Decay constants of B-mesons from non-perturbative HQET with two light dynamical quarks

We present a computation of B-meson decay constants from lattice QCD simulations within the framework of Heavy Quark Effective Theory for the b-quark. The next-to-leading order corrections in the HQET expansion are included non-perturbatively. Based on Nf=2Nf=2 gauge field ensembles, covering three lattice spacings a≈(0.08–0.05) fma≈(0.08–0.05) fm and pion masses down to 190 MeV190 MeV, a variational method for extracting hadronic matrix elements is used to keep systematic errors under control. In addition we perform a careful autocorrelation analysis in the extrapolation to the continuum and to the physical pion mass limits. Our final results read fB=186(13) MeVfB=186(13) MeV, fBs=224(14) MeVfBs=224(14) MeV and fBs/fB=1.203(65)fBs/fB=1.203(65). A comparison with other results in the literature does not reveal a dependence on the number of dynamical quarks, and effects from truncating HQET appear to be negligible.