Interpretation of LHCb hidden-charm pentaquarks within the compact diquark model

Abstract

The LHCb collaboration have recently updated their analysis of the resonant J/? p mass spectrum in the decay ?0b ? J/? 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 ?b-baryon, as well as in the decays of the other weakly-decaying b-baryons, ?b and Ob. In addition, some of the pentaquark states are estimated to lie below the J/? p threshold in ?b-decays (and corresponding thresholds in ?b- and Obdecays). They decay via cc¯ 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.