Pentaquarks with hidden charm as hadroquarkonia

We consider hidden charm pentaquarks as hadroquarkonium states in a QCD inspired approach. Pentaquarks arise naturally as bound states of quarkonia excitations and ordinary baryons. The LHCb P_c(4450) pentaquark is interpreted as a ψ^′-nucleon bound state with spin-parity J^P= 3 / 2 ^-. The partial decay width Γ(P_c(4450) → J/ ψ+ N) ≈ 11 MeV is calculated and turned out to be in agreement with the experimental data for P_c(4450). The P_c(4450) pentaquark is predicted to be a member of one of the two almost degenerate hidden-charm baryon octets with spin-parities J^P= 1 / 2 ^-, 3 / 2 ^-. The masses and decay widths of the octet pentaquarks are calculated. The widths are small and comparable with the width of the P_c(4450) pentaquark, and the masses of the octet pentaquarks satisfy the Gell-Mann–Okubo relation. Interpretation of pentaquarks as loosely bound Σ_cD¯ ^∗ and Σc∗D¯∗ deuteronlike states is also considered. We determine quantum numbers of these bound states and calculate their masses in the one-pion exchange scenario. The hadroquarkonium and molecular approaches to exotic hadrons are compared and the relative advantages and drawbacks of each approach are discussed.