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

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 √ 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 − → ρ 0 ρ 0 ) = 20.7 ± 0.7 ( stat ) ± 2.7 ( syst ) fb and σ ( e + e − → ϕ ρ 0 ) = 5.7 ± 0.5 ( stat ) ± 0.8 ( syst ) fb .