Finite-size and quark mass effects on the QCD spectrum with two flavors

We have carried out spectrum calculations with two flavors of dynamical Kogut-Susskind quarks on four lattice sizes from $8^3\times 24$ to $16^3\times24$ at couplings that correspond to chiral symmetry restoration for a lattice with 6 time slices. We estimate that the linear spatial sizes of the lattices range from 1.8 to 3.6 fm. We find significant finite size effects for all particles between the smallest and largest volume with the larger quark mass that we study, $am_q=0.025$, where $a$ is the lattice spacing. The nucleon experiences the largest effect of about 6 percent. We also study a lighter quark mass, $am_q=0.0125$, on the two largest lattices. Effects of the dynamical and valence quark masses on the hadron spectrum are studied both directly, by comparing the two simulations, and by extracting mass derivatives from the correlation functions. We do not find much improvement in the nucleon to rho mass ratio as we decrease the quark mass at this lattice spacing. Finally, we report on an unsuccessful attempt to see effects of the $\rho \rightarrow 2\pi$ decay on the $\rho$ mass, and on studies of Wilson and Kogut-Susskind hadron masses with large valence quark masses. (The paper is also available via anonymous ftp in a compressed PostScript file: fuji.physics.indiana.edu:/pub/milc/paper.ps.Z .)