Probing new physics in electroweak penguins through Bd and Bs decays

An enhanced electroweak penguin amplitude due to the presence of unknown new physics can explain the discrepancies found between theory and experiment in the B → πK decays, in particular in ACP(B− → π0K−) − ACP(B̄0 → π+K−), but the current precision of the theoretical and experimental results does not allow to draw a firm conclusion. We argue that the B̄s → ϕρ0 and B̄s → ϕπ0 decays offer an additional tool to investigate this possibility. These purely isospin-violating decays are dominated by electroweak penguins and we show that in presence of a new physics contribution their branching ratio can be enhanced by about an order of magnitude, without violating any constraints from other hadronic B decays. This makes them very interesting modes for LHCb and future B factories. In [1] we have performed both a model-independent analysis and a study within realistic New Physics models such as a modified-Z0-penguin scenario, a model with an additional Z′ boson and the MSSM. In this article we summarise the most important results of our study.