Phenomenology of nonstandard Z couplings in exclusive semileptonic b -> s transitions - art. no. 014015

The rare decays B --> K((*))l(+)l(-), B --> K-(*) <<nu>(nu )over bar> and B -s --> mu (+)mu (-) are analyzed in a generic scenario where new physics ef fects enter predominantly via Z penguin contributions. We show that this po ssibility is well motivated on theoretical grounds, as the (s) over bar bZ vertex is particularly susceptible to nonstandard dynamics. In addition, su ch a framework is also interesting phenomenologically since the (s) over ba r bZ coupling is rather poorly constrained by present data. The characteris tic features of this scenario for the relevant decay rates and distribution s are investigated. We emphasize that both sign and magnitude of the forwar d-backward asymmetry of the decay leptons in (B) over bar --> (K) over barl (+)l(-), A(FB)(((B) over bar)), carry sensitive information on new physics. The observable A(FB)(((B) over bar)) + A(FB)((B)) is proposed as a useful probe of nonstandard CP violation in (s) over bar bZ couplings.