The search for new physics in $B \to K \ell^+\ell^-$ and $B \to K \nu\bar{\nu}$ using precise lattice QCD form factors

TL;DR

This paper provides improved lattice QCD form factors for B to K decays, enabling more precise Standard Model predictions and analysis of potential new physics signals in rare B decay processes.

Contribution

The authors present highly accurate scalar, vector, and tensor form factors for B to K decays using advanced lattice QCD techniques, covering the full q^2 range with reduced uncertainties.

Findings

Form factors are three times more precise at q^2=0 than previous work.

Comparison with experimental data reveals tensions in rare B decay processes.

Enhanced theoretical inputs improve the sensitivity to new physics in B decays.

Abstract

We present HPQCD's improved scalar, vector and tensor form factors for $B \to K$ semileptonic decays, using the heavy-HISQ formalism for more accurate normalisation of the weak currents. Working with masses close to the physical $b$ on the finest ensemble and including three ensembles with physical light quarks, we cover the full physical $q^2$ range with good precision. Our uncertainties at $q^2=0$ are a factor of three better than earlier work. We compare Standard Model observables using our form factors to experimental measurements for the rare flavour changing neutral current processes $B \to K \ell^+\ell^-$ and $B \to K \nu\bar{\nu}$ and discuss the significance of the tensions that arise.