Classification of the scalar mesons: a strange pole expedition into charm and beauty territory

Abstract

The classification of scalar and vector mesons is reviewed within the framework of the Resonance-Spectrum Expansion (RSE). This method allows a simple and straightforward description of non-exotic meson-meson scattering, incorporating the effects of quark confinement and OZI-allowed decay in a fully nonperturbative way. Results for resonances and bound states are compared to experiment, on the basis of computed pole positions and cross sections. New predictions for open-charm and -bottom scalar mesons are presented. Concretely, observed vector states for u-ubar/d-dbar, s-sbar, c-cbar, and b-bbar are reproduced, and others are predicted. In the light scalar sector, the now established two nonets, one below 1 GeV and one in the region 1.3 - 1.5 GeV, are easily described, through the appearance of extra poles in the scattering matrix. The recently found Ds0*(2317) meson is accurately reproduced by the same mechanism, as a quasi-bound state in the coupled c-sbar/DK system. In S-wave D-pion and B-pion scattering, new resonances are foreseen close to threshold, i.e., a D0* at 2.16(+-0.05) GeV some 250 MeV wide, and a B0* at 5.47(+-0.05) GeV with a width of about 50 MeV. Additional predictions concern the existence of b-sbar and b-cbar scalar mesons, stable with respect to OZI-allowed decay to BK and BD, respectively, namely at 5.61(+-0.05) GeV resp. 6.64(+-0.05) GeV.