Hadron masses with two quark flavors

We investigate the hadron mass spectrum in lattice QCD with two flavors of dynamical quarks. We use $6^3$×24, $8^3$×24, and ${10}^3$×24 lattices with 6/$g^2$ adjusted so that the thermal crossover temperature is 1/4a or 1/6a. At these values of 6/$g^2$ flavor symmetry is not restored and the familiar problem of the nucleon to ρ mass ratio is not fixed by the dynamical fermions. For comparison and checking we measure the spectrum in the quenched approximation using analogous couplings and identical methods. The effects of the finite spatial size are investigated and found to be small. We discuss our fitting procedures and our control of systematic errors in some detail. We combine our mass measurements with previous calculations to estimate the temperature for the transition to a chirally symmetric phase of QCD in physical units.