On the Structure of the Scalar Mesons

We investigate the structure of the scalar mesons f0(975) and a0(980) within realistic meson-exchange models of the ππ and πη interactions. Starting from a modified version of the Jülich model for ππ scattering we perform an analysis of the pole structure of the resulting scattering amplitude and find, in contrast to existing models, a somewhat large mass for the f0(975) (mf0 = 1015 MeV, Γf0 = 30 MeV). It is shown that our model provides a description of J/ψ → φππ/φKK data comparable in quality with those of alternative models. Furthermore, the formalism developed for the ππ system is consistently extended to the πη interaction leading to a description of the a0(980) as a dynamically generated threshold effect (which is therefore neither a conventional qq state nor a KK bound state). Exploring the corresponding pole