Excited state nucleon spectrum with two flavors of dynamical fermions

Highly excited states for isospin 1/2 baryons are calculated for the first time using lattice QCD with two flavors of dynamical quarks. Anisotropic lattices are used with two pion masses, m_π=416(36)   MeV and 578(29) MeV. The lowest four energies are reported in each of the six irreducible representations of the octahedral group at each pion mass. The lattices used have dimensions 24³×64, spatial lattice spacing a_s≈0.11  fm, and temporal lattice spacing a_t=1/3a_s. Clear evidence is found for a 5^-/2 state in the pattern of negative-parity excited states. This agrees with the pattern of physical states and spin 5/2 has been realized for the first time on the lattice.