The neutral kaon mixing parameter B_K from unquenched mixed-action lattice QCD

TL;DR

This paper presents a precise calculation of the neutral kaon mixing parameter B_K using unquenched mixed-action lattice QCD with improved staggered sea quarks and domain-wall valence quarks, reducing systematic uncertainties.

Contribution

It introduces a mixed-action lattice QCD approach to accurately determine B_K, controlling systematic errors and extrapolating to physical quark masses and continuum limit.

Findings

B_K^{MSbar, NDR}(2 GeV) = 0.527(6)(20)

Controlled systematic uncertainties in lattice calculation

First precise unquenched mixed-action B_K determination

Abstract

We calculate the neutral kaon mixing parameter B_K in unquenched lattice QCD using asqtad-improved staggered sea quarks and domain-wall valence quarks. We use the "2+1" flavor gauge configurations generated by the MILC Collaboration, and simulate with multiple valence and sea quark masses at two lattice spacings of a ~ 0.12 fm and a ~ 0.09 fm. We match the lattice determination of B_K to the continuum value using the nonperturbative method of Rome-Southampton, and extrapolate B_K to the continuum and physical quark masses using mixed action chiral perturbation theory. The "mixed-action" method enables us to control all sources of systematic uncertainty and therefore to precisely determine B_K; we find a value of B_K^{MSbar, NDR}(2 GeV) = 0.527(6)(20), where the first error is statistical and the second is systematic.