arXiv subjects
Publications and source records attributed to A. A. Korol.
The process $e^+e^-\to n\bar{n}$ has been studied at the VEPP-2000 $e^+e^-$ collider with the SND detector in the energy range from threshold up to 2 GeV. As a result of the experiment, the $e^+e^-\to n\bar{n}$ cross section and effective neutron form factor have been measured.
The data acquisition (DAQ) system of the SND detector successfully operated during four data-taking seasons (2010-2013) at the e+e- collider VEPP-2000. Currently the collider is shut down for planned reconstruction, which is expected to increase the VEPP-2000 luminosity and data flow from the SND detector electronics by up to 10 times. Since current DAQ system implementation (electronics and computer part) does not have enough reserve for selection of events in the new environment without compromising quality, there arose the need for the system upgrade. Here we report on the major SND data acquisition system upgrade which includes developing new electronics for digitization and data transfer, complete redesign of the data network, increasing of the DAQ computer farm processing capacity and making the event building process concurrent. These measures will allow us to collect data flow from the most congested detector subsystems in parallel in contrast to the current situation. We would like to discuss also the possibility to implement full software trigger solution in the future.
The $e^+e^-\toηγ$ cross section has been measured in the center-of-mass energy range 1.07--2.00 GeV using the decay mode $η\to 3π^0$, $π^0\to γγ$. The analysis is based on 36 pb$^{-1}$ of integrated luminosity collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured cross section of about 35 pb at 1.5 GeV is explained by decays of the $ρ(1450)$ and $ϕ(1680)$ resonances.
The beam energy measurement system for the VEPP-2000 electron-positron collider is described. The method of Compton backscattering of $CO$ laser photons on the electron beam is used. The relative systematic uncertainty of the beam energy determination is estimated as 6\cdot10^{-5}. It was obtained through comparison of the results of the beam energy measurements using the Compton backscattering and resonance depolarization methods.
The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.
The search for lepton-flavor-violation process e^+e^-\to eμin the energy region \sqrt{s}=984 - 1060 MeV with SND detector at VEPP-2M e^+e^- collider is reported. The model independent 90% CL upper limits on the e^+e^-\to eμcross section, σ_{eμ} < 11 pb, as well as on the corresponding ϕ\to eμbranching fraction, B(ϕ\to eμ) < 2 \times 10^{-6}, for the final particles polar angles 55^\circ<θ<125^\circ, were obtained.
The cross section of the process e+e-\toμ+μ- was measured in the SND experiment at the VEPP-2M e+e- collider in the energy region \sqrt{s}=980, 1040 -- 1380 MeV. The event numbers of the process e+e-\toμ+μ- were normalized to the integrated luminosity measured using e+e-\to e+e- and e+e-\toγγprocesses. The ratio of the measured cross section to the theoretically predicted value is 1.006\pm 0.007 \pm 0.016 and 1.005 \pm 0.007 \pm 0.018 in the first and second case respectively. Using results of the measurements, the electromagnetic running coupling constant αin the energy region \sqrt{s}=1040 -- 1380 MeV was obtained <1/α> = 134.1\pm 0.5 \pm 1.2 and this is in agreement with theoretical expectation.
The $e^+e^- \to ωπ^0 \to π^0 π^0 γ$ process was investigated in the SND experiment at the VEPP-2M collider. A narrow energy interval near the $ϕ$-meson was scanned. The observed cross-section reveals, at the level of three standard deviation, the interference effect caused by $ϕ\to π^0π^0γ$ decay. The cross-section parameters, as well as the real and imaginary parts of the $ϕ$-meson related amplitude, were measured.
The cross section of the process $e^+e^- \to K^+K^-$ was measured in the energy range $\sqrt{s}$ = 1.04--1.38 GeV in the SND experiment at the VEPP-2M $e^+e^-$ collider. The measured cross section is described by the model of vector meson dominance with contributions from the light vector mesons $ρ$, $ω$, $ϕ$ and their lowest excitations. The mean statistical accuracy of the measurement is 4.4 %, and the systematic uncertainty is 5.2 %.
In the experiment with the SND detector at the VEPP-2M $e^+e^-$ collider measuring the $e^+e^-\to ηγ$ cross section in the energy range $0.6<\sqrt{s}<1.38 \mathrm{GeV}$ the reanalysis of data is performed. The goal is to improve the accuracy of the previous results by analysing ambiguities in the approximation of energy dependence of the $e^+e^-\to ηγ$ cross section, which were not taken into account in our previous study. We report new results on the approximation of the $e^+e^-\to ηγ$ cross section based on Vector Dominance Model under new model parameter assumptions.
