A discussion on the anomalous threshold enhancement of $J/\psi$ -- $\psi (3770)$ couplings and $X(6900)$ peak

Ye Lu, Chang Chen, Guang-you Qin +1

The attractive interaction between $J/\psi$ and $\psi (3770)$ has to be strong enough to form the molecular resonant structure, i.e., $X(6900)$. We argue that since $\psi (3770)$ decays predo…