Lattice baryon spectroscopy with multi-particle interpolators

TL;DR

This paper investigates the nucleon spectrum in lattice QCD using multi-particle interpolators, revealing insights into excited states and the robustness of spectral extraction methods.

Contribution

It introduces the use of local meson-baryon and five-quark operators in lattice QCD to improve nucleon excited state spectroscopy.

Findings

Observation of a state near the S-wave Nπ scattering threshold in negative parity

Robustness of the variational technique across different operator bases

Consistent low-lying spectrum energies despite basis variations

Abstract

In 2 + 1 flavour 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 consistent with the 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.