Strong decays of fully-charm tetraquarks into di-charmonia.

We study strong decays of the possible fully-charm tetraquarks recently observed by LHCb, and calculate their relative branching ratios through the Fierz rearrangement. Together with our previous QCD sum rule study, our results suggest that the broad structure around 6.2-6.8 GeV can be interpreted as an S-wave ccc¯c¯ tetraquark state with J=0 or 2, and the narrow structure around 6.9 GeV can be interpreted as a P-wave one with J=0 or 1. These structures were observed in the di-J/ψ invariant mass spectrum, and we propose to confirm them in the di-η,J/ψh,ηχ, and ηχ channels. We also propose to search for their partner states having the negative charge-conjugation parity in the J/ψη,J/ψχ,J/ψχ, and ηh channels.