Speaker
Description
The nature of the three narrow hidden-charm pentaquark $P_c$ states, i.e., $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$, is under intense discussion since their discovery from the updated analysis of the process $\Lambda_b^0\to J/\psi p K^-$ by LHCb. We employ an coupled-channel approach to study the $P_c$ states observed by LHCb Collaborations in the molecuar picture, in which the $P_c$ states are treated as $\Sigma_c\bar{D}^{(*)}$ molecules, by including the $\Lambda_c\bar{D}^{(*)}$ and $\eta_c p$ in addition to the $J/\psi p$ as explicit inelastic channels as required by unitarity and heavy quark spin symmetry (HQSS), respectively. Since inelastic parameters are very badly constrained by the current data, different calculation schemes are considered. It is shown that to obtain cutoff independent results, OPE in the multichannel system is to be supplemented with $S$-wave-to-$D$-wave mixing contact terms. As a result, in line with our previous analysis, we demonstrate that the experimental data for the $J/\psi p$ invariant mass distribution are consistent with the interpretation of the $P_c(4312)$ and $P_c(4440)/P_c(4457)$ as $\Sigma_c\bar{D}$ and $\Sigma_c \bar{D}^{*}$ hadronic molecules, respectively, and that the data show clear evidence for a new narrow state, $P_c(4380)$, identified as a $\Sigma_c^* \bar D$ molecule, which should exist as a consequence of HQSS. However, now two solutions are found in all schemes which describe the data equally well, and thus no unambiguous conclusion about the quantum numbers of the $P_c(4440)$ and $P_c(4457)$ from data in the $J/\psi p$ channel alone is possible. It is argued though that one of these solutions, in which the quantum numbers of the $P_c(4440)$ and $P_c(4457)$ are $J^P=3/2^-$ and $1/2^-$, respectively, is theoretically preferred. Moreover, we demonstrate that the line shapes related to the $P_c(4440)$ and the $P_c(4457)$ in the $\Sigma_c^{(*)}\bar{D}$ and $\eta_c p$ mass distributions from $\Lambda_b^0\to \Sigma_c^{(*)}\bar{D} K^-$ and $\Lambda_b^0\to \eta_cp K^-$ will allow one to pin down the quantum numbers in the hadronic molecular picture, once the data are available. We also investigate possible pentaquark signals in the $\Lambda_c \bar{D}^{(*)}$ final states.
