D. K. Toporkov

Measurement of the Two-Photon Exchange Contribution to the Elastic e ± 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° and 105°. The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions.

A new event generator for the elastic scattering of charged leptons on protons

This paper describes a new multipurpose event generator, ESEPP, which has been developed for the Monte Carlo simulation of unpolarized elastic scattering of charged leptons on protons. The generator takes into account the lowest-order QED radiative corrections to the Rosenbluth cross section including first-order bremsstrahlung without using the soft-photon or ultrarelativistic approximations. ESEPP can be useful for several significant ongoing and planned experiments.

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 ° and θ = 15 ÷ 25 ° ) and 1 GeV ( θ = 65 ÷ 105 ° ). We briefly describe the experimental method, paying special attention to the radiative corrections. Some preliminary results are presented.

Tensor observables in electro- and photoreactions on the deuteron

The study of polarization effects in reactions with a simplest nucleus, deuteron, plays an important role for the investigation of deuteron structure as well as for the research of the properties of the strong interaction. However, data on the tensor observables in the electro- and photoreactions with deuteron appeared not so long ago. We present here a brief overview of the experiments on three such reactions with a deuteron: elastic scattering, photodisintegration and coherent photoproduction of the neutral pion.

Photoreactions with tensor-polarized deuterium target at VEPP–3

We give an overview of the activity in studying photoprocesses on a tensor-polarized deuterium target, which is carried out at the VEPP–3 electron storage ring. Recent experimental results on tensor asymmetries in two-body deuteron photodisintegration at the photon energy up to 500 MeV, and in coherent pion photoproduction on deuteron are presented. Plans to upgrade the facility and future experiments are discussed. Further progress is connected with the installation of a tagging system for almost-real photons. This would allow us to extend the measurements of polarization observables in photonuclear reactions on deuteron up to a photon energy of 1.5 GeV and permit to perform double polarized experiments – with linear polarized photon beams and tensor/vector polarized deuterium targets.

Polarization of Molecules: What We Can Learn from the Nuclear Physics Efforts?

The progress in the field of thermonuclear fusion in the last years is very impressive. Lately, intensive discussions are concentrated on the application of polarized fuel for fusion, in order to maximize the efficiency of nuclear fuel utilization. At the moment the only sources of polarized hydrogen isotopes are sources of polarized atoms created for the use of nuclear physics experiments. The intensity of the best sources of polarized beams is less then \(10^{17}\) atoms \(\mathrm{s}^{-1}\) and limited by intrabeam scattering. This intensity is certainly not enough for tokamak reactor which requires at least \(10^{21}\) atoms \(\mathrm{s}^{-1}\). Here we discuss the possibility to obtain nuclear spin polarized molecules of hydrogen isotopes by their separation in a nonuniform magnetic field. Using the sources of molecules with large area it seems possible to overcome the limitations associated with intrabeam scattering and to obtain beams of polarized molecules of greater intensity in comparison with the atomic beam sources.

Two-photon exchange contribution to elastic electron–proton scattering: measurements at the VEPP-3 storage ring

A striking discrepancy between the results for the ratio of electric and magnetic form factors of the proton obtained by two approaches: the Rosenbluth extraction from the unpolarized cross section and the double-polarization measurements has led to a serious re-examination of the role played by two-photon exchange diagrams. The evaluation of such diagrams could not be done in model-independent way, which means an experimental verification is required. One of the direct ways to do this is to measure the ratio of positron–proton and electron–proton elastic scattering cross-sections for identical kinematics. Such a measurement has been performed at the VEPP-3 storage ring at Novosibirsk. There were two runs at beam energies of 1.6 and 1.0 GeV at several ranges of scattering angle. The measurements covered the transferred momentum Q2 up to 1.5 GeV2 and the virtual photon polarization parameter down to 0.2 . The VEPP-3 experimental approach is described and the results of the measurements are presented.

Beam energy measurements for an experiment on elastic e±p scattering at the VEPP-3 storage ring

A precise comparison of the cross sections for the elastic scattering of electrons and positrons on protons was performed recently at the VEPP-3 storage ring in Novosibirsk, Russia. To provide the proposed accuracy, the energies of the electron and positron beams used during the experiment needed to be carefully maintained. This paper describes the special beam energy measurement system used in this experiment. This system is based on measuring the maximum energy of laser photons backscattered from electron and positron beams. It provides continuous beam energy measurements with a total relative uncertainty of less than 4.410−5.