Deciphering the recently discovered tetraquark candidates around 6.9 GeV

Recently a novel hadronic state of mass 6.9 GeV, that decays mainly to a pair of charmonia, was observed in LHCb. The data also reveals a broader structure centered around 6490 MeV and suggests another unconfirmed resonance centered at around 7240 MeV, very near to the threshold of two doubly charmed Xi cc baryons. We argue in this note that these exotic hadrons are genuine tetraquarks and not molecules of charmonia. It is conjectured that they are V-baryonium , namely, have an inner structure of a baryonic vertex with a cc diquark attached to it, which is connected by a string to an anti-baryonic vertex with a cc anti-diquark. We examine these states as the analogs of the V-baryonium states Psi (4360) and Y(4630)/Psi (4660) which are charmonium-like tetraquarks. One way to test these claims is by searching for a significant decay of the state at 7.2 GeV into Xi ccXi cc. Such a decay would be the analog of the decay of the state Y(4630) into to Lambda cLambda c. We further argue that there should be trajectories of both orbital and radial excited states of the X(6900). We predict their masses. It is possible that a few of these states have already been seen by LHCb.

Automated summary

A novel hadronic state with a mass of 6.9 GeV discovered by LHCb decays mainly to a pair of charmonia, while data also suggests the presence of broader structures and unconfirmed resonances. It is argued that these exotic hadrons are tetraquarks with a V-baryonium structure, and the need for further research and testing for the decay of the state at 7.2 GeV into Xi ccXi cc is emphasized.