Decay constants f_B and f_Bs from HISQ simulations

We give a progress report on a project aimed at a high-precision calculation of the decay constants fB and fBs from simulations with HISQ heavy and light valence and sea quarks. Calculations are carried out with several heavy valence-quark masses on ensembles with 2+1+1 flavors of HISQ sea quarks at five lattice spacings and several light sea-quark mass ratios m_ud=m_s, including approximately physical sea-quark masses. This range of parameters provides excellent control of the continuum limit and of heavy-quark discretization errors. We present a preliminary error budget with projected uncertainties of 2.2 MeV and 1.5 MeV for f_B and f_Bs , respectively.,We give a progress report on a project aimed at a high-precision calculation of the decay constants f_B and f_Bs from simulations with HISQ heavy and light valence and sea quarks. Calculations are carried out with several heavy valence-quark masses on ensembles with 2+1+1 flavors of HISQ sea quarks at five lattice spacings and several light sea-quark mass ratios mud=ms, including approximately physical sea-quark masses. This range of parameters provides excellent control of the continuum limit and of heavy-quark discretization errors. We present a preliminary error budget with projected uncertainties of 2.2 MeV and 1.5 MeV for f_B and f_Bs , respectively.