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Recently, the LHCb Collaboration have updated their analysis of the resonant$J/\psi p$ mass spectrum in the decay $\Lambda_b^0 \to J/\psi p K^-$. In thecombined Run~1 and Run~2 LHCb data, three peaks are observed, with the former$P_c(4450)^+$ state split into two narrow states, $P_c(4440)^+$ and$P_c(4457)^+$, having the masses $M=(4440.3\pm 1.3^{+4.1}_{-4.7})$ MeV and$M=(4457.3\pm 0.6^{+4.1}_{-1.7})$ MeV, and decay widths $\Gamma=(20.6\pm4.9^{+8.7}_{-10.1})$ MeV and $\Gamma=(6.4\pm 2.0^{+5.7}_{-1.9})$ MeV,respectively. In addition, a third narrow peak, $P_c(4312)^+$, having the mass$M=(4311.9\pm 0.7^{+6.8}_{-0.6})$ MeV and decay width $\Gamma=(9.8\pm2.7^{+3.7}_{-4.5})$ MeV is also observed. The LHCb analysis is not sensitive tobroad $J/\psi p$ contributions like the former $P_c(4380)^+$, implying thatthere could be more states present in the data. Also the spin-parity, $J^P$,assignments of the states are not yet determined. We interpret these resonancesin the compact diquark model as hidden-charm diquark-diquark-antiquark baryons,having the following spin and angular momentum quantum numbers: $P_c(4312)^+=\{\bar c [cu]_{s=1} [ud]_{s=0}; L_P=0, J^P=3/2^-\}$, the $S$-wave state, andthe other two as $P$-wave states, with $P_c(4440)^+ =\{\bar c [cu]_{s=1}[ud]_{s=0}; L_P=1, J^P=3/2^+\}$ and $P_c(4457)^+ = \{\bar c [cu]_{s=1}[ud]_{s=0}; L_P=1, J^P=5/2^+ \}$. The subscripts denote the spins of thediquarks and $L_P=0,1$ is the orbital angular momentum quantum number of thepentaquark. These assignments are in accord with the heavy-quark-symmetryselection rules for $\Lambda_b$-baryon decays, in which the spin $S=0$ of thelight diquark $[ud]_{s=0}$ is conserved. The masses of observed states can beaccommodated in this framework and the two heaviest states have the positiveparities as opposed to the molecular-like interpretations.

Interpretation of the Narrow $J/\psi p$ Peaks in $\Lambda_b \to J/\psi p K^-$ Decay in the Compact Diquark Model