Z penguins and rare B decays

Abstract

Rare B decays of the type $b \to s~\ell^+\ell^-(\nu\bar\nu)$ are analyzed in a generic scenario where New Physics effects enter predominantly via $Z$ penguin contributions. We show that this possibility is both phenomenologically allowed and well motivated on theoretical grounds. The important role played in this context by the lepton forward-backward asymmetry in $B\to K^*\ell^+\ell^-$ is emphasized.