HU-SEFT R 1996-18 THE SCALAR qq̄ NONET AND CONFIRMATION OF THE BROAD σ(≈ 500) MESON

The available data on the a0(980), f0(980), f0(1300) and K 0 (1430) mesons are fitted as a distorted 0 qq̄ nonet using only 6 parameters and a very general model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. One finds that with the large overall coupling there can appear two physical resonance poles from only one qq̄ state. Thus 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 Breit-Wigner-like background, mBW = 860 MeV, ΓBW = 880 MeV, with its pole at s=(0.158-i0.235) GeV. This is the σ meson required by models for spontaneous breaking of chiral symmetry.