Study of theππmass spectra in the processe+e−→π+π−π0ats≃1020MeV

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Abstract

The invariant mass spectra of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{0}$ pairs in the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ were studied in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region $\sqrt{s}\ensuremath{\simeq}1020$ MeV. These studies were based on about $0.5\ifmmode\times\else\texttimes\fi{}{10}^{6}$ events. The spectra were analyzed in the framework of the vector meson dominance model. It was found that the experimental data can be described assuming the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\rho}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\pi}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ transition only. An upper limit on the branching ratio of the $\ensuremath{\varphi}(1020)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay through intermediate states different from $\ensuremath{\rho}\ensuremath{\pi}$ was obtained at the $90%$ confidence level: $B(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\varphi}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})<6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ The \ensuremath{\rho}-meson mass and width which follow from the spectra analysis are ${m}_{\ensuremath{\rho}}=775.0\ifmmode\pm\else\textpm\fi{}1.3$ MeV, ${\ensuremath{\Gamma}}_{\ensuremath{\rho}}=150.4\ifmmode\pm\else\textpm\fi{}3.0$ MeV. The mass difference of the neutral and charged $\ensuremath{\rho}$ mesons was found to equal ${m}_{{\ensuremath{\rho}}^{\ifmmode\pm\else\textpm\fi{}}}\ensuremath{-}{m}_{{\ensuremath{\rho}}^{0}}=\ensuremath{-}1.3\ifmmode\pm\else\textpm\fi{}2.3$ MeV. In the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ mass spectrum the $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ interference was seen at a two standard deviation level.

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