Interpretation of structure in the di-J/Ψ spectrum

Structure in the di-J/Ψ mass spectrum observed by the LHCb experiment around 6.9 and 7.2 GeV is interpreted in terms of JPC=0⁺⁺ and 2⁺⁺ resonances between a $cc$ diquark and a c̄c̄ antidiquark, using a recently confirmed string-junction picture to calculate tetraquark masses. The main peak around 6.9 GeV is likely dominated by the 0⁺⁺(2S) state, a radial excitation of the cc-c̄c̄ tetraquark, which we predict at $6.871±0.025$ $GeV$. The dip around 6.75 GeV is ascribed to the opening of the S-wave di-χc0 channel, while the dip around 7.2 GeV could be correlated with the opening of the di-ηc(2S) or ΞccΞcc channel. The low-mass part of the di-J/Ψ structure appears to require a broad resonance consistent with a predicted 2⁺⁺(1S) state with invariant mass around Mᵢₙᵥ=6400 $MeV$. Implications for bbb̄b̄ tetraquarks are discussed.