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

Preprint number: CP3-Origins-2014-11 DNRF90 and DIAS-2014-11
Authors: Fabio Bernardoni (NIC @ DESY), Benoît Blossier (Paris-Sud University), John Bulava (Trinity College), Michele Della Morte (CP3-Origins & DIAS and IFIC and CSIC), Patrick Fritzsch (Humboldt-Universität zu Berlin), Nicolas Garron (Trinity College), Antoine Gérardin (Paris-Sud University), Jochen Heitger (Universität Münster), Hubert Simma (NIC @ DESY), Rainer Sommer (NIC @ DESY), and Georg von Hippel (University of Mainz)
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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=2 gauge field ensembles, covering three lattice spacings a (0.08-0.05)fm and pion masses down to 190MeV, 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)MeV, fBs=224(14)MeV and 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.