$B_s \to K \ell\nu$ form factors with 2+1 flavors

TL;DR

This paper reports on lattice QCD calculations of $B_s o K \, \ell\nu$ form factors using MILC 2+1 flavor ensembles, aiming to aid in determining the CKM matrix element $|V_{ub}|$ with future experimental data.

Contribution

First calculation of $B_s \to K$ form factors using MILC 2+1 flavor ensembles with multiple lattice spacings and quark masses.

Findings

Form factors $f_0$ and $f_+$ computed for six ensembles.

Results will help determine $|V_{ub}|$ when combined with experimental data.

Lattice spacings range from 0.12 to 0.06 fm.

Abstract

Using the MILC 2+1 flavor asqtad quark action ensembles, we are calculating the form factors $f_0$ and $f_+$ for the semileptonic $B_s \rightarrow K \ell\nu$ decay. A total of six ensembles with lattice spacing from $\approx0.12$ to 0.06 fm are being used. At the coarsest and finest lattice spacings, the light quark mass $m'_l$ is one-tenth the strange quark mass $m'_s$. At the intermediate lattice spacing, the ratio $m'_l/m'_s$ ranges from 0.05 to 0.2. The valence $b$ quark is treated using the Sheikholeslami-Wohlert Wilson-clover action with the Fermilab interpretation. The other valence quarks use the asqtad action. When combined with (future) measurements from the LHCb and Belle II experiments, these calculations will provide an alternate determination of the CKM matrix element $|V_{ub}|$.