The σ and f0(980) from Ke4⊕ππ scatterings data

We systematically reconsider, within an improved “analytic K-matrix model”, the extraction of the σ≡f0(600) and f0(980) masses, widths and hadronic couplings using new Ke4≡K→ππeνe data on ππ phase shift below 390 MeV and different sets of ππ→ππ/KK¯ scatterings data from 400 MeV to 1.4 GeV. Our results are summarized in Tables 1, 2 and 5. In units of MeV, the complex poles are: Mσ=452(12)−i260(15) and Mf=981(34)−i18(11), which are comparable with some recent high-precision determinations and with PDG values. Besides some other results, we find: |gσK+K−|/|gσπ+π−|=0.37(6) which confirms a sizeable gσK+K− coupling found earlier, and which disfavours a large ππ molecule or four-quark component of the σ, while its broad ππ width (relative to the one of the ρ-meson) cannot be explained within a q¯q scenario. The narrow ππ width of the f0(980) and the large value: |gfK+K−|/|gfπ+π−|=2.59(1.34), excludes its pure (u¯u+d¯d) content. A significant gluonium component eventually mixed with q¯q appears to be necessary for evading the previous difficulties.