v 1 2 3 D ec 2 00 0 103 Light σ - Meson Production in Excited Υ Decay Processes I — Analyses —

We analyze the ππ production amplitudes in the excited Υ decay processes, Υ (2S) → Υ (1S)ππ, Υ (3S) → Υ (1S)ππ and Υ (3S) → Υ (2S)ππ, and the ππ and KK̄ production amplitudes in the charmonium decay processes, ψ(2S) → J/ψππ and J/ψ → φππ, φKK. The amplitudes are parametrized by the sum of Breit-Wigner amplitudes for the σ and the other relevant particles and of the direct 2π-production amplitude, following the VMW method. All the ππ (and KK̄) invariant mass spectra are reproduced well with the σ Breit-Wigner amplitude by using the common parameters, mσ = 526 +48 −37MeV and Γσ = 301 +145 −100MeV, which is almost consistent with the values obtained in our previous phase shift analyses. This strongly suggests the existence of light σ-meson.