Production of $P_c $ states from $\Lambda_b$ decay

In the present work, we investigate $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ production from $\Lambda_b$ decay in a molecular scenario by using an effective Lagrangian approach. We predict the ratio of the branching fraction of $\Lambda_b \to P_c K$, which is weakly dependent on our model parameter. We also find the ratios of the productions of the branching fractions of $\Lambda_b \to P_c K$ and $P_c \to J/\psi p$ can be well interpreted in the molecular scenario. Moreover, the estimated branching fractions of $\Lambda_b \to P_c K$ are of order $10^{-6}$, which could be tested by further measurements in LHCb Collaboration.