HQET at order 1=m: III. Decay constants in the quenched approximation

Abstract

We report on the computation of the Bs meson decay constant in Heavy Quark Eeffctive Theory on the lattice. The next to leading order corrections in the HQET expansion are included non-perturbatively. We estimate higher order contributions to be very small. The results are extrapolated to the continuum limit, the main systematic error affecting the computation is therefore the quenched approximation used here. The Generalized Eigenvalue Problem and the use of all-to-all propagators are important technical ingredients of our approach that allow to keep statistical and systematic errors under control. We also report on the decay constant fB0's of the first radially excited state in the Bs sector, computed in the static limit.