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

Three hidden-charm pentaquark P-c states, P-c(4312), P-c(4440), and P-c(4457) were revealed in the A(b)(0) -> J/psi pK(-) 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/psi p 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 Sigma((*))(c) (D) over bar ((*)) molecular states in two spin multiplets, such that the P-c(4312) is mainly a Sigma(c)(D) over bar bound state with J(P) = 1/2(-), while P-c(4440) and P-c(4457) are Sigma(c)(D) over bar* hound states with quantum numbers 3/2(-) and 1/2(-), respectively. We also show that there is evidence for a narrow Sigma(c)*(D) over bar hound state in the data which we call P-c(4380), different from the broad one reported by LHCb in 2015. With this state included, all predicted Sigma(c)(D) over bar, Sigma(c)*(D) over bar, and Sigma(c)(D) over bar* hadronic molecules are seen in the data, while the missing three Sigma(c)*(D) over bar* states are expected to be found in future runs of the LHC or in photoproduction experiments.