L. M. Barkov

Measurement of tensor analyzing powers in deuteron photodisintegration

A new accurate measurement of the tensor analyzing powers T20, T21, and T22 in deuteron photodisintegration has been performed. Wide-aperture nonmagnetic detectors allowed broad kinematic coverage in a single set up: E(gamma)=25 to 600 MeV, and theta(p)(cm)=24 degrees to 48 degrees and 70 degrees to 102 degrees . The new data provide a significant improvement over the few existing measurements. The angular dependency of the tensor asymmetries in deuteron photodisintegration is extracted for the first time.

Experiments with internal targets at the VEPP-3 electron storage ring

An 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 Q2 = 8−15 fm−2 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 Eγ = 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.

Measurement of the tensor analyzing power components in the coherent photoproduction of a π0 meson on a deuteron

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.

Tensor asymmetry of π−-meson photoproduction on polarized deuterons

The tensor asymmetry of exclusive π−-meson photoproduction on polarized deuterons was investigated. The T20 and T22 components of the reaction analyzing power contribute to the measured asymmetry. The detector made it possible to record two outgoing protons in coincidence in the range of polar angles θ1,2 = 44° − 88° and in the momentum range p1,2 = 350 − 700 MeV c−1. The measurements were performed at the VEPP-3 storage ring (Novosibirsk) using an internal target. The experimental results are compared with theoretical calculations.

Proton form factors and two-photon exchange in elastic electron-proton scattering

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 θe = 15°–25° and 55°–75° in the first case and in the range of θe = 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.

Two-photon exchange and elastic scattering of positrons/electrons on the proton

D. M. Nikolenko∗,a J. Arrington,b L. M. Barkov,a V. F. Dmitriev,a,c V. V. Gauzshteyn,d R. A. Golovin,a,c A. V. Gramolin,a R. J. Holt,b V. V. Kaminsky,a B. A. Lazarenko,a S. I. Mishnev,a N. Yu. Muchnoi,a,c V. V. Neufeld,a A. V. Osipov†,d I. A. Rachek,a R. Sh. Sadykov,a Yu. V. Shestakov,a,c V. N. Stibunov,d D. K. Toporkov,a,c H. de Vries,e S. A. Zevakov a and V. N. Zhilich a aBudker Institute of Nuclear Physics, Novosibirsk, Russia bArgonne National Laboratory, Argonne, USA cNovosibirsk State University, Novosibirsk, Russia dNuclear Physics Institute of Tomsk Polytechnic University, Tomsk, Russia eNIKHEF, Amsterdam, The Netherlands

Search for the ϕ → π + π − γγ and ϕ → π + π − η decays with the CMD-2 detector

The ϕ → π+π−γγ and ϕ → π+π−η decays are sought in the experimental data obtained with the CMD-2 detector in the region of the ϕ-meson resonance. Upper limits ℛ(ϕ → ππγγ)< 1.2 × 10−4 and ℛ(ϕ → ππη) < 6.1 × 10−5 (both at a C.L. of 90%) are determined for the branching ratios of these decays.

Measurement of analyzing power T20 in elastic electron-deuteron scattering in the momentum transfer range of 0.3–0.8 (GeV/c)2

The results on the measurement of the analyzing power component T20 in elastic ed scattering are presented. An internal storage cell target technique was used in the VEPP-3 electron ring in Novosibirsk for this measurement. The measurement has been performed in the range of momentum transfer poorly investigated but important from theoretical point of view because of the node of the monopole charge form factor of the deuteron. The comparison of the other experimental data and some theories are discussed.