Interpretation of the LHCb Pc States as Hadronic Molecules and Hints of a Narrow Pc(4380)

Three hidden-charm pentaquark Pc states, Pc(4312), Pc(4440), and Pc(4457) were revealed in the Λb0→J/ψpK− process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the J/ψp invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven Σc(*)D¯(*) molecular states in two spin multiplets, such that the Pc(4312) is mainly a ΣcD¯ bound state with JP=1/2−, while Pc(4440) and Pc(4457) are ΣcD¯* bound states with quantum numbers 3/2− and 1/2−, respectively. We also show that there is evidence for a narrow Σc*D¯ bound state in the data which we call Pc(4380), different from the broad one reported by LHCb in 2015. With this state included, all predicted ΣcD¯, Σc*D¯, and ΣcD¯* hadronic molecules are seen in the data, while the missing three Σc*D¯* states are expected to be found in future runs of the LHC or in photoproduction experiments.