Wednesday, February 13, 2013

1302.2644 (R. J. Dowdall et al.)

B-meson decay constants from improved lattice NRQCD and physical u, d, s
and c sea quarks

R. J. Dowdall, C. T. H. Davies, R. R. Horgan, C. J. Monahan, J. Shigemitsu
We present the first lattice QCD calculation of the decay constants f_B and f_{B_s} 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 f_B = 0.186(4) GeV, f_{B_s} = 0.224(5) GeV, f_{B_s}/f_B = 1.205(7) and M_{B_s}-M_B=85(2) MeV, superseding earlier results with NRQCD b quarks. We discuss the implications of our results for the Standard Model rates for B_s -> mu+ mu- and B -> tau nu.
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