A study of O(1/m_{Q}²) corrections for f_{B} with lattice NRQCD

We investigate higher order effects in the nonrelativistic expansion of lattice QCD on the heavy-light meson decay constants and some other quantities in order to understand the truncation error of NRQCD. While our numerical results have large $O(a)$ and $O(\alpha_s)$ errors due to the use of Wilson light quark action and the tree-level matching, we find that the truncation error of higher order relativistic corrections are adequately small around the mass of the $b$ quark. We also present a perturbatively matched results through 1-loop level without operator mixing effects.