IMPROVED Y-SPECTRUM WITH DYNAMICAL WILSON FERMIONS

We present results for the b (b) over bar spectrum obtained using an O (M(b)v(6))-correct nonrelativistic lattice QCD action, where M-b denot es the bare b-quark mass and v(2) is the mean-squared quark velocity. Propagators are evaluated on SESAM's three sets of dynamical gauge con figurations generated with two flavors of Wilson fermions at beta=5.6. These results, obtained with dynamical Wilson fermions, are compared to a quenched analysis at equivalent lattice spacing beta=6.0. Using o ur three sea-quark values, we perform the ''chiral'' extrapolation to m(eff)=m(s)/3, where m(s) denotes the strange quark mass. The light qu ark mass dependence is found to be small in relation to the statistica l errors. Comparing the full QCD result to our quenched simulation, we find better agreement of our dynamical data with experimental results in the spin-independent sector, but observe no unquenching effects in hyperfine splittings. To pin down the systematic errors we have also compared quenched results in different ''tadpole'' schemes as well as using a lower-order action. We find that spin splittings with an O(M(b )v(4)) action are O(10%) higher compared to O(M(b)v(6)) results. Relat ive to the results obtained with the plaquette method, the Landau gaug e mean-link tadpole scheme raises the spin splittings by about the sam e margin so that our two improvements are opposite in effect. [S0556-2 821(98)01307-1].