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

TL;DR

This paper updates lattice-QCD calculations of form factors for various B-meson semileptonic decays, crucial for CKM matrix element determination and new physics searches, using (2+1+1)-flavor HISQ ensembles with preliminary results.

Contribution

It provides new lattice-QCD form factor calculations for B-meson decays using improved ensembles and systematic error analysis, advancing precision in flavor physics.

Findings

Preliminary form factor results for $f_0$, $f_+$, and $f_T$.

Use of MILC (2+1+1)-flavor HISQ ensembles at multiple lattice spacings.

Studies of systematic uncertainties in lattice calculations.

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.