Computation of the heavy-light decay constant using nonrelativistic lattice QCD

We report results on a lattice calculation of the heavy-light meson decay constant employing the nonrelativistic QCD approach for heavy quarks and the Wilson action for light quarks. Simulations are carried out at β=6.0 on a 16×48 lattice. The signal to noise ratio for the ground state is significantly improved compared to simulations in the static approximation, enabling us to extract the decay constant reliably. We compute the heavy-light decay constant for several values of heavy quark mas and estimate the magntiude of the deviation from the heavy mass scaling law ${\mathit{f}}_{\mathit{P}}$ √${\mathit{m}}_{\mathit{P}}$ =const. For the B meson we find ${\mathit{f}}_{\mathit{B}}$=171±${22}_{\mathrm{-}45}^{+19\mathrm{}}$ MeV, while an extrapolation to the static limit yields ${\mathit{f}}_{\mathit{B}}^{\mathrm{static}}$=297±${36}_{\mathrm{-}30}^{+15\mathrm{}}$ MeV.