Numerical Study of $ K^0$--$\bar{K}^0$ Mixing and $ B_K $
  We have computed $ B_K $ with staggered fermions, using two different methods: both in the one spin trace form and two spin trace form. Renormalized results in both forms are in good agreement. The numerical simulations were performed on a $ 16^3 \times 40 $ lattice in full QCD with $ \beta = 5.7 $. We also tried an improved wall source method in order to select only the pseudo-Goldstone bosons and compare the numerical results obtained with those from the conventional wall source method. We have studied $ B_K $ with a series of non-degenerate quark anti-quark pairs and saw no effect on $ B_K $, although dramatic effects in the chiral limit were seen on the individual terms making up $ B_K $. 
Weonjong Lee (IBM T.J. Watson Research Center) and Markus Klomfass