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A. G. Shamov

Publications and source records attributed to A. G. Shamov.

30 records · Page 2Linked to original sources
arXiv2011

Measurement of J/psi leptonic width with the KEDR detector

We report a new precise determination of the leptonic widths of the J/psi meson performed with the KEDR detector at the VEPP-4M $e^{+}e^{-}$ collider. The measured values of the J/psi parameters are: Γ_{ee}\timesΓ_{ee}/Γ= 0.3323 \pm 0.0064 (stat.) \pm 0.0048 (syst.) keV Γ_{ee}\timesΓ_{μμ}/Γ=0.3318 \pm 0.0052 (stat.) \pm 0.0063 (syst.) keV. Assuming $eμ$ universality and using the table value of the branching ratios the leptonic Γ_{ll}= 5.59 \pm 0.12 keV width and the total Γ=94.1 \pm 2.7 keV widths were obtained. We also discuss in detail a method to calculate radiative corrections at a narrow resonance.

hep-ex↗
arXiv2011

The beam energy measurement system for the Beijing electron-positron collider

The beam energy measurement system (BEMS) for the upgraded Beijing electron-positron collider BEPC-II is described. The system is based on measuring the energies of Compton back-scattered photons. The relative systematic uncertainty of the electron and positron beam energy determination is estimated as 2 \cdot 10^{-5}. The relative uncertainty of the beam's energy spread is about 6 %.

physics.acc-ph↗
arXiv2010

Measurement of B(J/psi->eta_c gamma) at KEDR

We present a study of the inclusive photon spectrum from 6.3 million J/psi decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/psi -> eta_c gamma, eta_c width and mass. Taking into account an asymmetric photon line shape we obtain: M(eta_c) = (2978.1 +- 1.4 +- 2.0) MeV/c^2, Gamma(eta_c) = (43.5 +- 5.4 +- 15.8) MeV, B(J/psi->eta_c gamma) = (2.59 +- 0.16 +- 0.31)%$.

hep-ex↗
arXiv2010

Measurement of J/psi to eta_c gamma at KEDR

We present a study of the inclusive photon spectra from 5.9 million J/psi decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of radiative decay J/psi to eta_c gamma, eta_c width and mass. Our preliminary results are: M(eta_c) = 2979.4+-1.5+-1.9 MeV, G(eta_c) = 27.8+-5.1+-3.3 MeV, B(J/psi to eta_c gamma) = (2.34+-0.15+-0.40)%.

hep-ex↗
arXiv2010

Measurement of Γ_{ee}(J/ψ)*Br(J/ψ->e^+e^-) and Γ_{ee}(J/ψ)*Br(J/ψ->μ^+μ^-)

The products of the electron width of the J/ψmeson and the branching fraction of its decays to the lepton pairs were measured using data from the KEDR experiment at the VEPP-4M electron-positron collider. The results are Γ_{ee}(J/ψ)*Br(J/ψ->e^+e^-)=(0.3323\pm0.0064\pm0.0048) keV, Γ_{ee}(J/ψ)*Br(J/ψ->μ^+μ^-)=(0.3318\pm0.0052\pm0.0063) keV. Their combinations Γ_{ee}\times(Γ_{ee}+Γ_{μμ})/Γ=(0.6641\pm0.0082\pm0.0100) keV, Γ_{ee}/Γ_{μμ}=1.002\pm0.021\pm0.013 can be used to improve theaccuracy of the leptonic and full widths and test leptonic universality. Assuming eμuniversality and using the world average value of the lepton branching fraction, we also determine the leptonic Γ_{ll}=5.59\pm0.12 keV and total Γ=94.1\pm2.7 keV widths of the J/ψmeson.

hep-ex↗
arXiv2010

Recent results from the KEDR Detector

We report results of experiments performed with the KEDR detector at the VEPP-4M e+e- collider. They include precise measurement of the D0 and D+- meson masses, determination of the psi(3770) resonance parameters, and a search for narrow resonances in e+e- annihilation at center-of-mass energies between 1.85 and 3.1 GeV.

hep-ex↗
arXiv2002

Precision luminosity measurement at LHC using two-photon production of mu^+ mu^- pairs

The application of the two-photon process pp -> pp + mu^+mu^- for the luminosity measurements at LHC with the ATLAS detector is considered. The expected accuracy of the absolute offline luminosity determination is 1 - 2 % for the luminosity range of 10^{33} - 10^{34} cm^-2 s^-1. The preliminary cross section estimates done for LHCb promise the same level of the luminosity measurement accuracy at L = 2 x 10^{32} cm^-2 s^-1.

hep-ex↗
arXiv2001

Experimental investigation of high-energy photon splitting in atomic fields

The new data analysis of the experiment, where the photon splitting in the atomic fields has been observed for the first time, is presented. This experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, the statistics of $1.6\cdot 10^9$ photons incident on the BGO target was collected. About 400 candidates to the photon splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the cross section calculated exactly in an atomic field. The predictions obtained in the Born approximation significantly differ from the experimental results.

hep-ex↗
arXiv1998

Delbrück scattering at energies 140 - 450 MeV

The differential cross section of Delbrück scattering is measured on a bismuth germanate $Bi_4Ge_3O_{12}$ target at photon energies $140 - 450 MeV$ and scattering angles $2.6 - 16.6 mrad$. A good agreement with the theoretical results, obtained exactly in a Coulomb field, is found.

hep-ex↗