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Register a new userStudy of the Process $e^+e^-to pi^+pi^-pi^+pi^-$ IN THE C.M. Energy Range 920--1060 MeV with the CMD-3 Detector
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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): $BR(phitopipipipi) = (6.5pm2.7pm1.6)times 10^{-6}$.
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The cross section of the process e+e- -> pi+pi- has been measured at the CMD-2 detector in the 370-520 MeV center-of-mass (c.m.) energy range. A systematic uncertainty of the measurement is 0.7 %. Using all CMD-2 data on the pion form factor, the pion electromagnetic radius was calculated. The cross section of muon pair production was also determined.
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.
The e+e- -> pi+pi-pi+pi- cross section has been measured using 5.8/pb of integrated luminosity collected with the CMD-2 detector at the VEPP-2M collider. Analysis of the data with a refined efficiency determination and use of both three- and four-track events allowed doubling of a data sample and reduction of systematic errors to 5-7%.
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 $omega(1420)topi^+pi^-pi^0$.
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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