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A very general model and an analysis of data on the lightest 0⁺⁺ meson nonet shows that the f₀(980) and f₀(1300) resonance poles are two manifestations of the same ss̄ state. On the other hand, the uū+dd̄ state, when unitarized and strongly distorted by hadronic mass shifts, becomes an extremely broad (880 MeV) and light (860 MeV) resonance, with its pole at s0ex0ex=0ex0ex0.158-i0.235GeV². This is the σ meson required by models for spontaneous breaking of chiral symmetry. It has been named the Higgs meson of QCD, because it generates most of the light hadron masses. It dominates ππ scattering below 900 MeV and it is also the resonance required by nuclear physics.
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Törnqvist et al. (1996) studied this question.
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