Lattice baryon spectroscopy with multiparticle interpolators

In 2 + 1 flavor lattice QCD, the spectrum of the nucleon is presented for both parities using local meson-baryon-type interpolating fields in addition to the standard three-quark nucleon interpolators. The role of local five-quark operators in extracting the nucleon excited-state spectrum via correlation matrix techniques is explored on dynamical gauge fields with m(pi) = 293 MeV, leading to the observation of a state in the region of the noninteracting S-wave N pi scattering threshold in the negative-parity sector. Furthermore, the robustness of the variational technique is examined by studying the spectrum on a variety of operator bases. Fitting a single-state ansatz to the eigenstate-projected correlators provides robust energies for the low-lying spectrum that are essentially invariant despite being extracted from qualitatively different bases.