Deciphering the recently discovered tetraquark candidates around 6.9 GeV

Abstract

Recently a novel hadronic state of mass 6.9 GeV, that decays mainly to a pair of charmonina, 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 tetraquarks, 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 \(\bar c \bar c\) anti-diquark. We examine these states as the analogs of the states \(\Psi(4360)\) and \(Y(4630)\) which are charmonium-like tetraquarks. A simple method to test these claims is by searching for a significant decay of the state at 7.2 GeV into \(\Xi_{cc}\bar{\Xi}_{cc}\). Such a decay would be the analog of the decay of the state \(Y(4630)\) into to \(\Lambda_c\bar\Lambda_c\). 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.