Mass spectrum of the hidden-charm pentaquarks in the compact diquark model

A bstract The LHCb collaboration have recently updated their analysis of the resonant J/ 𝜓 p mass spectrum in the decay b⁰ Λ b 0 → J/𝜓 p K − , making use of their combined Run 1 and Run 2 data. In the updated analysis, three narrow states, P c (4312) + , P c (4440) + , and P c (4457) + , are observed. The spin-parity assignments of these states are not yet known. We interpret these narrow resonances as compact hidden-charm diquark-diquark- antiquark pentaquarks. Using an effective Hamiltonian, based on constituent quarks and diquarks, we calculate the pentaquark mass spectrum for the complete SU (3) F lowest S - and P -wave multiplets, taking into account dominant spin-spin, spin-orbit, orbital and tensor interactions. The resulting spectrum is very rich and we work out the quark flavor compositions, masses, and J P quantum numbers of the pentaquarks. However, heavy quark symmetry restricts the observable states in Λ b -baryon, as well as in the decays of the other weakly-decaying b -baryons, Ξ b and Ω b . In addition, some of the pentaquark states are estimated to lie below the J/ 𝜓 p threshold in Λ b -decays (and corresponding thresholds in Ξ b - and Ω b -decays). They decay via c c̄ c ¯ annihilation into light hadrons or a dilepton pair, and are expected to be narrower than the P c -states observed. We anticipate their discovery, as well as of the other pentaquark states present in the spectrum at the LHC, and in the long-term future at a Tera- Z factory.