Observation of e+e− Annihilation into the C=+1 Hadronic Final States ρ0ρ0 and ϕρ0

Le résumé fourni par la source

We report the first observation of ${e}^{+}{e}^{\ensuremath{-}}$ annihilation into states of positive $C$ parity, namely, ${\ensuremath{\rho}}^{0}{\ensuremath{\rho}}^{0}$ and $\ensuremath{\phi}{\ensuremath{\rho}}^{0}$. The two states are observed in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${K}^{+}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ final states, respectively, in a data sample of $225\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the BABAR experiment at the Positron-Electron Project II ${e}^{+}{e}^{\ensuremath{-}}$ storage rings at energies near $\sqrt{s}=10.58\text{ }\text{ }\mathrm{GeV}$. The distributions of $\mathrm{cos}{\ensuremath{\theta}}^{*}$, where ${\ensuremath{\theta}}^{*}$ is the center-of-mass polar angle of the $\ensuremath{\phi}$ meson or the forward ${\ensuremath{\rho}}^{0}$ meson, suggest production by two-virtual-photon annihilation. We measure cross sections within the range $|\mathrm{cos}{\ensuremath{\theta}}^{*}|<0.8$ of $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}{\ensuremath{\rho}}^{0})=20.7\ifmmode\pm\else\textpm\fi{}0.7(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}2.7(\mathrm{syst})\text{ }\text{ }\mathrm{fb}$ and $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\rho}}^{0})=5.7\ifmmode\pm\else\textpm\fi{}0.5(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.8(\mathrm{syst})\text{ }\text{ }\mathrm{fb}$.

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