Hydrogen bond of QCD

Luciano Maiani,Veronica Riquer,Antonio D. Polosa

doi:10.1103/physrevd.100.014002

Luciano Maiani, Veronica Riquer + Show 1 more

Open Access

https://doi.org/10.1103/physrevd.100.014002

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Abstract

Using the Born-Oppenheimer approximation, we show that exotic resonances, X and Z, may emerge as QCD molecular objects made of colored two-quark lumps, states with heavy-light diquarks spatially separated from antidiquarks. With the same method we confirm that doubly heavy tetraquarks are stable against strong decays. Tetraquarks described here provide a new picture of exotic hadrons, as formed by the QCD analog of the hydrogen bond of molecular physics.

Highlights

In this paper we present a description of tetraquarks [1,2,3] in terms of color molecules: two lumps of two-quark held together by color forces
We restrict to heavy-light systems, QQqqor QQqq, and apply the Born-Oppenheimer (BO) approximation, see e.g., [4], the method used for the hydrogen molecule, see [5]
The method consists in solving the eigenvalue problem for the light particles with fixed coordinates of the heavy ones, xA, xB, and solve the Schrödinger equation of the heavy particles in the BO potential

Summary

INTRODUCTION

In this paper we present a description of tetraquarks [1,2,3] in terms of color molecules: two lumps of two-quark (colored atoms) held together by color forces. We obtain color repulsion within the heavy QQand the light qqquark pairs, and mutual attraction between heavy and light quarks or antiquarks. Increasing the repulsion between light quarks beyond the naive one-gluon exchange force, we obtain a configuration of the potential which separates the diquarks from each other, Fig. 1(b), as envisaged in [20], with the phenomenological implications discussed in [10] and [21]. At large separations between heavy quarks the lowest state will correspond to a pair of color singlet charmed mesons. We hope that our approach may be the basis of further investigations on the internal structure of multiquark hadrons and the phenomenology of their decays Nonperturbative investigations along these lines should be provided by lattice QCD (see for example [6]), following the growing interest shown for doubly heavy tetraquarks [22]. It gives an independent thrust to the idea of stable bbqq ̄ tetraquarks, still awaiting an experimental confirmation

HIDDEN CHARM

The cq orbital

BO ðrAB Þ

BO δE: ð19Þ

DOUBLE BEAUTY TETRAQUARKS: bb IN 6