On the kappa, page 2    1 3 4

   In 1986 we published a paper on the issue, in which we also showed that the same technique applies to S-wave pion-eta and pion-kaon scattering data.
   For each case we could associate the appearance of a large signal in the scattering cross section with a pole structure of the analytic continuation of the scattering amplitude in the complex-invariant-mass plane.
   Actually, we produced an infinity of such poles, each related to one of the states in the bare quark-antiquark spectrum.
   But, there appeared, furthermore, several "unexpected" poles, which are nowadays called "dynamically generated poles". In pion-kaon S-wave scattering we found one such pole below 1.0 GeV, which describes the large signal at around 0.83 GeV (see picture at page 1), called "kappa", or, K0*(800). In pion-eta S-wave scattering we also found one such pole below 1.0 GeV, the "delta", or, a0(980). However, in pion-pion S-wave scattering there are two such poles below 1.0 GeV, the "sigma", or, f0(600), and the "S*", or, f0(980).
   In all, we found nine "unexpected" poles below the invariant mass of 1.0 GeV, four kappas (a neutral kappa and its neutral anti-particle, a positively charged kappa and a negatively charged kappa), three deltas (one neutral and two charged) , one sigma and one S*. Nine, since nine is just the number of different combinations of one quark and one anti-quark you can make with three quarks, up, down and strange, and three anti-quarks, anti-up, anti-down and anti-strange. They form the nonet of scalar mesons, which are still today disputed.


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