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

TL;DR

This paper reports on progress towards high-precision lattice QCD calculations of the decay constants $f_B$ and $f_{B_s}$ using HISQ simulations, aiming for uncertainties below 2.2 MeV and 1.5 MeV.

Contribution

The study introduces a comprehensive set of HISQ lattice simulations across multiple lattice spacings and quark masses to improve the precision of decay constant calculations.

Findings

Projected uncertainties of 2.2 MeV for $f_B$ and 1.5 MeV for $f_{B_s}$.

Excellent control over continuum limit and discretization errors.

Progress in high-precision decay constant determination.

Abstract

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.