Excited state baryon spectroscopy from lattice QCD

Abstract

We present a calculation of the Nucleon and Delta excited state spectra 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 $J=\frac{7}{2}$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6)\ensuremath{\bigotimes}O(3)$ representations and a counting of levels that is consistent with the nonrelativistic $qqq$ 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.