Confirmation of the Sigma Meson

A very general model and an analysis of data on the lightest $0^{++}$ meson nonet shows that the $f_0\left(980\right)$ and $f_0\left(1300\right)$ resonance poles are two manifestations of the same $s\overline{s}$ state. On the other hand, the $u\overline{u}+d\overline{d}$ 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 $s=0.158-i0.235\mathrm{}{\mathrm{GeV}}^2$. This is the $\sigma$ 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 $\pi \pi$ scattering below 900 MeV and it is also the resonance required by nuclear physics.