Spectroscopy of B s and D s Mesons ∗

There are several ways of approximating heavy quarks in lattice QCD calculations, including Nonrelativistic QCD [1–3] (NRQCD), the static approximation [4,5], and the approach developed at Fermilab [6] which takes the uncorrected Wilson action as its leading approximation but adds correction operators which end up resembling those of NRQCD rather than those of the standard Symanzik improvement of the Wilson action [7]. NRQCD is based on an expansion in nonrelativistic operators (rotationally invariant but not Lorentz invariant) similar to that used in calculating relativistic corrections in the hydrogen atom. It can be thought of as arising from a discretization of the action arising from a FoldyWouthuysen-Tani transformation of the quark fields analogous to the one used in atomic physics.