اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدStudy of the process $e^+e^- to pi^+pi^-pi^0$ in the energy region $sqrt[]{s}$ below 0.98 GeV
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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 $B(rhoto 3pi) = (1.01pm^{0.54}_{0.36}pm 0.034) times 10^{-4}$.
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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 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.
The process $e^+e^- to pi^+pi^-pi^0eta$ is studied in the center-of-mass energy region below 2 GeV with the SND detector at the VEPP-2000 $e^+e^-$ collider. The four intermediate states contribute to this process: $omegaeta$, $phieta$, $a_0(980)rho$,
and a structureless $pi^+pi^-pi^0eta$ state. We measure the total $e^+e^- to pi^+pi^-pi^0eta$ cross section and the cross sections for its components: $omegaeta$, $phieta$, and a sum of $a_0(980)rho$ and the structureless state. Our results are in agreement with previous measurements and have comparable or better accuracies.
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 ar
e 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 $omega(1420)topi^+pi^-pi^0$.
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.
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