Deciphering the recently discovered tetraquark candidates around 6.9 GeV

Abstract

AbstractRecently 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 $$\Xi _{cc}$$ Ξ 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 $${\bar{c}} {\bar{c}}$$ c ¯ c ¯ anti-diquark. We examine these states as the analogs of the V-baryonium states $$\Psi (4360)$$ Ψ ( 4360 ) and Y(4630)/$$\Psi (4660)$$ Ψ ( 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 $$\Xi _{cc}{\overline{\Xi }}_{cc}$$ Ξ cc Ξ ¯ cc . Such a decay would be the analog of the decay of the state Y(4630) into to $$\Lambda _c{\overline{\Lambda }}_c$$ Λ c Λ ¯ 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.