Excited nucleon spectrum using a non-perturbatively improved clover fermion action

TL;DR

This paper presents lattice QCD calculations of negative-parity baryon masses using an improved fermion action, analyzing finite-volume and lattice-spacing effects, and comparing results with experimental data.

Contribution

It provides the first quenched lattice QCD determination of negative-parity baryon masses with an ${ m O}(a)$-improved clover action, including systematic uncertainty analysis.

Findings

Negative-parity nucleon mass computed and split from the ground state.

First excited nucleon radial excitation mass found larger than negative-parity ground state.

Results for negative-parity $I=3/2$ state also presented.

Abstract

We discuss the extraction of negative-parity baryon masses from lattice QCD calculations. The mass of the lowest-lying negative-parity $J = 1/2^{-}$ state is computed in quenched lattice QCD using an ${\cal O}(a)$-improved clover fermion action, and a splitting found with the nucleon mass. The calculation is performed on two lattice volumes, and three lattice spacings enabling a study of both finite-volume and finite-lattice-spacing uncertainties. A measurement of the first excited radial excitation of the nucleon finds a mass considerably larger than that of the negative-parity ground state, in accord with other lattice determinations but in disagreement with experiment. Results are also presented for the lightest negative-parity $I=3/2$ state.