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

The LHCb collaboration have recently updated their analysis of the resonant J/ 𝜓 p mass spectrum in the decay $$ {\varLambda}_b^0 $$→ J/𝜓 p K−, making use of their combined Run 1 and Run 2 data. In the updated analysis, three narrow states, Pc (4312)+, Pc (4440)+, and Pc (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 JP quantum numbers of the pentaquarks. However, heavy quark symmetry restricts the observable states in Λb-baryon, as well as in the decays of the other weakly-decaying b-baryons, Ξb and Ωb. In addition, some of the pentaquark states are estimated to lie below the J/ 𝜓 p threshold in Λb-decays (and corresponding thresholds in Ξb- and Ωb-decays). They decay via c$$ \overline{c} $$ annihilation into light hadrons or a dilepton pair, and are expected to be narrower than the Pc-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.