Investigating the internal structure of $X(6900)$ in the $2J\mathrm{/}\psi$ decay channel

Assuming $X(6900)$ is a tetraquark state, the decay width of $X(6900)\to 2J\mathrm{/}\psi$ is calculated in a covariant quark model, with the diquark-antidiquark $[cc][\bar{c}\bar{c}]$ picture. Two possible structures, vector-vector and axial-vector–axial-vector coupling, are investigated. The result indicates that the axial-vector–axial-vector coupling is consistent with the experiments. Additionally, as another application of the covariant quark model, the decay width of $X(6900)\to 2{\eta }_c$ is predicted to be $66\sim 88$ keV.