Precise determination of the Grinstein ratio of heavy-light decay constant in unquenched QCD

Abstract

We study the chiral behavior of the ratio of heavy-light decay constants on unquenched lattices with two flavor dynamical quarks using the plaquette gauge action and the nonperturbatively O(a)-improved Wilson fermion action at β = 5.2. The heavy quarks are described by the clover action and the NRQCD action. We find that the sea quark mass dependence of the decay constants largely cancels in the double ratio R 1 =f B s /f B d /f D s /f D d and the systematic error in the chiral limit can be drastically reduced. Our preliminary result with heavy clover is R 1 = 1.018 ± 0.006 ± 0.010, where the first and the second errors are the statistical and the systematics errors.