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Register a new userStudy of dynamics of the process $e^+e^-to pi^+pi^-pi^0$ in the energy range 1.15--2.00 GeV
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The dynamics of the process $ e^+e^- to pi^+pi^-pi^0 $ is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000 $e^+e^-$ collider. The Dalitz plot distribution and $pi^+pi^-$ mass spectrum are analyzed in a model including the intermediate states $rho(770)pi$, $rho(1450)pi$, and $omegapi^0$. As a result, the energy dependences of the $rho(770)pi$ and $rho(1450)pi$ cross sections and the relative phases between the $rho(770)pi$ amplitude and the $rho(1450)pi $ and $omegapi^0$ amplitudes are obtained. The $rho(1450)pi$ cross section has a peak in the energy region of the $omega(1650)$ resonance (1.55-1.75 GeV). In this energy range the contributions of the $rho(770)pi$ and $rho(1450)pi$ states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $rho(770)pi$ cross section. We conclude that the intermediate state $rho(1450)pi$ gives a significant contribution to the decay of $omega (1650)topi^+pi^-pi^0$, whereas the $rho(770)pi$ mechanism dominates in the decay $omega(1420)topi^+pi^-pi^0$.
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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 $B(rhoto 3pi) = (1.01pm^{0.54}_{0.36}pm 0.034) times 10^{-4}$.
In the experiment with the SND detector at VEPP-2M e^+e^- collider the process $e^+e^-topi^+pi^-pi^0$ was studied in the energy range 2E_0 from 1.04 to 1.38 GeV. A broad peak was observed with the visible mass $M_{vis}=1220pm 20$ MeV and cross section in the maximum $sigma_0simeq 4$ nb. The peak can be interpreted as a $omega$-like resonance $omega (1200)$.
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.
A cross section of the process $e^+e^- to pipipipi$ has been measured using 6798$pm$93 signal events from a data sample corresponding to an integrated luminosity of 9.8 pb$^{-1}$ collected with the CMD-3 detector in the center-of-mass energy range 920--1060 MeV. The measured cross section exhibits an interference pattern of the $phi(1020)topipipipi$ decay with a non-resonant process $e^+e^- to pipipipi$, from which we obtain the branching fraction of the doubly suppressed decays (by G-parity and OZI rule): $BR(phitopipipipi) = (6.5pm2.7pm1.6)times 10^{-6}$.
The cross section of the process $e^+e^- to 3(pi^+pi^-)$ has been measured using 22 pb$^{-1}$ of integrated luminosity collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider in the c.m. energy range 1.5 -- 2.0 GeV. The measured cross section exhibits a sharp drop near the $pbar p$ threshold. A first study of dynamics of six-pion production has been performed.
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