We assume that the two hidden charm pentaquark states discovered at $LHCb$ are built from three light quarks and a $c\overline{c}$ pair. Further assumed is that the three light quarks and the $c\overline{c}$ pair are both in colour octet states. Thus, for the final $J^P={\frac{5}{2}}^{+}$ state, the three light quarks and the $c\overline{c}$ pair are in a relative P-state, whereas the five constituents are in a relative S-state forming the four $J^P={\frac{3}{2}}^{-}$ states, the four eigenstates of the chromomagnetic Hamiltonian with masses 4360, 4409, 4491 and 4560 MeV. The “open channel” [$p+J/\psi$] has large components along the two lower mass states and they thus appear as a resonance with a mass 4380 MeV, whereas [${\mathrm{\Lambda }}_c{\overline{D}}^{*}$] and [${\mathrm{\Sigma }}_c{\overline{D}}^{*}$] are “open channels” respectively for the two lowest and the two highest mass resonances, respectively. The small width of the $5/2^{+}$ state is due to the fact that its decay requires one-gluon exchange. The decays of particles with beauty furnish the best experimental technique for discovering multiquark states with hidden charm. Also, the mechanism of production proposed here explains why only a few states with nonminimal constituents have been discovered so far.

• Received 21 June 2018

DOI:https://doi.org/10.1103/PhysRevD.98.114011

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Published by the American Physical Society