Dynamical picture for the exotic XYZ states

TL;DR

This paper develops a dynamical approach to describe exotic multi-quark states like X(3872), Zc(3900), Zb(10610), and Zb(10650), analyzing their decay properties and testing tetraquark versus molecular models against experimental data.

Contribution

It introduces a dynamical framework using effective interaction Lagrangians to analyze multi-quark states and compares tetraquark and molecular descriptions for specific exotic mesons.

Findings

X(3872) decay widths align with experimental data for reasonable size parameters.

Tetraquark model for Zc(3900) predicts decay patterns inconsistent with experiments.

Molecular-type currents for Zc(3900) match observed decay behaviors.

Abstract

We present a dynamical approach for description of the multi-quark states that is based on an effective interaction Lagrangian describing the coupling of hadrons to their constituent quarks. First, we explore the consequences of treating the $X(3872)$ meson as a tetraquark bound state. We calculate the decay widths of the observed channels and conclude that for reasonable values of the size parameter of the $X(3872)$ one finds consistency with the available experimental data. Then we have critically checked the tetraquark picture for the $Z_c(3900)$ state by analyzing its strong decays. We found that $Z_c(3900)$ has a much more stronger coupling to $DD^\ast$ than to $J/\psi\pi$ that is in discord with experiment. As an alternative we have employed a molecular-type four-quark current to describe the decays of the $Z_c(3900)$ state as the charged particle in the isotriplet. We found that a molecular-type current gives the values of the above decays in accordance with the experimental observation. By using molecular-type four-quark currents for the recently observed resonances $Z_b(10610)$ and $Z_b(10650)$, we have calculated their two-body decay rates into a bottomonium state plus a light meson as well as into B-meson pairs.