Rare decay B -> K ll form factors from lattice QCD

TL;DR

This paper presents the first unquenched lattice QCD calculation of B -> Kll decay form factors across the full kinematic range, aiding new physics searches.

Contribution

It introduces a novel unquenched lattice QCD approach for B -> Kll form factors, extending previous quenched studies and providing results applicable to the entire q^2 spectrum.

Findings

Form factors valid over full kinematic range

Constructed ratios useful for new physics constraints

Discussed Standard Model observable calculations

Abstract

We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B -> Kll in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks, the highly improved staggered quark formulation for the light valence quarks, and employs the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q^2. We construct the ratios f0/f+ and fT/f+, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables.