Estimate of B(K -> pi nu nubar) from Standard Model fits to lambda_t

We estimate B(K -> pi nu nubar) in the context of the Standard Model by fitting for lambda_t = Vtd x V*ts of the `kaon unitarity triangle' relation. We fit data from epsilon_K, the CP-violating parameter describing K-mixing, and a_{psi K}, the CP-violating asymmetry in B -> J/psi K decays. Our estimate is independent of the CKM matrix element Vcb and of the ratio of Bs to Bd mixing frequencies. The measured value of B(K+ -> pi+ nu nubar) can be compared both to this estimate and to predictions made from the ratio of B mixing frequencies.