Observation of ${e}^{+}{e}^{\ensuremath{-}}$ Annihilation into the $C=+1$ Hadronic Final States ${\ensuremath{\rho}}^{0}{\ensuremath{\rho}}^{0}$ and $\ensuremath{\phi}{\ensuremath{\rho}}^{0}$

Observation of $e^{+} e^{-}$ Annihilation into the $C = + 1$ Hadronic Final States $ρ^{0} ρ^{0}$ and $ϕ ρ^{0}$

B. Aubert et al. (BABAR Collaboration)

Phys. Rev. Lett. 97, 112002 – Published 14 September 2006

Abstract

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