Recent progress in calculation of BK using staggered fermions

Abstract

We report on recent progress in the calculation of BK using HYP-smeared improved staggered fermions on the MILC asqtad lattices. We have added measurements on fine (a - 0:09 fm) and superfine (a - 0:06 fm) ensembles at different values of the light sea quark mass (am), as well as increased the statistics on some other ensembles. We find that the results on the fine lattices show a significantly stronger am dependence than those on the superfine and coarse (a - 0:12 fm) lattices. We discuss different methods for accounting for these new results when doing the am and continuum extrapolations.