The B -> pi l nu semileptonic form factor from three-flavor lattice QCD: A model-independent determination of |V(ub)|

TL;DR

This paper presents a lattice QCD calculation of the B to pi semileptonic form factor, combining lattice and experimental data to determine |V(ub)| with reduced uncertainty in a model-independent way.

Contribution

The study provides a new, model-independent determination of |V(ub)| by combining lattice QCD results with experimental data using a parameterization based on analyticity and unitarity.

Findings

|V(ub)| = 3.38 +/- 0.36 x 10^-3

Reduced uncertainty in |V(ub)| compared to previous methods

First simultaneous lattice and experimental fit for this form factor

Abstract

We calculate the form factor f_+(q^2) for B-meson semileptonic decay in unquenched lattice QCD with 2+1 flavors of light sea quarks. We use Asqtad-improved staggered light quarks and a Fermilab bottom quark on gauge configurations generated by the MILC Collaboration. We simulate with several light quark masses and at two lattice spacings, and extrapolate to the physical quark mass and continuum limit using heavy-light meson staggered chiral perturbation theory. We then fit the lattice result for f_+(q^2) simultaneously with that measured by the BABAR experiment using a parameterization of the form factor shape in q^2 which relies only on analyticity and unitarity in order to determine the CKM matrix element |V(ub)|. This approach reduces the total uncertainty in |V(ub)| by combining the lattice and experimental information in an optimal, model-independent manner. We find a value of |V(ub)| x 10^3 = 3.38 +/- 0.36.