Excited baryon spectroscopy from lattice QCD: Finite size effect and hyperfine mass splitting

A study of the finite-size effect is carried out for spectra of both ground-state and excited-state baryons in quenched lattice QCD using Wilson fermions. Our simulations are performed at β=6/g²=6.2 with three different spatial sizes, La~ 1.6, 2.2 and 3.2 fm. It is found that the physical lattice size larger than 3 fm is required for Δ states in all spin-parity (JP=1/2^±,3/2^±) channels and also negative-parity nucleon (N*) state (JP=1/2^-) even in the rather heavy quark mass region (M_π~1.0 GeV). We also find a peculiar behavior of the finite-size effect on the hyperfine mass splittings between the nucleon and the Δ in both parity channels.