Some analytical calculations are illustrated numerically. The pions were assumed to be point-like objects and scalar QED was applied for calculation. The QED radiative corrections related to the final state radiation, additional to the well known Coulomb factor, are treated near threshold region exactly.

hep-ph↗