Excited state baryon spectroscopy from lattice QCD

TL;DR

This paper calculates the excited state spectrum of nucleons and Deltas using lattice QCD, introducing a new operator method to identify continuum spins up to J=7/2, and finds results consistent with the quark model, challenging alternative models.

Contribution

It introduces a novel operator construction method enabling spin identification in lattice QCD, achieving the first spectrum of baryon states up to J=7/2 with both parities.

Findings

Spectrum includes states up to J=7/2 with both parities.

Results align with the SU(6) x O(3) quark model.

Dense spectrum contradicts quark-diquark models and shows no parity doubling.

Abstract

We present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including J = 7/2, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of SU(6) x O(3) representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.