The kaon B-parameter from unquenched mixed action lattice QCD

TL;DR

This paper reports a preliminary lattice QCD calculation of the B_K parameter using a mixed action approach with domain-wall valence quarks and improved staggered sea quarks, demonstrating controlled discretization effects and promising precision.

Contribution

It introduces a mixed action lattice QCD method for calculating B_K with controlled discretization effects and discusses preliminary chiral and continuum extrapolations.

Findings

Discretization effects are under control in the mixed action setup.

Preliminary data for meson masses, decay constants, and B_K are presented.

Good chiral properties of domain-wall quarks enable precise B_K determination.

Abstract

We present a preliminary calculation of B_K using domain-wall valence quarks and 2+1 flavors of improved staggered sea quarks. Both the size of the residual quark mass, which measures the amount of chiral symmetry breaking, and of the mixed meson splitting Delta_mix, a measure of taste-symmetry breaking, show that discretization effects are under control in our mixed action lattice simulations. We show preliminary data for pseudoscalar meson masses, decay constants and B_K. We discuss general issues associated with the chiral extrapolation of lattice data, and, as an example, present a preliminary chiral and continuum extrapolation of f_pi. The quality of our data shows that the good chiral properties of domain-wall quarks, in combination with the light sea quark masses and multiple lattice spacings available with the MILC staggered configurations, will allow for a precise determination of B_K.