Form factors for semileptonic $B\to\pi$, $B_s\to K$ and $B_s\to D_s$ decays

TL;DR

This paper computes semileptonic form factors for B and Bs meson decays using lattice QCD with multiple lattice spacings, providing insights into lepton-flavor universality tests and proposing improved ratios.

Contribution

It presents new lattice QCD calculations of B and Bs semileptonic form factors across three lattice spacings, including improved ratios for lepton-flavor universality tests.

Findings

Form factors for B→π, Bs→K, Bs→Ds decays determined.

Analysis of R-ratios for lepton-flavor universality.

Use of relativistic heavy quark and M"obius domain-wall fermion actions.

Abstract

We report on our determinations of $B\to \pi\ell\nu$, $B_s\to K \ell \nu$ and $B_s\to D_s \ell \nu$ semileptonic form factors. In addition we discuss the determination of $R$-ratios testing lepton-flavor universality and suggest an improved ratio. Our calculations are based on the set of 2+1 flavor domain-wall Iwasaki gauge field configurations generated by the RBC/UKQCD collaboration with three lattice spacings of $1/a = 1.78$, $2.38$, and $2.79\,\text{GeV}$. We use the relativistic heavy quark action for $b$ quarks and charm quarks are simulated with the M\"obius domain-wall fermion action.