In the Standard Model, B_d⁰- B_d⁰ oscillations occur through a second order process (a box diagram) with a loop containing W and up-type quarks. The box diagram with the top quark gives the dominant contribution. The B_d⁰- B_d⁰ oscillation frequency, which is related to the mass difference between the light and the heavy mass eigenstates of the system is expressed, in the Standard Model, as function of ρ, η and the other elements of CKM matrix

where S(x_t ) is the Inami-Lim function and x_t = m_t²/ M_W². m_t is the MS top mass, m_t^MS (m_t^MS), and η_c is the perturbative QCD short distance NLO correction. The remaining factor encodes the information of non-perturbative QCD. The experimental values we use are summarized in the Table of Inputs.

(EPS) [JPG] Bound on Rt from Δmd Rt = 0.93 ± 0.14 ([0.69,1.25] @ 95% Prob.)

(EPS) [JPG] bound from Δ md on (ρ, η) plane