In experiment with the SND detector at VEPP-2M $e^+e^-$ collider the $e^+e^-\toηγ$ 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 $ρ(770)$, $ω(783)$, $ϕ(1020)$, $ρ^{\prime}(1465)$ resonances and agrees with results of previous measurements. The decay probabilities $\BR(ϕ\toηγ)$, $\BR(ω\toηγ)$ and $\BR(ρ\toηγ)$ were measured with the accuracies better than or comparable to the world averages.
We present a measurement of the $e^+e^-\to K_SK_L$ cross section in the energy range $\sqrt{s}=1.04 ÷1.38$ GeV. For the energy $\sqrt{s}\geq 1.2$ GeV the cross section exceeds vector meson dominance model predictions with only $ρ(770)$, $ω(783)$, and $ϕ(1020)$ mesons taken into account. Measured cross section agrees well with previous measurements.
The corrected cross section of the e^+e^-\toπ^+π^- process measured in the SND experiment at the VEPP-2M e^+e^- collider is presented. The update is necessary due to a flaw in the e^+e^-\toπ^+π^- and e^+e^-\toμ^+μ^- Monte Carlo events generators used previously in data analysis.
The update of the e^+e^-\toπ^+π^- process cross section, measured in the energy region \sqrt{s}<1 GeV with SND detector at VEPP-2M collider is presented.
New results of the e+e- -> pi+pi-, K+K-, K_SK_L, pi0/gamma, eta0/gamma processes cross section measurements are presented. The results are based on the 30 pb^-1 data, accumulated by SND detector at VEPP-2M e+e- collider in the energy range sqrt(s)=0.4-1.4 GeV during 1995-2000 years. The comparison with existing experimental data shows that the measurement accuracy is close to or better than the world average. For the e+e- -> pi+pi- process the accuracy is about 0.01. This is important for calculation of hadronic contribution into the muon anomalous magnetic moment.
The cross section of the process e^+e^-\to π^+π^- was measured in the SND experiment at the VEPP-2M collider in the energy region 400<\sqrt[]{s}<1000 MeV. This measurement was based on about 12.4 \times 10^6 selected collinear events, which include 7.4\times 10^6 e^+e^-\to e^+e^-, 4.5\times 10^6 e^+e^-\toπ^+π^- and 0.5\times 10^6 e^+e^-\toμ^+μ^- selected events. The systematic uncertainty of the cross section determination is 1.3 %. The ρ-meson parameters were determined: m_ρ=774.9\pm 0.4\pm 0.5 MeV, Γ_ρ=146.5\pm 0.8\pm 1.5 MeV, σ(ρ\toπ^+π^-)=1220\pm 7\pm 16 nb as well as the parameters of the G-parity suppressed decay ω\toπ^+π^-: σ(ω\toπ^+π^-)=29.9\pm 1.4\pm 1.0 nb and ϕ_{ρω} = 113.5\pm 1.3\pm 1.7 degree.
The process e^+e^-\toπ^0γin the energy range \sqrt{s}=0.60-1.06 GeV was studied at VEPP-2M collider with SND detector using 14 pb^{-1} of integrated luminosity. Data were analyzed in the framework of the vector meson dominance model. Preliminary results on obtained cross-section and parameters of ρ^0, ω,ϕ\to π^0γradiative decays are presented.
The review of the SND results of the $e^+e^-\toπ^+π^-π^0$ process study in the energy range $\sqrt[]{s}=0.42$ -- 1.38 GeV at VEPP-2M collider, based on about $2\times 10^6$ selected events, is presented. The total cross section, parameters of the $ρ$, $ω$, $ϕ$ resonances, and $ω^\prime$, $ω^{\prime\prime}$ states were obtained. It was found that $ρπ$ and $ωπ^0$ intermediate states describe the reaction dynamics. The experimental data cannot be described by a sum of only $ω$, $ϕ$, $ω^\prime$ and $ω^{\prime\prime}$ resonances contributions. This can be interpreted as a manifestation of the $ρ\to 3π$ decay, suppressed by $G$-parity, with relative probability $B(ρ\to 3π) = (1.01\pm^{0.54}_{0.36}\pm 0.034) \times 10^{-4}$.