Abstract
We review the existing results on the exotic XYZ states and their decays obtained within the confined covariant quark model. This dynamical approach is based on a non-local Lagrangian of hadrons with quarks, has built-in quark confinement, and is suited well for the description of different multiquark states, including the four quark ones. We focus our analysis on the various decay modes of five exotic states, X ( 3872 ) , Z c ( 3900 ) , Y ( 4260 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) , aiming to clarify their internal quark structures. By considering mostly branching fractions and decay widths using the molecular-type or the tetraquark-type interpolating currents, conclusions about the nature of these particles are drawn: the molecular structure is favored for Z c ( 3900 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) and the tetraquark for X ( 3872 ) and Y ( 4260 ) .
Highlights
The concept of multiquark states composed of more three quarks hypothesized decades ago [1] was for the first time confirmed in 2003 where multiquark state candidates were measured by the BES [2], BaBar [3], and Belle [4] experiments
With the aim to report on the results and achievements of the confined covariant quark model, we narrow our review of experimental outcomes to a relevant subset of the whole exotic meson family
The confined covariant quark model is an approach based on a non-local interaction Lagrangian of quarks and hadrons
Summary
The concept of multiquark states composed of more three quarks hypothesized decades ago [1] was for the first time confirmed in 2003 where multiquark state candidates were measured by the BES [2], BaBar [3], and Belle [4] experiments. We want to review the description of the exotic heavy quarkonia-like states by the confined covariant quark model (CCQM). The model [67,68,69] was proposed and developed as a practical and reliable tool for the theoretical description of exclusive reactions involving the mesons, baryons, and other multiquark states It was based on a non-local interaction Lagrangian, which introduces a coupling between a hadron and its constituent quarks. A confinement was not implemented in the model, and it was not suited for heavy particles (with baryon mass exceeding those of the constituent quarks summed) This was changed in [69], where a smart cutoff was introduced for integration over the space of Schwinger parameters.
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