Three hidden-charm pentaquark Pc states, Pc(4312), Pc(4440) and Pc(4457) were revealed in the Λ 0 b → 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 coupledchannel formalism taking into account heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven Σ ( * ) cD ( * ) molecular states in two spin multiplets, such that the Pc(4312) is mainly a ΣcD bound state with J P = 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 clear evidence for a narrow Σ * cD bound state in the data which we call Pc(4380), different from the broad one reported by LHCb in 2015. With this state established, all predicted ΣcD, Σ * cD , and ΣcD * hadronic molecules are seen in the data, while the missing three Σ * cD * states with smaller production rates are expected to be found in future runs of the LHC or in photoproduction experiments.

We have used QCD sum rules to study the newly observed charged state Z c (4025) as a hidden-charm D * D * molecular state with the quantum numbers I G (J P ) = 1 + (1 + ). Using a D * D * molecular interpolating current, we have calculated the two-point correlation function and the spectral density up to dimension eight at leading order in α s . The extracted mass is m X = (4.04 ± 0.24) GeV. This result is compatible with the observed mass of Z c (4025) within the errors, which implies a possible molecule interpretation of this new resonance. We also predict the mass of the corresponding hidden-bottom B * B * molecular state: m Z b = (9.98 ± 0.21) GeV.

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Since 2003 many new hadrons, including the lowest-lying positive-parity charm-strange mesons D * s0 (2317) and Ds1 (2460), were observed that do not conform with quark model expectations. It was recently demonstrated that various puzzles in the charm meson spectrum find a natural resolution, if the SU(3) multiplets for the lightest scalar and axial-vector states, amongst them the D * s0 (2317) and the Ds1 (2460), owe their existence to the nonperturbative dynamics of Goldstone-Boson scattering off D (s) and D * (s) mesons. Most importantly the ordering of the lightest strange and nonstrange scalars becomes natural. In this work we demonstrate for the first time that this mechanism is strongly supported by the recent high quality data on the B − → D + π − π − provided by the LHCb experiment. This implies that the lowest quark-model positive-parity charm mesons, together with their bottom counterparts, if realized in nature, do not form the ground-state multiplet. This is similar to the pattern that has been established for the scalar mesons made from light up, down and strange quarks, where the lowest multiplet is considered to be made of states not described by the quark model. In a broader view, the hadron spectrum must be viewed as more than a collection of quark model states.One of the currently most challenging problems in fundamental physics is to understand the nonperturbative regime of the Quantum Chromodynamics (QCD), the fundamental theory for the interaction of quarks and gluons. However, since the quark and gluon fields are confined inside color-neutral hadrons, what needs to be achieved is a quantitative understanding of the hadron spectrum. First principle lattice QCD (LQCD) calculations are indispensable in this regard. In many cases, one can efficiently bridge the computationally intensive LQCD framework with complicated experimental observables using chiral perturbation theory (ChPT)-the effective field theory for QCD at low energies-and its unitarization to fulfill probability conservation. In this work we demonstrate how such a combination leads to the resolution of a number of longstanding puzzles in charmmeson spectroscopy. It also paves the way towards a new paradigm in the spectroscopy for heavy-light mesons.Until the beginning of the millennium heavy-hadron spectroscopy was assumed to be well understood by means of the quark model [1,2], which describes the positive-parity ground state charm mesons as bound systems of a heavy quark and a light antiquark in a Pwave. This belief was put into question in 2003, when the charm-strange scalar (J P = 0 + ) and axial-vector (1 + ) mesons D * s0 (2317) [3] and D s1 (2460) [4] were discov- * fkguo@itp.ac.cn ered (for recent reviews on new hadrons, see Refs.[5-11]), since the states showed properties at odds with the quark model. Moreover, attempts to adjust the quark model raised more questions [12]. Various alternative proposals were put forward about the nature of these new states including D ( * ) K hadronic molecules (loosely bound states of two ...

We derive the scattering amplitude for Goldstone bosons of chiral symmetry off the pseudoscalar charmed mesons up to leading one-loop order in a covariant chiral effective field theory, using the so-called extended-on-mass-shell renormalization scheme. Then we use unitarized chiral perturbation theory to fit to the available lattice data of the S-wave scattering lengths. The lattice data are well described. However, most of the low-energy constants determined from the fit bear large uncertainties. Lattice simulations in more channels are necessary to pin down these values which can then be used to make predictions in other processes related by chiral and heavy quark symmetries.