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

TL;DR

This paper reports the first lattice QCD calculation of B-meson decay constants using physical u, d, s, and c sea quarks, employing improved NRQCD for b quarks, resulting in precise values relevant for Standard Model predictions.

Contribution

It provides the first calculation of B-meson decay constants with physical light quark masses using improved lattice techniques and includes effects of all four sea quark flavors.

Findings

Calculated decay constants: f_B=0.186(4) GeV, f_{B_s}=0.224(5) GeV

Determined the ratio f_{B_s}/f_B=1.205(7)

Measured the B_s - B mass difference as 85(2) MeV

Abstract

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.