The kaon semileptonic form factor with near physical domain wall quarks

TL;DR

This paper calculates the K->pi semileptonic form factor using domain wall lattice QCD with near-physical quark masses, providing a precise determination that supports CKM unitarity.

Contribution

It introduces a new lattice QCD calculation of the form factor at zero momentum transfer with near-physical quark masses and multiple lattice spacings, reducing systematic uncertainties.

Findings

Predicted f+(0)=0.9670 with combined errors

Extracted |Vus|=0.2237 supporting CKM unitarity

Achieved sub per mille level confirmation of Standard Model

Abstract

We present a new calculation of the K->pi semileptonic form factor at zero momentum transfer in domain wall lattice QCD with Nf=2+1 dynamical quark flavours. By using partially twisted boundary conditions we simulate directly at the phenomenologically relevant point of zero momentum transfer. We perform a joint analysis for all available ensembles which include three different lattice spacings (a=0.09-0.14fm), large physical volumes (m_pi*L>3.9) and pion masses as low as 171 MeV. The comprehensive set of simulation points allows for a detailed study of systematic effects leading to the prediction f+(0)=0.9670(20)(+18/-46), where the first error is statistical and the second error systematic. The result allows us to extract the CKM-matrix element |Vus|=0.2237(+13/-8) and confirm first-row CKM-unitarity in the Standard Model at the sub per mille level.