Lattice measurement of BBs with a chiral light quark action

Bs − Bs mixing is highly important in testing the Standard Model (SM) and constrains strongly its extensions by bounding the unitarity triangle. Since it is a flavor changing neutral process it occurs through loops so that the corresponding mixing amplitude is a sensitive measure of |Vts| and |Vtb|, as the major SM loop contribution comes from t-quark. The mixing of weak interaction eigenstates Bs and Bs induces a mass gap ∆Ms between the mass eigenstates BsH and BsL. Experimentally, D0 has bounded ∆Ms as 17 ps −1 < ∆Ms < 21 ps −1 (90% CL) [1] and the measurement made at CDF gave ∆Ms = 17.330 +0.426 −0.221 [2]. Theoretically the Bs −Bs mixing is described by means of an Operator Product Expansion, i.e. the Standard Model Lagrangian LSM is reduced to an effective Hamiltonian H∆B=2 eff , up to negligible terms of O(1/M2 W ):