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.
@article{arxiv.0905.3947,
title = {The neutral kaon mixing parameter B_K from unquenched mixed-action lattice QCD},
author = {C. Aubin and Jack Laiho and Ruth S. Van de Water},
journal= {arXiv preprint arXiv:0905.3947},
year = {2010}
}
Comments
72 pages, 26 figures, 6 tables, uses RevTeX. Discussion about chiral/continuum extrapolation expanded for clarification, references added, conclusions remain unchanged, version published in Phys. Rev. D