Towards the understanding of fully-heavy tetraquark states from various models

We use a color-magnetic interaction model (CMIM), a traditional constituent quark model and a multiquark color flux-tube model to systematically investigate the properties of the states [Q₁Q₂][Q̄₃Q̄₄] ($Q=c$, b). The dynamical investigation indicates that the CMIM can not completely absorb QCD dynamical effects through the effective constituent quark mass and overestimates the color-magnetic interaction in the states under the assumption of the same spatial configurations. The Coulomb interaction plays a critical role in the dynamical model calculations on the heavy hadrons, which induces the fact that none of bound states [Q₁Q₂][Q̄₃Q̄₄] can be found in the dynamical models. The color configuration [[Q₁Q₂]_6c[Q̄₃Q̄₄]_6̄c]₁ should be taken seriously in the ground states due to the strong Coulomb attraction between the [Q₁Q₂]_6c and [Q̄₃Q̄₄]_6̄c. The color configuration [[Q₁Q₂]_3̄c[Q̄₂Q̄₄]_3c]₁ is absolutely dominant in the excited states because of the strong Coulomb attraction within the [Q₁Q₂]_3̄c and [Q̄₂Q̄₄]_3c. The J/Ψ-pair resonances recently observed by LHCb are difficult to be accommodated in the CMIM. The broad structure ranging from 6.2 to 6.8 GeV can be described as the ground tetraquark state [cc][c̄c̄] in the various dynamical models. The narrow structure $X(6900)$ can be identified as the excited state [cc][c̄c̄] with $L=1$ ($L=2$) in the constituent quark model (color flux-tube model).