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Register a new userEnergy calibration of the NaI(Tl) calorimeter of the SND detector using $e^+e^- to e^+e^-$ events
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Calibration of the three layer NaI(Tl) spherical calorimeter of the SND detector using electron -- positron scattering events is described. Energy resolution of $5 % (FWHM/2.36)$ for 500 MeV photons was achieved.
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The technique of discrimination of the $e^+e^-to e^+e^-$ and $e^+e^-to pi^+pi^-$ events in energy range $0.5 < sqrt{s} < 1$ GeV by energy deposition in the calorimeter of SND detector was developed by applying machine learning method. Identification efficiency for $e^+e^-to e^+e^-$ and $e^+e^-to pi^+pi^-$ events in the range from 99.3 to 99.8 % has been achived.
Results of the SND experiment at the VEPP-2M e+ e- collider on the QED processes e+ e- --> e+ e- gamma and e+ e- --> e+ e- gamma gamma with production at large angles are presented. Energy and angular distributions of the final particles were studied. No deviations from QED with an accuracy of 3.8% for the first process and 10.3% for the second were found.
In experiment with the SND detector at VEPP-2M $e^+e^-$ collider the $e^+e^-toetagamma$ cross section was measured in the energy range $E$=0.60--1.38 GeV with the integrated luminosity of 27.8 pb$^{-1}$. The measured cross section is well described by the vector meson dominance model with contributions from the $rho(770)$, $omega(783)$, $phi(1020)$, $rho^{prime}(1465)$ resonances and agrees with results of previous measurements. The decay probabilities $BR(phitoetagamma)$, $BR(omegatoetagamma)$ and $BR(rhotoetagamma)$ were measured with the accuracies better than or comparable to the world averages.
A search for the process $e^+e^- to eta^prime$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The data were accumulated at the center-of-mass energy of $957.78pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $eta^prime$ meson five decay chains have been used: $eta^{prime}toetapi^+pi^-$ followed by the $eta$ decays to $gammagamma$ and $3pi^0 $, and $eta^{prime} to etapi^0pi^0$ followed by the $eta$ decays to $pi^+pi^-pi^0$, $gammagamma$, and $3pi^0$. As a result, the upper limit has been set on the $eta^prime$ electronic width: $Gamma_{eta^{prime}to e^+e^-} < 0.0020$ eV at the 90% confidence level.
The process $e^+e^-to K^+K^-pi^0$ is studied with the SND detector at the VEPP-2000 $e^+e^-$ collider. Basing on data with an integrated luminosity of 26.4~pb$^{-1}$ we measure the $e^+e^-to K^+K^-pi^0$ cross section in the center-of-mass energy range from 1.28 up to 2 GeV. The measured mass spectrum of the $Kpi$ system indicates that the dominant mechanism of this reaction is the transition through the $K^{ast}(892)K$ intermediate state. The cross section for the $phipi^0$ intermediate state is measured separately. The SND results are consistent with previous measurements in the BABAR experiment and have comparable accuracy. We study the effect of the interference between the $phipi^0$ and $K^ast K$ amplitudes. It is found that the interference gives sizable contribution to the measured $e^+e^- to phi pi^0to K^+K^-pi^0$ cross section below 1.7 GeV.
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