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Register a new userStudy of the process $e^+e^- to pi^+pi^-$ in the energy region 400<sqrt[]{s}<1000 MeV
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The cross section of the process e^+e^-to pi^+pi^- 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 7.4times 10^6 e^+e^-to e^+e^-, 4.5times 10^6 e^+e^-topi^+pi^- and 0.5times 10^6 e^+e^-tomu^+mu^- selected events. The systematic uncertainty of the cross section determination is 1.3 %. The rho-meson parameters were determined: m_rho=774.9pm 0.4pm 0.5 MeV, Gamma_rho=146.5pm 0.8pm 1.5 MeV, sigma(rhotopi^+pi^-)=1220pm 7pm 16 nb as well as the parameters of the G-parity suppressed decay omegatopi^+pi^-: sigma(omegatopi^+pi^-)=29.9pm 1.4pm 1.0 nb and phi_{rhoomega} = 113.5pm 1.3pm 1.7 degree.
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The cross section of the process $e^+e^-to pi^+pi^-pi^0$ was measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the energy region $sqrt[]{s}$ below 980 MeV. This measurement was based on about $1.2 times 10^6$ selected events. The obtained cross section was analyzed together with the SND and DM2 data in the energy region $sqrt[]{s}$ up to 2 GeV. The $omega$-meson parameters: $m_omega=782.79pm 0.08pm 0.09$ MeV, $Gamma_omega=8.68pm 0.04pm 0.15$ MeV and $sigma(omegato 3pi)=1615pm 9pm 57$ nb were obtained. It was found that the experimental data cannot be described by a sum of only $omega$, $phi$, $omega^prime$ and $omega^{primeprime}$ resonances contributions. This can be interpreted as a manifestation of $rhoto 3pi$ decay, suppressed by $G$-parity, with relative probability $B(rhoto 3pi) = (1.01pm^{0.54}_{0.36}pm 0.034) times 10^{-4}$.
The corrected cross section of the e^+e^-topi^+pi^- 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^-topi^+pi^- and e^+e^-tomu^+mu^- Monte Carlo events generators used previously in data analysis.
The cross section of the process $e^+e^-to pi^+pi^-pi^0$ was measured in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region $sqrt[]{s} = 980 div 1380$ MeV. The measured cross section, together with the $e^+e^-to pi^+pi^-pi^0$ and $omegapi^+pi^-$ cross sections obtained in other experiments, was analyzed in the framework of the generalized vector meson dominance model. It was found that the experimental data can be described by a sum of $omega$, $phi$ mesons and two $omega^prime$ and $omega^{primeprime}$ resonances contributions, with masses $m_{omega^prime}sim 1490$,$m_{omega^{primeprime}}sim 1790$ MeV and widths $Gamma_{omega^prime}sim 1210$, $Gamma_{omega^{primeprime}}sim 560$ MeV. The analysis of the $pi^+pi^-$ invariant mass spectra in the energy region $sqrt[]{s}$ from 1100 to 1380 MeV has shown that for their descriptionone should take into account the $e^+e^-toomegapi^0topi^+pi^-pi^0$ mechanism also. The phase between the amplitudes corresponding to the $e^+e^-toomegapi$ and $e^+e^-torhopi$ intermediate states was measured for the first time. The value of the phase is close to zero and depends on energy.
The invariant mass spectra of the $pi^+pi^-$ and $pi^pmpi^0$ pairs in the process $e^+e^- to pi^+pi^-pi^0$ were studied in the SND experiment at the VEPP-2M collider in the energy region $sqrt[]{s} simeq 1020$ MeV. These studies were based on about $0.5 times 10^6$ experimental events. The spectra were analyzed in the framework of the vector meson dominance model. It was found that the experimental data can be described with $e^+e^- to rhopi to pi^+pi^-pi^0$ transition only. Upper limit on the branching ratio of the $phi(1020)topi^+pi^-pi^0$ decay through intermediate states different from $rhopi$ was obtained at the 90 % confidence level: $B(phitopi^+pi^-pi^0)<6 cdot 10^{-4}$. The $rho$-meson mass and width which follow from the spectra analysis are $m_rho=775.0pm 1.3$ MeV, $Gamma_rho=150.4 pm 3.0$ MeV. Neutral and charged $rho$-mesons mass difference was found to equal $m_{rho^pm}-m_{rho^0}=-1.3pm2.3$ MeV. In the $pi^+pi^-$ mass spectrum the $rho-omega$ interference was seen at two standard deviations level.
The cross section of the process e+e-tomu+mu- 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-tomu+mu- were normalized to the integrated luminosity measured using e+e-to e+e- and e+e-togammagamma processes. The ratio of the measured cross section to the theoretically predicted value is 1.006pm 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 alpha in the energy region sqrt{s}=1040 -- 1380 MeV was obtained <1/alpha> = 134.1pm 0.5 pm 1.2 and this is in agreement with theoretical expectation.
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