Why quarkonium hybrid coupling to two S-wave heavy-light mesons is not suppressed

TL;DR

This paper demonstrates that quarkonium hybrids can decay into pairs of S-wave heavy-light mesons via string breaking, challenging previous assumptions and deriving new selection rules consistent with lattice QCD results.

Contribution

It introduces model-independent selection rules for hybrid meson decays, showing that certain couplings are not suppressed as previously thought.

Findings

The $ ext{Σ}_u^-$ potential couples to S-wave meson pairs via string breaking.

The $ ext{Π}_u$ potential does not couple to S-wave meson pairs.

Selection rules derived are consistent with lattice QCD decay widths.

Abstract

We examine the couplings of quarkonium hybrids to heavy-light meson pairs in the Born-Oppenheimer approximation for QCD. The lowest hybrid multiplets consist of bound states of the $\Pi_u$ and $\Sigma_u^-$ potentials. We find that the $\Sigma_u^-$ potential can couple to pairs of $S$-wave mesons through string breaking, while the $\Pi_u$ potential cannot. From this observation, we derive model-independent selection rules that contradict previous expectations that quarkonium hybrids are forbidden to decay into pairs of $S$-wave mesons. These Born-Oppenheimer selection rules are consistent with the partial decay widths of the lowest charmonium hybrid with exotic quantum numbers $J^{PC}=1^{-+}$ recently calculated in lattice QCD.