Evidence of σ particle in J / ψ → ωππ ∗ February 3 , 2008 ( BES Collaboration )

Based on a sample of 7.8 × 10 BESI J/ψ events, the decay of J/ψ → ωππ is studied. A low mass enhancement in the ππ invariant mass spectrum recoiling against ω particle is clearly seen which does not come from the phase space effect and the background. According to PWA analysis, this low mass enhancement is a broad 0 resonance, the σ particle. If a Breit-Winger function of constant width is used to fit the σ signal, its mass and width are 384 ± 66 MeV and 458±100 MeV respectively, which correspond to the pole position at (434 ± 78 ) i (202 ± 43) MeV. PACS: 14.40.Cs, 13.25.Gv, 13.39.Mk, 13.30.Eg