Tetraquark candidates in LHCb's di-J/ψ mass spectrum

In this article, we study the first radial excited states of the scalar, axialvector, vector, and tensor diquark-antidiquark-type cc (c) over bar(c) over bar tetraquark states with the QCD sum rules and obtain the masses and pole residues; then, we use the Regge trajectories to obtain the masses of the second radial excited states. The predicted masses support assigning the broad structure from 6.2 to 6.8 GeV in the di-J/psi mass spectrum to be the first radial excited state of the scalar, axialvector, vector, or tensor cc (c) over bar(c) over bar tetraquark state, as well as assigning the narrow structure at about 6.9 GeV in the di-J/psi mass spectrum to be the second radial excited state of the scalar or axialvector cc (c) over bar(c) over bar tetraquark state.