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.
VEPP-4 is a multipurpose storage ring facility at Budker Institute of Nuclear Physics (Novosibirsk, Russia) with several research programs including high energy physics in colliding beam mode, ...nuclear physics, synchrotron radiation, accelerator physics study, etc. The paper discusses VEPP-4 activities relating to generation and application of synchrotron radiation not only for SR user community but for beam diagnostics in storage ring as well.
We propose an experiment to search for a new gauge boson A' in e+e− annihilation by means of a positron beam incident on a gas hydrogen target internal to the bypass at the VEPP-3 storage ring. The ...search method is based on a missing mass spectrum in the reaction e+e−→γA'. It allows observation of the A' signal independently of its decay modes and life time. The projected result of this experiment corresponds to an upper limit on the square of the coupling constant ϵ2=3ċ10−8 with a signal-to-noise ratio of two to one at an A' mass of 5–20 MeV .
We present experimental results for T20 component of the tensor analyzing power for incoherent π− photoproduction on a deuteron. The experiment was performed on an internal tensor-polarized gas ...deuterium target of the VEPP-3 electron storage ring in 2021 using the proton-proton coincidence method. The data are compared with the results of numerical simulation.
Three components of the tensor analyzing power of the exclusive π− meson photoproduction on a deuteron, γd→ppπ−, are measured simultaneously for the photon energy range (300–900) MeV, detecting a ...pair of protons in the energy range (50–200) MeV. The experiment made use of an internal tensor-polarized deuterium gas target of the VEPP-3 electron storage ring and the two-proton coincidence recording method. The results obtained are compared with theoretical predictions within the framework of the diagrammatic approach.
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The paper presents results of a double polarization experiment to extract an asymmetry of the
π
-
-meson photoproduction on a tensor-polarized deuteron by a linearly polarized photon. The energy of ...photons lies in the range (300-700) MeV. The measurements were performed on the internal tensor-polarized deuterium target in the VEPP-3 electron-positron storage ring for the electron beam energy equal to 2 GeV. In the experiment, two protons and a scattered electron were detected in coincidence. The results of the measurement are compared with theoretical predictions made in the framework of impulse approximation, taking into account the
π
N
and
NN
-rescattering in the final state.
We present the first accurate results of measurements of the tensor analyzing power component
T
20
for the coherent neutral pion photoproduction on the deuteron. The measurements were performed at ...the Budker Institute of Nuclear Physics at VEPP-3 storage ring using the internal tensor polarized deuterium target. The measurements cover the region of photon energy from 200 to 450 MeV and the region of the center-of-mass pion polar angle from 100 to 140 degrees. The results obtained are compared with predictions of several theoretical models.
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 DD¯ production, where the latter is related to the nonresonant part of the energy-dependent form factor FD. The vector dominance approach and several empirical parameterizations have been tried for the nonresonant FDNR(s).
Our results for the mass and total width of ψ(3770) areM=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)Γee=154−58+79−9+17−25+13 eV,(2)Γee=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-DD¯ 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.
A high-precision determination of the main parameters of the ψ(2S) resonance has been performed with the KEDR detector at the VEPP-4M e+e− collider in three scans of the ψ(2S)–ψ(3770) energy range. ...Fitting the energy dependence of the multihadron cross section in the vicinity of the ψ(2S) we obtained the mass valueM=3686.114±0.007±0.011−0.012+0.002 MeV and the product of the electron partial width by the branching fraction into hadronsΓee×Bh=2.233±0.015±0.037±0.020 keV. The first and second uncertainties are statistical and systematic, respectively. The third uncertainty quoted is an estimate of the model dependence of the result due to assumptions on the interference effects 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 the absolute branching fractions in many experiments.
Using the result presented and the world average values of the electron and hadron branching 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 more precise than any of the previous experiments.
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