Unified coupled-channel description for the five near-threshold structures $\psi(3770)$, $G(3900)$, $R(3760)$, $R(3780)$ and $R(3810)$ from $e^+e^-$ annihilation

Abstract

The recent observation of multiple near-threshold structures in $e^+e^-$ annihilation-including $\psi(3770)$, $G(3900)$, $R(3760)$, $R(3780)$, and $R(3810)$-reveals limitations in existing models of charmonium and exotic hadrons. In this paper, we propose a unified coupled-channel description that simultaneously incorporates all five near-threshold structures using parameters constrained by hadron spectroscopy. Our model accurately reproduces the line shapes in both $D\bar{D}$ and nonopen-charm hadron (nOCH) channels, resolves the asymmetric profile of $\psi(3770)$, and produces the $G(3900)$ bump. We identify the $R(3780)$ as the dominant manifestation of $\psi(3770)$, attribute $R(3760)$ to $D\bar{D} \to \text{nOCH}$ rescattering and suggest that $R(3810)$ arises from coupling between the $\psi(1D)$ state and the $h_c\pi\pi$ channel. The significant non-$D\bar{D}$ decay of $\psi(3770)$ is explained by its near-threshold position. This analysis provides a coherent, unquenched framework centered on a charmonium $\psi(1D)$ core for near-threshold phenomena and offers a predictive approach extendable to bottomonium systems and future data from Belle II.