We present results for the kaon mixing parameter BK obtained using improved staggered fermions on a much enlarged set of MILC asqtad lattices. Compared to our previous publication, which was based largely on a single ensemble at each of the three lattice spacings a≈0.09fm, 0.06fm and 0.045fm, we have added seven new fine and four new superfine ensembles, with a range of values of the light and strange sea-quark masses. We have also increased the number of measurements on one of the original ensembles. This allows us to do controlled extrapolations in the light and strange sea-quark masses, which we do simultaneously with the continuum extrapolation. This reduces the extrapolation error and improves the reliability of our error estimates. Our final result is B^K=0.7379±0.0047(stat)±0.0365(sys).
@article{arxiv.1402.0048,
title = {Improved determination of $B_K$ with staggered quarks},
author = {Taegil Bae and Yong-Chull Jang and Hwancheol Jeong and Chulwoo Jung and Hyung-Jin Kim and Jangho Kim and Jongjeong Kim and Kwangwoo Kim and Sunghee Kim and Weonjong Lee and Jaehoon Leem and Jeonghwan Pak and Sungwoo Park and Stephen R. Sharpe and Boram Yoon},
journal= {arXiv preprint arXiv:1402.0048},
year = {2014}
}