We present a lattice QCD calculation of the hadronic form factors for the semileptonic decays $B \to \pi$ and $B_{(s)} \to D_{(s)} \ell \nu$, computed using the highly improved staggered quark action for both valence and sea quarks on the MILC collaboration’s $2+1+1$-flavor ensembles with lattice spacings ranging from $0.09\,\mathrm{fm}$ to $0.03\,\mathrm{fm}$, many with physical pion masses.
On our finest ensembles, we compute the form factors directly at the physical $b$-quark mass.
We discuss the computational setup and analysis strategies for two- and three-point correlation functions. For $B_{(s)} \to D_{(s)}$, we present preliminary results of chiral-continuum fits for the scalar and vector form factors.
The goal of this project is a percent-level determination of the scalar and vector form factors to enable high-precision determinations of $|V_{ub}|$ and$|V_{cb}|$.
This work fits into a broader program of lattice-QCD studies of weak $B$-meson decays by the MILC and Fermilab Lattice collaborations.