Fully Heavy Tetraquark Spectroscopy in the Relativistic Quark Model

Masses of the ground and excited (1P, 2S, 1D, 2P, 3S) states of the fully heavy tetraquarks, composed of charm (c) and bottom (b) quarks and antiquarks, are calculated in the diquark-antidiquark picture within the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Relativistic effects are consistently taken into account. A tetraquark is considered a bound state of a diquark and an antidiquark. The finite size of the diquark is taken into account, using the form factors of the diquark-gluon interaction. It is shown that most of the investigated states of tetraquarks lie above the decay thresholds into a meson pair; as a result, they can be observed only as broad resonances. The narrow state X(6900) recently discovered in the di-J/psi production spectrum by the LHCb, CMS and ATLAS Collaborations corresponds to an excited state of the fully charmed tetraquark. Other recently discovered exotic heavy resonances, X(6200), X(6400), X(6600), X(7200), and X(7300), can also be interpreted as the different excitations of the fully charmed tetraquark.

Automated summary

This study calculates the masses of fully heavy tetraquarks' ground and excited states (namely 1P, 2S, 1D, 2P, 3S) comprising charm and bottom quarks and antiquarks. The calculations are based on the diquark-antidiquark picture within the relativistic quark model and employ the quasipotential approach and quantum chromodynamics. The findings demonstrate that most investigated states of tetraquarks exist as broad resonances above the decay thresholds.