On the proliferation of X's, Y's and Z's candidates

TL;DR

This paper investigates how threshold effects influence heavy meson spectroscopy across various flavor sectors, examining the compatibility of quark models with potential multiquark structures and molecular states.

Contribution

It provides a comparative analysis of threshold impacts on heavy meson spectra, challenging the validity of quark models above open-flavor thresholds.

Findings

Threshold effects significantly alter meson resonance interpretations.

Quark models may be limited in describing states above open-flavor thresholds.

Multiquark and molecular structures are constrained by threshold considerations.

Abstract

Heavy meson spectroscopy above open flavor thresholds has become a challenge both from the experimental and theoretical points of view. Experimentally, several signals have been interpreted as meson resonances with unusual properties; theoretically, such signals may be identified with meson-meson molecules or compact multiquark structures. We analyze the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge multiquark structures as meson-meson molecules.