B-meson decay constants from improved lattice NRQCD and physical u, d, s and c sea quarks
Abstract
We present the first lattice QCD calculation of the decay constants fB and fBs with physical light quark masses. We use configurations generated by the MILC collaboration including the effect of u, d, s and c HISQ sea quarks at three lattice spacings and with three u/d quark mass values going down to the physical value. We use improved NRQCD for the valence b quarks. Our results are fB = 0.186(4) GeV, fBs = 0.224(5) GeV, fBs/fB = 1.205(7) and MBs-MB=85(2) MeV, superseding earlier results with NRQCD b quarks. We discuss the implications of our results for the Standard Model rates for Bs -> mu+ mu- and B -> tau nu.
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