Molecular structures in charmonium spectrum: The $XYZ$ puzzle

TL;DR

This paper investigates the role of molecular structures in the charmonium spectrum, particularly the XYZ states, using a constituent quark model to analyze both quark-antiquark and molecular components.

Contribution

It introduces a formalism that simultaneously considers quark-antiquark and molecular structures across thresholds, providing new insights into the nature of XYZ states.

Findings

X(3872) is identified as a molecular state.

Y(3940) and X(3915) are suggested to be conventional charmonium states.

Molecular contributions significantly influence the phenomenology of certain states.

Abstract

We study in the framework of a constituent quark model the possible contributions of molecular structures to the XYZ charmonium like states. We analyze simultaneously the $c\bar{c}$ structures and the possible molecular components in a formalism which allows us to treat channels below and above thresholds. The only molecular state found in the $1^{++}$ sector correspond to the X(3872). Molecular resonances also appear with other quantum numbers. So, the so called Y(3940) and the X(3915) are suggested to be $J^{PC}=0^{++}$ charmonium states. In the $J^{PC}=1^{--}$ sector we also found significant contributions of the molecular structures which can affect the phenomenology.