The Flavor Structure of the Excited Baryon Spectra from Lattice QCD

TL;DR

This paper uses lattice QCD to compute the excited state spectra of various baryons, revealing their flavor and spin structures and identifying hybrid states with chromo-magnetic dominance.

Contribution

It constructs baryonic operators based on continuum symmetries and calculates correlation matrices to extract detailed excited state spectra up to J=7/2.

Findings

Spectra show bands with well-defined spins up to J=7/2.

States reflect SU(6)×O(3) symmetry in flavor and spin.

Hybrid states identified via chromo-magnetic operator dominance.

Abstract

Excited state spectra are calculated using lattice QCD for baryons that can be formed from $u$, $d$ and $s$ quarks, namely the $N$, $\Delta$, $\Lambda$, $\Sigma$, $\Xi$ and $\Omega$ families of baryons. Baryonic operators are constructed from continuum operators that transform as irreducible representations of SU(3)$_F$ symmetry for flavor, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Covariant derivatives are used to realize orbital angular momenta. Using the operators, we calculate matrices of correlation functions in order to extract excited states. The resulting lattice spectra have bands of baryonic states with well-defined total spins up to $J=7/2$. Each state can be assigned a dominant flavor symmetry and the counting of states of each flavor and spin reflects $SU(6) \times O(3)$ symmetry for the lowest negative-parity and positive-parity bands. States with strong hybrid content are identified through the dominance of chromo-magnetic operators.