Heavy Tetraquarks in the Relativistic Quark Model

Rudolf N Faustov,Vladimir O Galkin,Elena M Savchenko

doi:10.3390/universe7040094

Abstract

We give a review of the calculations of the masses of tetraquarks with two and four heavy quarks in the framework of the relativistic quark model based on the quasipotential approach and QCD. The diquark-antidiquark picture of heavy tetraquarks is used. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Diquarks are considered in the colour triplet state. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole and the internal structure of the diquarks is taken into account by the calculated form factor of the diquark-gluon interaction. All parameters of the model are kept fixed from our previous calculations of meson and baryon properties. A detailed comparison of the obtained predictions for heavy tetraquark masses with available experimental data is given. Many candidates for tetraquarks are found. It is argued that the structures in the di-J/ψ mass spectrum observed recently by the LHCb collaboration can be interpreted as ccc¯c¯ tetraquarks.

Highlights

The possibility of the existence of exotic multiquark hadrons, with the content of the valence quarks and antiquarks being different from a quark–antiquark pair for mesons, and three quarks for baryons, had been considered since the early days of the quark model.the absence of convincing experimental evidence for such multiquark state made investigation of marginal interest for several decades
Significantly different interpretations for the qqqqcandidates were proposed: molecules composed from two mesons loosely bound by the meson exchange, compact tetraquarks composed from a diquark and antidiquark bound by strong forces, hadroquarkonia composed of a heavy quarkonium embedded in a light meson, kinematic cusps, etc
All considerations are performed in the framework of the relativistic quark model based on the quasipotential approach, QCD and the diquark–antidiquark picture

Summary

Introduction

The possibility of the existence of exotic multiquark hadrons, with the content of the valence quarks and antiquarks being different from a quark–antiquark pair for mesons, and three quarks for baryons, had been considered since the early days of the quark model. Heavy tetraquarks are of particular interest, since the presence of a heavy quark increases the binding energy of the bound system and, as a result, the possibility that such tetraquarks will have masses below the thresholds for decays to mesons with open heavy flavour. A tetraquark is considered as the dd0 bound state where constituents are assumed to interact as a whole This means that there are no separate interactions between quarks, composing a diquark, and antiquarks, composing an antidiquark [14]. These tetraquarks are explicitly exotic, with heavy flavor number equal to 2 Their observation would be a direct proof of the existence of multiquark states. We considered heavy (cq)(bq0 ) tetraquark (q, q0 = u, d, s) as the bound system of the heavy–light diquark (cq) and heavy–light antidiquark (bq0 ); QQ Q Qtetraquarks composed from heavy (Q = c, b) quarks only [23]. We considered heavy ( QQ0 )( Q Q0 ) tetraquark as the bound system of the doubly heavy diquark (QQ0 ) and doubly heavy antidiquark (Q Q0 )

Relativistic Diquark–Antidiquark Model of Heavy Tetraquarks

QQ Q Q Tetraquarks

Conclusions