We introduce an alternative discretization for static quarks on the lattice retaining the O(a) improvement properties of the Eichten-Hill action. In this formulation, statistical fluctuations are reduced by a factor which grows exponentially with Euclidean time, x_0. For the first time, B-meson correlation functions are computed with good statistical precision in the static approximation for x_0>1 fm. At lattice spacings a \approx 0.1 fm, a \approx 0.08 fm and a \approx 0.07 fm the B_s-meson decay constant is determined in static and quenched approximations. A correction due to the finite mass of the b-quark is estimated by combining these static results with a recent determination of F_Ds.
Bibliographical noteEqs. 14 and 15 corrected. Changes by up to 1 sigma in Table 1, Eq. 22 changed consequently. Result in Eq. 24 unchanged
Morte, M. D., Durr, S., Heitger, J., Molke, H., Rolf, J., Shindler, A., & Sommer, R. (2003). Lattice HQET with exponentially improved statistical precision. Phys.Lett.B. https://doi.org/10.1016/j.physletb.2005.03.017