Lattice calculation of the kaon-matrix-elementBparameter

We have calculated the kaon-matrix-element B parameter (${\mathrm{B}}_{\mathrm{K}}$) using lattice QCD in the quenched approximation with staggered fermions. We find the correct chiral behavior. Errors from all sources except quenching are under control. At a lattice scale of 2 GeV our result is ${\mathrm{B}}_{\mathrm{K}}$=0.70±0.01(statistical)±0.03(systematic). This translates to a renormalization-group-invariant value B${\mathrm{^}}_{\mathrm{K}}$=0.9–1.0. .AE