Kaon semileptonic decays near the physical point

TL;DR

This paper reports on lattice QCD calculations of the $K o\pi$ vector form factor near the physical pion mass, aiming to improve the precision of the CKM matrix element $|V_{us}|$ determination.

Contribution

It provides a preliminary lattice QCD computation of the $K o\pi$ form factor using domain wall fermions at near-physical pion masses with reduced systematic errors.

Findings

Form factor computed at near-physical pion mass

Use of twisted boundary conditions to reduce interpolation errors

Preliminary results suggest improved precision in $|V_{us}|$ extraction

Abstract

The CKM matrix element $|V_{us}|$ can be extracted from the experimental measurement of semileptonic $K\to\pi$ decays. The determination depends on theory input for the corresponding vector form factor in QCD. We present a preliminary update on our efforts to compute it in $N_f=2+1$ lattice QCD using domain wall fermions for several lattice spacings and with a lightest pion mass of about $170\,\mathrm{MeV}$. By using partially twisted boundary conditions we avoid systematic errors associated with an interpolation of the form factor in momentum-transfer, while simulated pion masses near the physical point reduce the systematic error due to the chiral extrapolation.