On the mass, width and coupling constants of the f0(980)
  Using the pole approach we determine the mass and width of the $f_0(980)$; in particular, we analyze the possibility that two nearby poles are associated to it. We restrict our analysis to a neighborhood of the resonance, using $\pi\pi$ data for the phase shift and inelasticity, and the invariant mass spectrum of the $J/\psi\to\phi\pi\pi, \phi K\bar K$ decays. The formalism we use is based on unitarity and a generalized version of the Breit-Wigner parameterization. We find that a single pole describes the $f_0(980)$, the precise position depending upon the $\pi\pi$ data used. As a byproduct, values for the $g_{f_0\pi\pi}$ and $g_{f_0K\bar K}$ coupling constants are obtained. 
R. Escribano (UAB, IFAE), A. Gallegos, J. L. Lucio M., G. Moreno   (Guanajuato Univ.), J. Pestieau (Louvain Univ.)