Semileptonic $B\to\pi\ell\nu$, $B\to D\ell\nu$, $B_s\to K\ell\nu$, and $B_s\to D_s\ell\nu$ decays

TL;DR

This paper updates lattice QCD calculations of semileptonic B and Bs decay form factors using RBC-UKQCD ensembles, aiming to improve predictions of CKM elements and lepton flavor universality tests.

Contribution

It provides new nonperturbative lattice QCD results for semileptonic decay form factors across the full kinematic range, utilizing multiple lattice spacings and advanced analysis techniques.

Findings

Form factors over full $q^2$ range obtained

Predictions for CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$

Support for lepton flavor universality tests

Abstract

We present updates for our nonperturbative lattice QCD calculations to determine semileptonic form factors for exclusive $B\to \pi\ell\nu$, $B\to D \ell\nu$, $B_s\to K\ell \nu$, and $B_s\to D_s\ell\nu$ decays. Our calculation is based on RBC-UKQCD's set of $2+1$-dynamical-flavor gauge field ensembles. In the valence sector we use domain wall fermions for up/down, strange and charm quarks, whereas bottom quarks are simulated with the relativistic heavy quark action. The continuum limit is based on three lattice spacings. Using kinematical $z$ expansions we aim to obtain form factors over the full $q^2$ range. These form factors are the basis for predicting ratios addressing lepton flavor universality or, when combined with experimental results, to obtain CKM matrix elements $|V_{ub}|$ and $|V_{cb}|$.