Relativistic Description of Fully Heavy Tetraquark Spectroscopy

Spectroscopy of the fully heavy tetraquarks with open charm and/or bottom is studied within the relativistic quark model, based on the quasipotential approach and QCD. A special emphasize is given to the asymmetric in flavor compositions. A tetraquark is considered as a bound state of a diquark and an antidiquark which are treated as a spatially extended colored objects and interact as a whole. Relativistic effects are consistently taken into account. It is found, that a significant mixing between the asymmetric in flavor states of tetraquarks occurs for the same total momentum-parity ( $$J^{P}$$ ), but different full spins of the tetraquark ( $$S$$ ) within the same excitation. We confront the calculated masses of such tetraquarks with the fall-apart decay thresholds into a pair of heavy mesons. Such comparison allows us to select states that could be observed as narrow resonances.