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E. A. Kuraev

Publications and source records attributed to E. A. Kuraev.

At least 91 records · Page 5Linked to original sources
arXiv2007

To a question on the η\to π^0 γγdecay width in meson-baryon chiral model

It is shown in the work of one of the authors in 1979 (MKV) that the contribution to the amplitude of this decay from diagrams with one baryon loop is equal to zero and contributions from diagrams with meson loops appear very small. However, pole diagrams with intermediate vector mesons were not considered there. Here it is shown that contributions of these pole diagrams dominate. The meson-baryon chiral model used here is compared with known quark chiral models. The obtained results are in satisfactory agreement with recent experimental data.

hep-ph↗
arXiv2007

Bremsstrahlung photon polarization for $ee^\pm\to (eγ)e^\pm$, and $ep\to (eγ)p$ high energy collisions

The polarization of bremsstrahlung photon in the processes $ee^\pm\to (eγ)e^\pm$, and $ep\to (eγ)p$ is calculated for peripheral kinematics, in the high energy limit where the cross section does not decrease with the incident energy. When the initial electron is unpolarized(longitudinally polarized) the final photon can be linearly (circularly) polarized. The Stokes parameters of the photon polarization are calculated as a function of the kinematical variables of process: the energy of recoil particle, the energy fraction of scattered electron, and the polar and azimuthal angles of photon. Numerical results are given in form of tables, for typical values of the relevant kinematic variables.

hep-ph↗
arXiv2007

QED processes in peripheral kinematics at polarized photon-photon and photon-electron colliders

The calibration QED process cross sections for experiments on planned electron-photon and photon-photon colliders for detecting the small angles scattered particles are calculated. These processes describe the creation of two jets moving sufficiently close to the beam axis directions. The jets containing two and three particles including charged leptons, photons and pseudoscalar mesons are considered explicitly. Considering the pair production subprocesses we take into account both bremsstrahlung and double photon mechanisms. The obtained results are suitable for further numerical calculations.

hep-ph↗
arXiv2007

Study of resonant processes for multi-pion production in $\bar p +p\to\ell ^++\ell^- +n_ππ$ annihilation

In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study multi-pion production in antiproton nucleon collisions. The main interest of this reaction is related to the possibility to study the properties of the presumable $\bar N N$ atom and of its resonances. For the case of formation of a scalar or pseudoscalar resonant state, with $I^G(J^{P})=1^-(0^{\pm}),~0^+(0^-)$ numerical results are obtained. The differential cross section in an experimental set-up where the pions invariant mass is measured, is given with explicit dependence on the lepton pair and pions invariant mass.

hep-ph↗
arXiv2007

Table of integrals. Asymptotical expressions for non--collinear kinematics

We present a set of Feynman integrals appearing in calculations of different QED processes to the one-loop accuracy. We consider scalar, vector, and tensor integrals with two, three, four and five denominators. The cases of equal and different fermion masses are considered. Results obtained are valid in the region where all kinematical invariants are large compared to the masses squared. Mass corrections for some scalar integrals in the case of different fermion masses are also given.

hep-ph↗
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↗
arXiv2007

Ground state $1/2^+$ octet baryon sum rules predicting a chain of inequalities for hadron photoproduction total cross-sections on corresponding baryons

Sum rules are derived relating Dirac mean square radii and anomalous magnetic moments of various couples of the ground state $1/2^+$ octet baryons with the convergent integral of the difference of hadron photoproduction cross-sections on the corresponding baryons. Taking into account the present knowledge of static parameters of baryons a chain of inequalities for total hadronic photoproduction cross-sections on baryons is found from those sum rules.

hep-ph↗
arXiv2006

Charge asymmetry for electron (positron)-proton elastic scattering

Charge asymmetry in electron (positron) scattering arises from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photons exchange. It can be extracted from electron proton and positron proton scattering experiments, in the same kinematical conditions. Considering the virtual photon Compton scattering tensor, which contributes to the box-type amplitude, we separate proton and inelastic contributions in the intermediate state and parametrize the proton form-factors as the sum of a pure QED term and a strong interaction term. Arguments, based on analyticity, are given in favor of cancellation of contributions from proton strong interaction form factors and of inelastic intermediate states in the box type amplitudes. In frame of this model, and assuming a dipole character of form-factors, numerical estimations are given for moderately high energies.

hep-ph↗
arXiv2006

Recoil proton distribution in high energy photoproduction processes

For high energy linearly polarized photon--proton scattering we have calculated the azimuthal and polar angle distributions in inclusive on recoil proton experimental setup. We have taken into account the production of lepton and pseudoscalar meson charged pairs. The typical values of cross sections are of order of hundreds of picobarn. The size of polarization effects are of order of several percents. The results are generalized for the case of electroproduction processes on the proton at rest and for high energy proton production process on resting proton.

hep-ph↗
arXiv2006

Testing axial and electromagnetic nucleon form factors in time-like regions in the processes $\bar p + n\to π^- +\ell^-+\ell^+$ and $\bar p+ p\to π^0 +\ell^- + \ell^+$, $\ell=e$, $μ$

In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study the annihilation channel in antiproton nucleon collisions with production of a single charged or neutral pion and a lepton-antilepton pair. These reactions allow to access nucleon and axial electromagnetic form factors in time-like region and offer a unique possibility to study the kinematical region below two nucleon threshold. The differential cross section in an experimental set-up where the pion is fully detected is given with explicit dependence on the relevant nucleon form factors. The possibility to measure heavy charged pion in the annihilation channel is also discussed.

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

Exclusive and inclusive muon pair production in collisions of relativistic nuclei

The exclusive production of one $μ^+μ^-$ pair in collisions of two ultra-relativistic nuclei is considered. We present a simple method for the calculation of the Born cross section for this process based on an improved equivalent photon approximation. We find that the Coulomb corrections to this cross section (corresponding to multi-photon exchange of the produced $μ^{\pm}$ with the nuclei) are small while the unitarity corrections (corresponding to the exchange of light-by-light blocks between nuclei) are large. This is in sharp contrast to the exclusive $e^+e^-$ pair production where the Coulomb corrections to the Born cross section are large while the unitarity corrections are small. We calculate also the cross section for the production of one $μ^+μ^-$ pair and several $e^+e^-$ pairs in the leading logarithmic approximation. Using this cross section we find that the inclusive production of $μ^+μ^-$ pair coincides in this approximation with its Born value.

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↗
arXiv2006

Radiative corrections to chiral amplitudes in quasiperipheral kinematics

Chiral amplitudes for two jets processes in quasi-peripheral kinematics are calculated at the Born and one loop correction level. The amplitudes of subprocesses describing interaction of virtual and real photon with creation of a charged fermion pair for various chiral states are considered in details. Similar results are presented for Compton subprocess with virtual photon. Contribution of emission of virtual, soft, and hard real additional photons are taken into account explicitly. The relevant cross sections expressed in terms of impact factors are in agreement with structure function approach in the leading logarithmical approximation. Contributions of the next to leading terms are presented in an analytical form. Accuracy estimation is discussed.

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