The LHCb Collaboration announced the observation of three narrow structures consistent with hidden-charm pentaquark states. They are candidates of hadronic molecules formed of a pair of a charmed baryon and an anticharmed meson. Among them, the P c (4457) mass is consistent with earlier predictions of a Σ cD * molecule with I = 1/2. We point out that if such a picture were true, one would have B(P c (4457) → J/ψ∆ + )/B(P c (4457) → J/ψp) at the level ranging from a few percent to about 30%. Such a large isospin breaking decay ratio is two to three orders of magnitude larger than that for normal hadron resonances. It is a unique feature of the Σ cD * molecular model, and can be checked by LHCb. * Four years after the discovery of the hidden-charm pentaquark-like states P c (4380) and P c (4450) [1], with the full set of Run-1 and Run-2 data the LHCb Collaboration announced the observation of more structures consistent with hidden-charm pentaquark states with masses and widths given by [2, 3] M Pc(4312) + = 4311.9 ± 0.7 +6.8 −0.6 MeV, Γ Pc(4312) + = 9.8 ± 2.7 +3.7 −4.5 MeV, M Pc(4440) + = 4440.3 ± 1.3 +4.1 −4.7 MeV, Γ Pc(4440) + = 20.6 ± 4.9 +8.7 −10.1 MeV,
We investigate the consequences of heavy quark spin symmetry (HQSS) on hidden-charm pentaquark P c states. As has been proposed before, assuming the P c (4440) and the P c (4457) as S-wavē D * Σ c molecules, seven hadronic molecular states composed ofDΣ c ,DΣ * c ,D * Σ c , andD * Σ * c can be obtained, with theDΣ c molecule corresponding to the P c (4312). These seven states can decay into J/ψN and η c N , and we use HQSS to predict ratios of partial widths of the S-wave decays.For the decays into J/ψN , it is found that among all six P c molecules with spin 1/2 or 3/2, at least four states decay much more easily into the J/ψN than the P c (4312), and two of them couple dominantly to theD * Σ * c . While no significant peak around theD * Σ * c threshold is found in the J/ψp distribution, these higher P c states either are produced with lower rates or some special production mechanism for the observed P c states might play an important role, such as an intricate interplay between the production of pentaquarks and triangle singularities.
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