B0 — ?0 mixing with quenched lattice NRQCD

We present our recent results for the B-parameters, which parameterize the ΔB=2 transition amplitudes. Calculations are made in quenched QCD at β=5.7, 5.9, and 6.1, using NRQCD for heavy quark and the O(a)-improved action for light quark. The operators are perturbatively renormalized including corrections of O(αs/amQ). We examine scaling behavior of the B-parameters in detail, and discuss the systematic uncertainties using scatter of results with different analysis procedures adopted. As a result, we find BBd(mb) = 0.84(2)(8), BBs/BBd = 1.017(10)(+4−0) and BSs(mb)= 0.87(1)(9)(+1−0) in the quenched approximation.