Pentaquark and Tetraquark states

Abstract

The past seventeen years have witnessed tremendous progress on the experimental and theoretical explorations of the multiquark states. The hidden-charm and hidden-bottom multiquark systems were reviewed extensively in Ref. [1]. In this article, we shall update the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years. Especially the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks but also provided strong evidence of the molecular picture. Besides the well-known XY Z and P c states, we shall discuss more interesting tetraquark and pentaquark systems either with one, two, three or even four heavy quarks. Some very intriguing states include the fully heavy exotic tetraquark states QQ Q Q and doubly heavy tetraquark states QQq q, where Q is a heavy quark. The QQ Q Q states may be produced at LHC while the QQq q system may be searched for at BelleII and LHCb. Moreover, we shall pay special attention to various theoretical schemes such as the chromomagnetic interaction (CMI), constituent quark model, meson exchange model, heavy quark and heavy diquark symmetry, QCD sum rules, Faddeev equation for the three body systems, Skyrme model and the chiral quark-soliton model, and the lattice QCD simulations. We shall emphasize the model-independent predictions of various models which are truly/closely related to Quantum Chromodynamics (QCD). For example, the chromomagnetic interaction arises from the gluon exchange which is fundamental and universal in QCD and responsible for the mixing and mass splitting of the conventional mesons and baryons within the same multiplet. The same CMI

The lineshape of the compact fully heavy tetraquark

“…Refs. [6,20,44] further include the chromoelectro and chromomagnetic interaction and find that these two kinds of interaction cannot be neglected to obtain the correct spectrum. Among them, our method is similar to that in Ref.…”

“…That challenges the conventional quark model and stimulates research enthusiasm on the so called exotic hadrons. Up to now, tens of exotic candidates have been observed by experimental collaborations (such as LHCb, BESIII, BelleII, JLab, CMS, ATLAS) and numerous studies [1][2][3][4][5][6][7][8][9][10] have been proposed for the understanding of their properties.…”

Exotic ΩΩ dibaryon states in a molecular picture *

“…The history of multiquark configurations can go back to the establishment of the quark model (QM) by Gell-Mann [1] and Zweig [2], where the tetraquark qq q q and pentaquark qqqq q configurations were proposed outside of the conventional meson and baryon states. In the past seventeen years, there have been great progress on the explorations of tetraquark and pentaquark states, with the observations of the so called XYZ and P c states [3][4][5][6][7][8][9][10].…”

Prompt production of the hidden charm pentaquarks in the LHC

“…As the mass of the D * s0 (2317) is significantly lower than its quark model expectation and the quantum number of the X(3872) does not fit into the quark mode, they both seriously challenged the conventional quark model and served as strong candidates for the exotic states. Up to now, tens of exotic candidates [4,5] have been observed and various proposals were put forward about their configurations from theoretical side [6][7][8][9][10][11][12][13][14][15][16].…”