Two-resonance structure of the (I JPC = 0 0++) ππ-amplitude in a mass region around 1 GeV

The structure of the (I = 0, JPC = 0++) S-wave ππ-amplitude up to an invariant energy of 1.15 GeV is determined from a simultaneous analysis of the GAMS data on the π−p → π0π0n reaction in a set of 4-momentum transfer squared intervals, together with the S-wave ππ phase shift (CERN-Munich data) and the Crystal Barrel data on the pp → π0π0π0, pp → ηηπ0 and pp → ηπ0π0 annihilations at rest. The analysis shows the existence of two resonances near the KK threshold: a narrow one with a mass of 987 MeV and a width of 80 MeV, and a wide one with a mass of 1160 MeV and a width about 900 MeV. These physical states appear as a result of mixing of two original states with masses ≈ 800 MeV and ≈ 1200 MeV. The first one is a candidate for the σ-resonance.