# Are the XYZ states unconventional states or conventional states with unconventional properties?

## TL;DR

This paper explores three theoretical scenarios for interpreting heavy quark mesons near decay thresholds, analyzing whether they are conventional quark-antiquark states or have unconventional properties, with implications for experimental observations.

## Contribution

It compares three distinct models for heavy quark mesons near thresholds, clarifying their differences and potential experimental signatures.

## Key findings

- Different models predict distinct meson spectra and properties.
- Threshold effects significantly influence meson characteristics.
- Experimental data can distinguish between the proposed scenarios.

## Abstract

We discuss three possible scenarios for the interpretation of mesons containing a heavy quark and its antiquark near and above the first threshold for a decay into a pair of heavy mesons in a relative $S$--wave. View I assumes that these thresholds force the quark potential to flatten which implies that while in these energy ranges molecular states may be formed there should not be any quark--anti-quark states above these thresholds. View II assumes that the main part of the interaction between two mesons is due to the poles which originate from the $Q\bar Q$ interaction. The properties of the $Q\bar Q$ mesons are strongly influenced by opening thresholds but the number of states is given by the quark model. In View III, both types of mesons are admitted also near and above the open flavor thresholds: $Q\bar Q$ mesons and dynamically generated mesons. Experimental consequences of these different views are discussed.