Heavy-light decay constants for B and D mesons in nf = 2 unquenched QCD in Fermilab formalism

Abstract

Abstract We report our calculation of the heavy-light decay constants f B and f D on a 20 3 × 48 lattice at β = 5.2 with n f = 2 sea quarks by the fully 0(a)-improved Wilson fermion and heavy quarks in Fermilab formalism. We find that the B meson decay constants are consistent with those obtained with the NRQCD formalism. It is shown that the quark mass dependence almost cancels in the B/D ratio of the decay constant so that the systematic errors in the chiral extrapolation can be reduced. Taking the Grinstein ratio, remaining uncertainties from the perturbation and discretization also cancel to give a precise prediction of ( f B s f B d ) ( f D s f D d ) of 1% accuracy.