Dynamical Approach to Decays of XYZ States

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 ) .

B Meson Decays in the Covariant Confined Quark Model

“…Finally, we have to mention that the CCQM is suitable for description of various multi-quark states, including baryons [46,47] and tetraquarks [48]. In this text, we focus on mesons; the approach is, in other cases, very similar: the interpolating quark current is constructed for a given number of quarks (more alternatives can be considered) and multiplied by the hadronic field to provide the interaction Lagrangian.…”

“…They often have a larger number of hadrons in the final state (three or more) and, thus, large phase space and technically complicated description. The exotic particles are usually treated in the scenario where they represent the initial state (for the CCQM model, see [48]) and, thus, are not in the scope of this text (i.e., they are not B mesons). The emphasis of the theoretical overview is, therefore, on the remaining topics: branching fractions and weak-interaction physics.…”

Rare $b \to d$ decays in covariant confined quark model

“…[55,67,68]. CCQM is a versatile quark model capable for studying the hadronic interaction of multiquark state also and has been recently utilised for computing various decay properties of D, D s and B c mesons [68][69][70][71][72][73], baryons [74][75][76][77] and exotic states [78][79][80][81][82][83]. In Fig.…”