Charmonium resonances and Fano line shapes

Anomalous line shapes of quarkonia are explained naturally as an interference effect of a $c\bar{c}$ confined closed channel with the surrounding continua, well established in other fields of physics as Fano-resonances. We discuss a quark model coupled-channel analysis describing quarkonium as a mixing of closed $Q\bar{Q}$ and molecular-like $D\bar{D}$ open channels. The asymmetric line shapes observed in $\psi (3770)$ production cross sections in $e^{+}{e}^{-}$ annihilation to $D^0{\bar{D}}^0$ and $D^{+}{D}^{-}$, respectively, are described very well. The method allows to extract directly from the data the amount of $Q\bar Q \leftrightarrow D\bar D$ configuration mixing.