K -> pi vector form factor with N_f=2+1+1 Twisted Mass fermions

TL;DR

This paper uses lattice QCD with twisted mass fermions to accurately determine the kaon to pion vector form factor, aiding precise extraction of the CKM matrix element |V_{us}| and testing Standard Model unitarity.

Contribution

It provides a new lattice QCD calculation of the K -> pi vector form factor with improved precision using N_f=2+1+1 twisted mass fermions.

Findings

f_+(0)=0.9683(65) for the form factor

|V_{us}|=0.2234(16) from the analysis

Results satisfy Standard Model unitarity constraints

Abstract

We present a lattice QCD determination of the vector form factor of the kaon semileptonic decay K -> pi l nu which is relevant for the extraction of the CKM matrix element |V_{us}| from experimental data. Our result is based on the gauge configurations produced by the European Twisted Mass Collaboration with N_f=2+1+1 dynamical fermions. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our preliminary estimate for the vector form factor at zero momentum transfer is f_+(0)=0.9683(65), where the uncertainty is both statistical and systematic. By combining our result with the experimental value of f_+(0)|V_{us}| we obtain |V_{us}|=0.2234(16), which satisfies the unitarity constraint of the Standard Model at the permille level.