Line-shape analysis of charmonium resonances

We discuss weather the new enhancements found by BES, alias the $Y(4220)$, $Y(4260)$, $Y(4360)$, and $Y(4390)$ are true resonances. We argue that the nearby thresholds $D_s^{\ast }{\bar{D}}_s^{\ast }$, $D{\bar{D}}_1+\bar{D}{D}_1$, $D_s{\bar{D}}_{s1}+\overline{D_s}{D}_{s1}$ and $D^{\ast }{\bar{D}}_1+{\bar{D}}^{\ast }{D}_1$, as well as the $\psi (4160)$ and $\psi (4415)$ states have a strong influence over the observed $J\mathrm{/}\psi {\pi }^{+}{\pi }^{-}$ and $h_c{\pi }^{+}{\pi }^{-}$ line-shapes. We propose an unitarized effective Lagrangian model to study the dynamical effect of the interaction between each known $\psi$ state and its closest thresholds. In addition, we present some of our recent motivating results, using the same model, for the $\psi (3770)$ resonance, where the distortion from a Breit-Wigner line-shape is shown to result not only from the kinematic interference, but also from the influence of the $D^0{\bar{D}}^0+D^{+}{D}^{-}$ one-loops. Moreover, two poles were found, at about 3.78 GeV and at 3.74 GeV, the second one generated dynamically, yet contributing to the distortion of the line-shape.