Spectroscopy of Exotic Hadrons Formed from Dynamical Diquarks

TL;DR

This paper uses the Born-Oppenheimer approximation and lattice simulation data to study the spectrum of exotic hadrons formed from dynamical diquarks, successfully matching many experimental candidates and proposing new selection rules.

Contribution

It introduces a novel application of the Born-Oppenheimer approximation to exotic hadrons with dynamical diquarks and develops a compact notation for their states.

Findings

All examined exotic candidates fit the model.

Selection rules help identify decay modes.

Including additional BO potentials improves model accuracy.

Abstract

The dynamical diquark picture asserts that exotic hadrons can be formed from widely separated colored diquark or triquark components. We use the Born-Oppenheimer (BO) approximation to study the spectrum of states thus constructed, both in the basis of diquark spins and in the basis of heavy quark-antiquark spins. We develop a compact notation for naming these states, and use the results of lattice simulations for hybrid mesons to predict the lowest expected BO potentials for both tetraquarks and pentaquarks. We then compare to the set of exotic candidates with experimentally determined quantum numbers, and find that all of them can be accommodated. Once decay modes are also considered, one can develop selection rules of both exact ($J^{PC}$ conservation) and approximate (within the context of the BO approximation) types and test their effectiveness. We find that the most appealing way to satisfy both sets of selection rules requires including additional low-lying BO potentials, a hypothesis that can be checked on the lattice.