Nucleon, Δ, and Ω excited state spectra in Nf=2+1 lattice QCD
The energies of the excited states of the nucleon, Δ, and Ω are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculation is performed at three values of the light quark mass, corresponding to pion masses mπ=392(4), 438(3), and 521(3) MeV. We employ the variational method with a large basis of interpolating operators enabling six energies in each irreducible representation of the lattice to be distinguished clearly. We compare our calculation with the low-lying experimental spectrum, with which we find reasonable agreement in the pattern of states. The need to include operators that couple to the expected multihadron states in the spectrum is clearly identified.