High-Precision Lattice QCD Confronts Experiment

The recently developed Symanzik-improved staggered-quark discretization allows unquenched lattice-QCD simulations with much smaller (and more realistic) quark masses than previously possible. To test this formalism, we compare experiment with a variety of nonperturbative calculations in QCD drawn from a restricted set of “gold-plated” quantities. We find agreement to within statistical and systematic errors of $3\%$ or less. We discuss the implications for phenomenology and, in particular, for heavy-quark physics.