Unexpected Mesons X, Y, Z, ... (tetraquarks? hadron molecules? ...)

TL;DR

This paper discusses recent meson resonances, proposing they are best described as multi-component Fock states combining quark-antiquark pairs and meson-antimeson pairs, rather than solely tetraquarks or molecules.

Contribution

It introduces a novel interpretation of meson resonances as multi-component Fock states using the energy-time uncertainty relation.

Findings

Resonances may be superpositions of quark-antiquark and meson-antimeson states.

Decay properties can reveal different Fock components.

This approach offers a new perspective on meson structure.

Abstract

This talk briefly discusses the set of meson resonances discovered in the latest decade. They are frequently treated in the literature as tetraquarks or hadron molecules. Our consideration (using the energy-time uncertainty relation) suggests, however, that the most reasonable description for each of them may be a two- (or more-) component Fock column, with one line being a conventional quark-antiquark pair, and the other line(s) corresponding to a charmed (or beauty) meson-antimeson pair near its threshold. Detailed investigation of decay properties might allow to reveal presence of several Fock components and separate their contributions.