New methods for B meson decay constants and form factors from lattice NRQCD

We determine the normalization of scalar and pseudoscalar current operators made from nonrelativistic b quarks and highly improved staggered light quarks in lattice quantum chromodynamics (QCD) through O(αₛ) and ΛQCD/mb. We use matrix elements of these operators to extract B meson decay constants and form factors, and then compare to those obtained using the standard vector and axial-vector operators. This provides a test of systematic errors in the lattice QCD determination of the B meson decay constants and form factors. We provide a new value for the B and Bₛ meson decay constants from lattice QCD calculations on ensembles that include u, d, s, and c quarks in the sea and those that have the $u/d$ quark mass going down to its physical value. Our results are fB=0.196(6) GeV, f_Bₛ=0.236(7) GeV, and f_Bₛ/fB=1.207(7), agreeing well with earlier results using the temporal axial current. By combining with these previous results, we provide updated values of fB=0.190(4) GeV, f_Bₛ=0.229(5) GeV, and f_Bₛ/fB=1.206(5).