Constrain the $\chi_{cJ}\to D^{(*)}\bar{D}^{(*)}$ effective couplings via the $X(3872)\to \pi^0\chi_{cJ}$ decays

Abstract

The hidden-charm decays serve as irreplaceable platforms for probing the structures of charmonium-like states, such as $X(3872)$, $Y(4260)$, $Z_c(3900)$, and their heavy-quark-symmetry partners. In the hadronic molecular scenario, these hidden-charm decays are denominated by intermediate meson loops (IMLs), and the couplings of $\chi_{cJ}\to D^{(\ast)}\bar{D}^{(\ast)}$ are building blocks of the amplitudes for the pionic and radiative transitions of the charmonium-like states to the $\chi_{cJ}$ and $h_c$ states, e.g., $X(3872)\to \pi^0\chi_{cJ},\,\pi\pi\chi_{cJ},\,\gamma\chi_{cJ}$ and $Y(4260)\to \pi^0 h_c,\,\eta h_c$. These couplings can not be extracted from the partial decay widths of the $\chi_{cJ}$ directly and only have estimated values from the vector meson dominance (VMD) model. Utilizing the recent precise determination of the pole position and the isospin breaking properties of the $X(3872)$, we give an estimation on the upper bounds of the absolute values of the $\chi_{cJ}\to D^{(\ast)}\bar{D}^{(\ast)}$ couplings. Our results show that the VMD model may over estimate the $\chi_{cJ}\to D^{(\ast)}\bar{D}^{(\ast)}$ couplings considering the $X(3872)$ as a $D\bar{D}^{*}$ hadronic molecule with a binding energy about tens of keV. These upper limits can be used and tested in other hidden-charm transitions of the charmonium-like states to the $\chi_{cJ}$ and $h_c$.