Phenomenology of non - standard Z couplings in exclusive semileptonic b ! s transitions 1

The rare decays B ! K `` , B ! K )  and Bs ! + are analyzed in a generic scenario where New Physics e ects enter predominantly via Z penguin contributions. We show that this possibility is well motivated on theoretical grounds, as the sbZ vertex is particularly susceptible to non-standard dynamics. In addition, such a framework is also interesting phenomenologically since the sbZ 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 B ! K `` , A B) FB , carry sensitive information on New Physics. The observable A B) FB + A FB is proposed as a useful probe of non-standard CP violation in sbZ couplings. Work supported by the Department of Energy, Contract DE-AC03-76SF00515