arXiv subjects

V. N. Stibunov

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

11 recordsLinked to original sources

arXiv2015

Measurement of the two-photon exchange contribution to the elastic $e^{\pm}p$ scattering cross sections at the VEPP-3 storage ring

The ratio of the elastic $e^+ p$ to $e^- p$ scattering cross sections has been measured precisely, allowing the determination of the two-photon exchange contribution to these processes. This neglected contribution is believed to be the cause of the discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. The experiment was performed at the VEPP-3 storage ring at beam energies of 1.6 and 1.0 GeV and at lepton scattering angles between $15^\circ$ and $105^\circ$. The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions.

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arXiv2011

Measurement of the two-photon exchange contribution in elastic $ep$ scattering at VEPP-3

We report on the status of the Novosibirsk experiment on a precision measurement of the ratio $R$ of the elastic $e^+ p$ and $e^- p$ scattering cross sections. Such measurements determine the two-photon exchange effect in elastic electron-proton scattering. The experiment is conducted at the VEPP-3 storage ring using a hydrogen internal gas target. The ratio $R$ is measured with a beam energy of 1.6 GeV (electron/positron scattering angles are $θ= 55 ÷75^{\circ}$ and $θ= 15 ÷25^{\circ}$) and 1 GeV ($θ= 65 ÷105^{\circ}$). We briefly describe the experimental method, paying special attention to the radiative corrections. Some preliminary results are presented.

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arXiv2007

Measurement of tensor analyzing powers in deuteron photodisintegration

New accurate measurement of tensor analyzing powers T20, T21 and T22 in deuteron photodisintegration has been performed. Wide-aperture non-magnetic detectors allowed to cover broad kinematic ranges in a single setup: photon energy = 25 to 600 MeV, proton emission angle in CM = 24 to 48 deg. and 70 to 102 deg. New data provide a significant improvement of a few existing measurements. The angular dependency of the tensor asymmetries in deuteron photodisintegration is extracted for the first time.

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arXiv2006

Incoherent pion photoproduction on the deuteron in the first resonance region

Incoherent pion photoproduction on the deuteron is studied in the first resonance region. The unpolarized cross section, the beam asymmetry, and the vector and tensor target asymmetries are calculated in the framework of a diagrammatic approach. Pole diagrams and one-loop diagrams with $NN$ scattering in the final state are taken into account. An elementary operator for pion photoproduction on the nucleon is taken in various on-shell forms and calculated using the SAID and MAID multipole analyses. Model dependence of the obtained results is discussed in some detail. A comparison with predictions of other works is given. Although a reasonable description of many available experimental data on the unpolarized total and differential cross sections and photon asymmetry has been achieved, in some cases a significant disagreement between the theory and experiment has been found. Invoking known information on the reactions $γd\toπ^0 d$ and $γd\to np$ we predict the total photoabsorption cross section for deuterium. We find that our values strongly overestimate experimental data in the vicinity of the $Δ$ peak.

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arXiv2004

Two-photon exchange and elastic scattering of electrons/positrons on the proton. (Proposal for an experiment at VEPP-3)

It has been suggested that two-photon exchange corrections could explain the discrepancy between Rosenbluth extractions of the proton form factors and recent polarization transfer measurements. We propose a precise comparison of electron-proton and positron-proton scattering at Q^2=1.6 GeV^2 to determine if two-photon exchange at moderate Q^2 values is in fact able to explain the discrepancy.

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arXiv2004

Tensor analyzing powers in forward angle exclusive $π$-meson photoproduction on deuteron

The target tensor analyzing powers of the process $γd -> π^{-}pp$ had been studied in the plane wave impulse approximation, if both ejected protons are detected in coincidence and in the directions, symmetrical respect to the incoming photon momentum, being in the proton plane. The matrix elements of the studied reaction become essentially simple, if the magnitudes of the proton momenta p1 = p2 = p are equal. That proton kinematics keeps the ejected pion angle near zero, therefore the one body pion production operator does not include the spin-non-flip term. Moreover, the transition to the triplet, spatially antisymmetric final pp- state is strongly suppressed from the symmetrical deuteron S - state as well as matrix elements have a large dependence from the orientation of the deuteron spin. The values of the $T_{22}(\vec p)$ component, calculated with three realistic deuteron wave functions in the proton momentum region p >= 350 MeV/c and proton polar angle theta >= 40 deg., differ one from another noticeably.

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arXiv2003

General Formulae of Invariant Functions of the Generalized Reaction γN - γN in the Effective Lagrangians Method

The crossed channels of generalized reaction γN - γN have been considered. The transformation coefficients from the independent helicity amplitudes to the invariant functions are calculated. The explicit expressions for invariant functions have been obtained with the subject to the contribution of Born diagrams in s-, u-, and t-channel and six resonances in s- and u-channel. It has been shown that the obtained invariant functions meet the requirements of crossing-symmetry.

nucl-th↗

arXiv2002

Reduction of the Bethe-Salpeter equation for the scattering amplitude of the particles with spin 1 to system of the integral equations for invariant functions

Bethe-Salpeter equation for the massive particles with spin 1 is considered. The scattering amplitude decomposition of the particles with spin 1 by relativistic tensors is derived. The transformation coefficients from helicity amplitudes to invariant functions is found. The integral equations system for invariant functions is obtained and partial decomposition of this system is performed. Equivalent system of the integral equation for the partial helicity amplitudes is presented.

hep-th↗

arXiv1999

The Reaction D(e,pp)e'pi- on Polarized Deuteron at High Proton Momenta

The differential cross section and target asymmetry components of the reaction D(e,pp)e'pi- on polarized deuteron were measured. The kinetic energies of the protons were measured within 55-180 MeV and 46-265 MeV. The polar acceptance angles in laboratory frame for the both protons are (64 - 82) degrees and the azimuthal angles are (-16 +16), (164 - 196) degrees. The sharp peak of the tensor a(20)-component of the target asymmetry is found near the invariant mass of the pppi-system M(pppi) = 2300 MeV/c**2. The performed calculations of the differential yield and the tensor target asymmetry do not describe the obtained experimental results.

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arXiv1999

Influence of the re-scattering process on polarization observables in reaction gamma + d --> p + p + pi- in Delta - resonance region

Influence of the effects of the pion-nucleon and nucleon-nucleon re-scattering on the polarization observables of the reaction gamma + d = p + p + pi- in Delta - isobar region is investigated. Pion-nucleon and nucleon-nucleon re-scattering are studied in the diagrammatic approach. Relativistic-invariant forms of the pion photoproduction and pion-nucleon scattering operators are used. The unitarization procedure in K-matrix approach is applied for the resonance partial amplitudes. It is shown a considerable influence of the re-scattering effects on the polarization observables of this reaction in the Delta - resonance region for the large momenta of the final protons.

hep-ph↗

arXiv1999

Contribution of the additional neutral pion production in the reaction d(e,pp)X

Recently, we have performed the experiment on studying the pion electroproduction at photon point on the internal polarized deuterium target at the VEPP-3 storage ring. For the more complete treatment of the reaction d(e,pp)X we investigate the reaction channel with an additional neutral pion production as background to the leading reaction of the single negative pion production. To study this background process we considered the nucleon pole mechanism and the two-body mechanism. In the latter mechanism a Delta(1232) and the pion are produced in one nucleon then the pion is absorbed by other nucleon producing just one more Delta (1232). The final proton-pion systems come from the decay of the both Deltas. In this work we have estimated the contribution of the reaction with additional neutral pion production into the whole yield for the different polarization states of the deuteron in the kinematic conditions of the VEPP-3 d(e,pp)X - experiment.

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