Search

The crossed channels of generalized γN → γN reactions are considered. The coefficients in the transformation from independent helicity amplitudes to invariant functions are calculated. Explicit expressions for the invariant functions are derived with allowance for the contribution from the Born diagrams in the s, u, and t channels and the diagrams for six resonances in the s and u channels. It is shown that the calculated invariant functions satisfy the crossing-symmetry requirements.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The effect of pion-nucleon and nucleon-nucleon rescatterings on polarization observables of the reaction γd → ppπ[sup -] are calculated in the delta-isobar region. Pion-nucleon and nucleon-nucleon rescatterings are considered on the basis of a diagrammatic approach. Lorentz invariant expressions are used for the operators of photoproduction and of pion scattering on a free nucleon. A unitarization procedure in the K-matrix approximation is used for resonance partial-wave amplitudes. It is shown that, in the delta-resonance region, rescattering has a sizable effect on polarization observables of the reaction γd → ppπ[sup -] at high momenta of final protons. [ABSTRACT FROM AUTHOR]

Proton electromagnetic form factors are among the most important sources of information about the internal structure of the proton. Two different methods for measuring these form factors, the method proposed by Rosenbluth and the polarization-transfer method, yield contradictory results. It is assumed that this contradiction can be removed upon taking into account the hard part of the contribution of two-photon exchange to the cross section for elastic electron-proton scattering. This contribution can measured experimentally via a precision comparison of the cross sections for the elastic scattering of positrons and electrons on protons. Such a measurement, performed at the VEPP-3 storage ring in Novosibirsk at the beam energies of 1.6 and 1.0 GeV for positron (electron) scattering angles in the ranges of θ = 15°-25° and 55°-75° in the first case and in the range of θ = 65°-105° in the second case is described in the present article. Preliminary results of this experiment and their comparison with theoretical predictions are described. [ABSTRACT FROM AUTHOR]

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° and 105°. The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions. [ABSTRACT FROM AUTHOR]

Results obtained by measuring three components of the tensor analyzing power in the reaction of π -meson photoproduction on a deuteron at final-proton momenta between 300 and 700 MeV/ c are presented. The measurements in question were performed at the VEPP-3 storage ring by using its internal deuterium-gas target featuring a tensor polarization with the aid of detection of two protons in coincidence. The experimental results obtained in this way are compared with their counterparts calculated theoretically. [ABSTRACT FROM AUTHOR]

Experimental differential cross sections of photoproduction of negative pions on a deuteron have been obtained as functions of the polar angle of emission of π mesons. A comparison is made of the measured cross sections with the results of calculations in a model that takes account the interaction in the final state of the reaction. [ABSTRACT FROM AUTHOR]

spectrum of virtual photons is analyzed in the reaction of electroproduction of negative pions on a deuteron when both finite protons are registered and their escape energies and angles are determined. [ABSTRACT FROM AUTHOR]

n overview of the recently completed, current, and planned experiments with internal targets at the VEPP-3 electron-positron storage ring in Novosibirsk is given. The results of the experiment to separately measure the deuteron form factors in elastic ed scattering in the range of momentum transfer Q = 8−15 fm are provided. The results of measuring the tensor analyzing power components of the tensor-polarized deuteron photodisintegration reaction in the range of γ-quantum energies E = 25−600 MeV are presented. The tensor analyzing powers of the coherent photoproduction of a neutral pion on a tensor-polarized deuteron have been measured for the first time. The almost-real photon tagging system being created is discussed. The status of the experiment under way to determine the contribution of two-photon exchange to the elastic ep scattering cross section is described. [ABSTRACT FROM AUTHOR]

The components of the tensor analyzing powers, T20, T21, and T22, of the coherent photoproduction of a π0 meson on a deuteron have been measured for photon energies of 250–450 MeV and pion emission angles of 90°–145°. The results are compared with the theoretical predictions. [ABSTRACT FROM AUTHOR]

The differential cross section of the reaction D(e,pp)e'π[sup -] is measured in the range of proton momenta 300-720 MeV/c and proton emergence angles 64-83° for invariant masses of the pp system ranging from 2m[sub p] to 2220 MeV/c². The measured values of the cross section are found to differ substantially from single-particle model calculations. The components of the analyzing power for this reaction are measured. [ABSTRACT FROM AUTHOR]