$B$-meson semileptonic form factors on (2+1+1)-flavor HISQ ensembles

Abstract

We report updates to an ongoing lattice-QCD calculation of the form factors for the semileptonic decays $B\to \pi \ell \nu$, $B_s\to K\ell \nu$, $B\to \pi {\ell }^{+}{\ell }^{-}$, and $B\to K{\ell }^{+}{\ell }^{-}$. The tree-level decays $B_{(s)}\to \pi (K)\ell \nu$ enable precise determinations of the CKM matrix element $|V_{ub}|$, while the flavor-changing neutral-current interactions $B\to \pi (K){\ell }^{+}{\ell }^{-}$ are sensitive to contributions from new physics. This work uses MILC's (2+1+1)-flavor HISQ ensembles at approximate lattice spacings between $0.057$ and $0.15$ fm, with physical sea-quark masses on four out of the seven ensembles. The valence sector is comprised of a clover $b$ quark (in the Fermilab interpretation) and HISQ light and $s$ quarks. We present preliminary results for the form factors $f_0$, $f_{+}$, and $f_T$, including studies of systematic errors.

Comments: 7 pages; 3 figures; presented at the 37th International Symposium on Lattice Field Theory, 16-22 June 2019, Wuhan, China