Excited State Nucleon Spectrum With Two Flavors Of Dynamical Fermions PDF Download

Excited states for isospin $\frac{1}{2}$ baryons are calculated using lattice QCD with two flavors of dynamical quarks. Anisotropic lattices are used with two pion masses, $m_{\pi} = 416(36)$~MeV and $578(29)$~MeV. A large number of baryon operators is developed. They are pruned to sets of 16 and a variational analysis is carried out for $16\times 16$ matrices of correlation functions. 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 $24^3\times 64$, spatial lattice spacing $a_s \approx 0.11$~fm and temporal lattice spacing $a_t = \frac{1}{3} a_s$. Clear evidence is found for a $\frac{5}{2}^-$ state in the pattern of negative-parity excited states. This agrees with the pattern of physical states and spin $\frac{5}{2}$ has been realized for the first time on the lattice.