In production processes, e.g. J/Ψ → ωππ or p̄p → 3π, the σ and f0(980) overlap in the same partial wave. The conjecture of Extended Unitarity (EU) states that the ππ pair should have the same phase variation as ππ elastic scattering. This is an extension of Watson’s theorem beyond its original derivation, which stated only that the s-dependence of a single resonance should be universal. The pred...
