Constraints ont-quark mass and quark mixings fromKL→μμ¯, and relations to other rare decays

Incorporating the recent measurements of the branching ratio (${\mathit{K}}_{\mathit{L}}^0$→μμ¯)/(${\mathit{K}}_{\mathit{L}}^0$→all) we have extracted newer constraints on the t-quark mass and the unknown Kobayashi-Maskawa quark-mixing parameters. This is used to estimate the branching ratio of ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$νν¯ in the minimal standard model; it is found to lie in the tighter range of (1–2.5)×${10}^{\mathrm{-}10}$. Effects of a lower branching ratio for ${\mathit{K}}_{\mathit{L}}^0$→μμ¯ have a minimal impact on other rare kaon and B-meson decays.