Light 1-+ exotics: molecular resonances

TL;DR

This paper presents a theoretical study supporting the idea that certain exotic mesons are tetraquark molecular resonances, providing calculations and tools to distinguish these states from hybrids and guiding future experiments.

Contribution

The authors develop a QCD-inspired model calculation that favors molecular tetraquark resonances over hybrid or other exotic configurations, and propose experimental correlators for identification.

Findings

Molecular-like configurations are favored over hybrid states.

The model supports the existence of tetraquark molecular resonances.

A useful off-plane correlator is proposed for experimental identification.

Abstract

Highlights in the search for nonconventional (non qqbar) meson states are the pi_1(1400) and pi_1(1600) exotic candidates. Should they exist, mounting theoretical arguments suggest that they are tetraquark molecular resonances excitable by meson rescattering. We report a new tetraquark calculation within a model field theory approximation to Quantum Chromodynamics in the Coulomb gauge supporting this conjecture. We also strengthen this claim by consistently contrasting results with exotic state predictions for hybrid (q qbar g) mesons within the same theoretical framework. Our findings confirm that molecular-like configurations involving two color singlets (a resonance, not a bound state) are clearly favored over hybrid or color-exotic tetraquark meson (q qbar q qbar atoms) formation. Finally, to assist needed further experimental searches we document a useful off-plane correlator for establishing the structure of these exotic systems along with similar, but anticipated much narrower, states that should exist in the charmonium and bottomonium spectra.