Ordering of spin-12 excitations of the nucleon in lattice QCD

We present results for the negative parity low-lying state of the nucleon, N12− (1535 MeV) S11, from a variational analysis method. The analysis is performed in quenched QCD with the FLIC fermion action. The principal focus of this Letter is to explore the level ordering between the Roper (P11) and the negative parity ground (S11) states of the nucleon. Evidence of the physical level ordering is observed at light quark masses. A wide variety of smeared-smeared correlation functions are used to construct correlation matrices. A comprehensive correlation matrix analysis is performed to ensure an accurate isolation of the N12− state.