Analysis on the composite nature of the light scalar mesons f0(980) and a0(980)

We study the weight or compositeness of the x-x- ??? KK?? and x-ri ??? KK?? in the composition of the f0(980) and a0(980) resonances, respectively. Either we use the saturation of the total width and compositeness, or we use a Flatte??parametrization taking also into account the spectral function of a near-threshold resonance. We make connections and compare between these two methods. We take input values for the pole mass and width and, in addition, for the total compositeness or the decay-width branching ratio to the lighter channel for each resonance. It turns out that for the poles considered the meson-meson components are dominant for the f0(980), while for the a0(980) resonance they are subdominant. We also provide partial decay widths and partial compositeness coefficients, so that the KK?? component is the most important one for the f0(980). Additionally, this study stresses the need to distinguish between the bare and dressed couplings and widths in a Flatte?? parametrization. We elaborate on the connection between the partial-decay widths calculated in terms of the dressed couplings and the actual measured ones. Due to the coupled-channel dynamics when the pole lies near the heavier threshold in the second Riemann sheet some changes are needed with respect to standard relations.

Automated summary

This study investigates the composition and importance of the x-x- ??? KK?? and x-ri ??? KK?? components in the f0(980) and a0(980) resonances. It is found that the meson-meson components dominate in the f0(980) while they are subdominant in the a0(980) resonance. The study also emphasizes the need to distinguish between bare and dressed couplings and widths in the parameterization.