Implications of recent measurements of B meson mixing and ϵ′/ϵK

Within the Standard Model, the recent observation of B_d⁰-B_d⁰ meson mixing provides a lower bound on the top quark mass which is m_t ≳ 50 to 100 GeV, depending on experimental and theoretical uncertainties. Conversely, flavour-conserving neutral-current upper bounds on m_t in combination with B_d⁰-B_d⁰ mixing provide nontrivial lower bounds on hadronic current matrix elements. The lower bound on m_t is only marginally improved by incorporating as a constraint the CP violation ε{lunate}_K observed in the K⁰-K⁰ mass matrix, which allows, in principle, a determination of all the Kobayashi-Maskawa matrix elements. The preliminary measurement of ε{lunate}′/ε{lunate}_K falls comfortably within the range predicted from using these other weak measurements, favouring m_t ∼ 100 GeV within large errors. The Standard Model predicts large. B_s⁰-B_s⁰ mixing, but small CP-violating effects in both B_d⁰-B_s⁰ and B_s⁰-B_s⁰ mixing (≲ 0.3%), whereas nonstandard models can give values as large as 6%. We comment on rate K decays such as K⁺ → π⁺νν in the light of B_d⁰-B_d⁰ mixing. Finally, we review previous phenomenological proposals for the Kobayashi-Maskawa matrix elements and show that they can largely be excluded.