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N. Yu. Muchnoi

Publications and source records attributed to N. Yu. Muchnoi.

50 records · Page 3Linked to original sources
arXiv2012

Backscattering of Laser Radiation on Ultra-Relativistic Electrons in Transverse Magnetic Field: Evidence of Photon Interference in a MeV Scale

The experiment on laser light backscattering on relativistic electrons was carried out at the VEPP-2000 collider. Laser radiation (λ0 10.6 μm) was scattered head-on the 990 MeV electrons inside the dipole magnet, where an electron orbit radius is about 140 cm. The energies of backscattered photons were measured by the HPGe detector. It was observed experimentally that due to the presence of magnetic field, energy spectrum of backscattered photons differs from the Klein-Nishina cross section. The explanation of the effect is proposed in terms of classical electrodynamics. Moreover, it appears that the exact QED predictions for the phenomenon were done more than 40 years ago.

physics.acc-ph↗
arXiv2012

Measurement of ψ(3770) parameters

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 the interference between the resonant and nonresonant $D\bar{D}$ 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 $F_D^{\NR}(s)$. Our results for the mass and total width of ψ(3770) are M = 3779.2 ^{+1.8}_{-1.7} ^{+0.5}_{-0.7} ^{+0.3}_{-0.3} MeV, Γ=24.9 ^{+4.6}_{-4.0} ^{+0.5}_{-0.6} ^{+0.2}_{-0.9} 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_{ee} = 154 ^{+79}_{-58} ^{+17}_{-9} ^{+13}_{-25} eV, (2) Γ_{ee} = 414 ^{+72}_{-80} ^{+24}_{-26} ^{+90}_{-10} eV. Our statistics are insufficient to prefer one solution to another. The solution (2) mitigates the problem of non-$D\bar{D}$ 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 can not be directly compared with the corresponding PDG values obtained ignoring this effect.

hep-ex↗
arXiv2011

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 $θ= 55 ÷75^{\circ}$ and $θ= 15 ÷25^{\circ}$) and 1 GeV ($θ= 65 ÷105^{\circ}$). We briefly describe the experimental method, paying special attention to the radiative corrections. Some preliminary results are presented.

nucl-ex↗
arXiv2011

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

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 value M = 3686.114 +- 0.007 +- 0.011 ^{+0.002}_{-0.012} MeV and the product of the electron partial width by the branching fraction into hadrons Γ_{ee}*B_{h} = 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 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): Γ_{ee} =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.

hep-ex↗
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↗
arXiv2008

The beam energy calibration system for the BEPC-II collider

This document contains a proposal of the BEPC-II collider beam energy calibration system (IHEP, Beijing). The system is based on Compton backscattering of carbon dioxide laser radiation, producing a beam of high energy photons. Their energy spectrum is then accurately measured by HPGe detector. The high-energy spectrum edge will allow to determine the average electron or positron beam energy with relative accuracy about 3x10^-5.

physics.acc-ph↗
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↗