$B_K$ from improved staggered fermions using SU(3) chiral perturbation theory

Understand

We present recent progress in our calculation of $B_K$ with improved staggered fermions using chiral extrapolations based on SU(3) staggered chiral perturbation theory.

• We have accumulated significantly higher statistics on the coarse, fine, and ultrafine MILC asqtad lattices.
• This leads to a reduction in statistical error and an improved continuum extrapolation.
• Our updated result is $\hat{B}_K = B_K(\text{RGI}) = 0.737 \pm 0.003(\text{stat}) \pm 0.046 (\text{sys})$.