The form of resonance line-shapes unveils information about its nonperturbative properties and formation mechanisms. Here, we study the non-Breit-Wigner energy distribution of the resonance $\psi (3770)$ using an unitarized effective Lagrangian approach, that includes the effect of the nearby threshold $D^{ +}D^{ -}$. Two poles are found in the second Riemann sheet near the resonance amplitude. We discuss the setting of the free parameters and possible effects contributing to the signal.
Categories: hep-ph