Decay constants $f_B$ and $f_{B_s}$ from HISQ simulations

Fermilab Lattice, MILC Collaborations, :, A. Bazavov, C. Bernard, C. Bouchard, N. Brown, C. DeTar, D. Du, A. X. El-Khadra, E. D. Freeland, E. Gámiz, Steven Gottlieb, U. M. Heller, J. Komijani, A. S. Kronfeld, J. Laiho, L. Levkova, P. B. Mackenzie, C. Monahan, T. Primer, Heechang Na, E. T. Neil, J. N. Simone, R. L. Sugar, D. Toussaint, R. S. Van de Water, R. Zhou

Published 2015-11-07Version 1

We give a progress report on a project aimed at a high-precision calculation of the decay constants $f_B$ and $f_{B_s}$ 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 $f_{B_s}$, respectively.