# 30th International Symposium on Lepton Photon Interactions at High Energies

Jan 10 – 14, 2022
Online only
Europe/London timezone

## Improved $V_{cs}$ determination from $D \to K \ell\nu$ and search for new physics in $B \to K \ell^+\ell^-$ using precise lattice QCD form factors

Jan 12, 2022, 9:20 AM
20m
Online only

#### Online only

Parallel session talk Flavour

### Speaker

Mr William Parrott (University of Glasgow)

### Description

We discuss HPQCD's recent precise determinations of the $D \to K$ and $B \to K$ scalar, vector and tensor form factors from full lattice QCD using the HISQ formalism.
Our $D \to K$ form factors allow us to calculate the differential rate for $D\to K \ell\nu$ with improved precision. Comparison with experimental results gives the CKM element $V_{cs}$ to better than 1\% for the first time: $|V_{cs}|=0.9663(80)$. We also demonstrate that the $q^2$-dependence of the rate predicted from QCD matches that of experiment.
Increasing the heavy quark mass from charm to bottom in our lattice QCD calculation gives access to the form factors for $B \to K \ell^+\ell^-$ across the full $q^2$ range of the decay process. We compare Standard Model observables calculated from our form factors to experimental measurements to pin down new physics contributions with improved significance over previous results.

### Primary author

Mr William Parrott (University of Glasgow)