Phenomenology of nonstandard Z couplings in exclusive semileptonic [Formula Presented] transitions

Abstract

The rare decays (Formula presented) (Formula presented) and (Formula presented) are analyzed in a generic scenario where new physics effects enter predominantly via Z penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the (Formula presented) vertex is particularly susceptible to nonstandard dynamics. In addition, such a framework is also interesting phenomenologically since the (Formula presented) coupling is rather poorly constrained by present data. The characteristic features of this scenario for the relevant decay rates and distributions are investigated. We emphasize that both sign and magnitude of the forward-backward asymmetry of the decay leptons in (Formula presented) (Formula presented) carry sensitive information on new physics. The observable (Formula presented) is proposed as a useful probe of nonstandard (Formula presented) violation in (Formula presented) couplings. © 2000 The American Physical Society.