Deciphering the recently discovered tetraquark candidates around 6.9 GeV

TL;DR

This paper investigates the nature of recently observed 6.9 GeV tetraquark candidates, proposing they are genuine tetraquarks with specific internal structures, and predicts their excited states and decay behaviors.

Contribution

It introduces a novel interpretation of the 6.9 GeV states as V-baryonium tetraquarks with specific internal structures, and predicts their excited states and decay channels.

Findings

The 6.9 GeV states are likely genuine tetraquarks, not molecular states.

Predicted trajectories and masses for excited states of the 6900 MeV tetraquark.

Possible existing observations of some predicted states by LHCb.

Abstract

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 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 $Y(4630)$/$\Psi(4660)$ 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 $\Xi_{cc}\overline\Xi_{cc}$. Such a decay would be the analog of the decay of the state $Y(4630)$ into to $\Lambda_c\overline\Lambda_c$. 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.