K -> pi l nu form factors with staggered quarks

TL;DR

This paper discusses a lattice QCD calculation of the K to pi semileptonic form factor f_+^{K pi}(0), crucial for determining the CKM matrix element |V_{us}|, using improved staggered quark actions and twisted boundary conditions.

Contribution

It introduces a methodology combining HISQ valence quarks, asqtad sea quarks, and twisted boundary conditions for precise form factor calculations.

Findings

Initial results at different lattice spacings and quark masses.

Use of twisted boundary conditions to access near-zero momentum transfer.

Discussion of correlator fitting techniques.

Abstract

We report on the status of the Fermilab-MILC calculation of the form factor f_+^{K pi}(0), needed to extract the CKM matrix element |V_{us}| from experimental data on K semileptonic decays. The HISQ formulation is used in the simulations for the valence quarks, while the sea quarks are simulated with the asqtad action (MILC N_f=2+1 configurations). We discuss the general methodology of the calculation, including the use of twisted boundary conditions to get values of the momentum transfer close to zero and the different techniques applied for the correlators fits. We present initial results for lattice spacings a=0.12fm and a=0.09fm, and several choices of the light quark masses.