Pion radiative decays of excited hidden-charm pentaquark molecules: from $\Sigma_c^{(*)}\bar{D}^{(*)}(2S)$ molecules to the reported $P_c$ states
The discovery of the hidden-charm pentaquarks \(P_c(4312)\), \(P_c(4440)\) and \(P_c(4457)\) by the LHCb Collaboration are very likely to identify as the \(\Sigma_c^{(*)}\bar{D}^{(*)}\) molecules. A natural and crucial extension is the existence of excited molecular partners built from a ground-state charmed baryon and a radially excited anti-charmed meson, namely \(\Sigma_c^{(*)}\bar{D}^{(*)}(2S)\) molecules. In a framework of chiral quark model, we systematic study pion-emission decays of such excited molecules into the known ground-state \(P_c\) molecules. Our results show that the decay widths are sensitive to the spin structures and the coupled-channel interferences, i.e., the \(\Sigma_c\bar{D}(2S)/\Sigma_c\bar{D}^*(2S)/\Sigma_c^*\bar{D}^*(2S)[1/2(1/2^-)]\) state decays to \(P_c(4440)\) with a width of several MeV, while the width to \(P_c(4457)\) is suppressed below \(0.3\) MeV due to destructive interference. The pion-emission decay can be the key to unveiling the excited molecular spectrum of hidden-charm pentaquarks and provides decisive experimental signatures. We expect the future experiments such as the LHCb and PANDA can verify our predictions.