  There are at least two methods to calculate $ B_K $ with staggered fermions:
one is the two spin trace formalism and the other is the one spin trace
formalism. We have performed numerical simulations on a $ 16^3 \times 40 $
lattice in full QCD with $ \beta = 5.7 $ and a dynamical quark mass 0.01 in
lattice units. We try various sources to select only the pseudo-Goldstone
bosons and compare the various results.
