S. I. Mishnev

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.

Internal polarized deuterium target with cryogenic atomic beam source

Abstract Description of the polarized deuterium gas target used at the VEPP-3 electron storage ring for experiments on elastic and inelastic ed scattering is given. Superconducting sextupole magnets with the pole tip magnetic field up to 4.8 T are used in atomic beam source (ABS) to focus atoms. The flux of polarized atoms injected into the storage cell was measured to be 8.2×10 16 at / s for deuterium and 7.9×10 16 at / s for hydrogen. The measured target thickness 8×10 13 at / cm 2 is consistent with the thickness calculated from the measured beam intensity. The effective tensor polarization of the deuterium target during the experiment was found to be P zz =0.397. Further improvements of the target and possible limitation of the beam intensity from ABS are discussed.

Application of Synchrotron Radiation for Studying Detonation and Shock-Wave Processes

A new method of remote investigation of detonation and shock‐wave processes with the use of synchrotron radiation is proposed. The facility used for the first experiments with measurement of density and small‐angle x‐ray scattering in detonation of condensed explosives is described. The high time and spatial resolution of the techniques proposed allows one to determine the character and mechanism of destruction of the condensed phase and the growth dynamics of new structures, including crystalline ones, in detonation flows. The capabilities of the new technique are described.

High precision measurement of the Ψ- and Ψ′-meson masses

Abstract A high precision measurement of the Ψ- and Ψ′-resonance masses has been performed at the new storage ring VEPP-4. The resonance depolarization method has been used for the absolute calibration of the beam energy. Application of this technique allowed improvement of the accuracy of the Ψ- and Ψ′-mass measurements by a factor of more than ten. The following mass values have been obtained: m Ψ = 3096.93 ± 0.09 MeV, m Ψ ′ = 3686.00 ± 0.10 MeV; the mass difference is thus m Ψ ′ − m Ψ = 589.07 ± 0.13 MeV.

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.

A high precision measurement of the ϒ, ϒ′ and ϒ″-meson masses

Abstract An experiment has been performed at the storage ring VEPP-4 using the MD-1 detector. The resonance depolarization method has been employed for the absolute calibration of the beam energy. This has allowed the accuracy of the mass measurement to be improved by a factor of ten. The following mass values of ϒ, ϒ′ and ϒ″ -mesons have been obtained: M ( ϒ )=9460.6±0.4 MeV, M ( ϒ ′)=10023.8±0.5 MeV, M ( ϒ ″)=10355.5±0.5 MeV.

Measurement of main parameters of the ψ(2S) resonance

A high-precision determination of the main parameters of th eψ(2S ) resonance has been performed with the KEDR detector at the VEPP-4Me+e− collider in three scans of the ψ(2S )–ψ(3770) energy range. Fitting the energy dependence of the mu ltihadron cross section in the vicinity of theψ(2S ) we obtainedthe mass value M = 3686.114± 0.007± 0.011 +0.002 −0.012 MeV and the product of the electron partial width by the branchin g fraction into hadrons Γee × Bh = 2.233± 0.015± 0.037± 0.020 keV. The third error quoted is an estimate of the model dependence of the result due to assumptions on the interference e ffects in the cross section of the single-photon e+e− annihilation to hadrons explicitly considered in this work . Implicitly, the same assumptions were employed to obtain the charmonium leptonic width and th e absolute branching fractions in many experiments. Usingthe result presented and the world average values of the electron and hadron branchin g fractions, one obtains the electron partial width and the total width of the ψ(2S ): Γee = 2.282± 0.015± 0.038± 0.021 keV, Γ = 296± 2± 8± 3 keV. These results are consistent with and more than two times mor e precise than any of the previous experiments.

Large impact parameter cut-off in the process e+e−→e+e−γ

Abstract In investigating the e + e − → e + e − γ process the radiation probability is oberved to be substantially less than that calculated in the standard QED. The effect is due to the fact that the characteristic impact parameters in the process are much greater than the transverse sizes of the colliding beams. The Compton scattering γ-spectrum of the synchrotron radiation by a colliding beam is measured.

Measurement of ψ(3770) parameters

Abstract We report the final results of a study of the ψ ( 3770 ) meson using a data sample collected with the KEDR detector at the VEPP-4M electron–positron collider. The data analysis takes into account interference between the resonant and nonresonant D D ¯ production, where the latter is related to the nonresonant part of the energy-dependent form factor F D . The vector dominance approach and several empirical parameterizations have been tried for the nonresonant F D N R ( s ) . Our results for the mass and total width of ψ ( 3770 ) are M = 3779.2 − 1.7 + 1.8 − 0.7 + 0.5 − 0.3 + 0.3 MeV , Γ = 24.9 − 4.0 + 4.6 − 0.6 + 0.5 − 0.9 + 0.2 MeV , where the first, second and third uncertainties are statistical, systematic and model, respectively. For the electron partial width two possible solutions have been found: ( 1 ) Γ e e = 154 − 58 + 79 − 9 + 17 − 25 + 13 eV , ( 2 ) Γ e e = 414 − 80 + 72 − 26 + 24 − 10 + 90 eV . Our statistics are insufficient to prefer one solution to another. The Solution (2) mitigates the problem of non- D D ¯ decays but is disfavored by potential models. It is shown that taking into account the resonance–continuum interference in the near-threshold region affects resonance parameters, thus the results presented cannot be directly compared with the corresponding PDG values obtained ignoring this effect.

Absolute calibration of particle energy at VEPP-4M

We have started a new series of experiments on a precise measurement of J/Ψ-, Ψ′- mesons and τ-lepton masses at VEPP-4M collider with KEDR detector. Features of the method used for an absolute particle energy calibration based on the resonance depolarization are described.