Light hadron spectroscopy with two flavors of O(a)-improved dynamical quarks -: art. no. 054502

We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at beta=5.2, where the lattice spacing is found to be a=0.0887(11) fm from the rho meson mass, on a 20(3)x48 lattice. At each of five sea quark masses corresponding to m(PS)/m(V)similar or equal to0.8-0.6, we generate 12 000 trajectories using a symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 12(3)x48, 16(3)x48 lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find m(ud)((MS) over bar)(2 GeV)=3.223((+0.046)(-0.069)) MeV and m(s)((NS) over bar)(2 GeV)=84.5((+12.0)(-1.7)) MeV which are about 20% smaller than in quenched QCD.