isospin-violating New Physics

The 2.5σ discrepancy between theory and experiment observed in the difference ACP(B − → πK)−ACP(B̄ → π+K−) can be explained by a new electroweak penguin amplitude. Motivated by this result, we analyse the purely isospinviolating decays B̄s → φρ0 and B̄s → φπ0, which are dominated by electroweak penguins, and show that in presence of a new electroweak penguin amplitude their branching ratio can be enhanced by up to 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. We perform both a model-independent analysis and a study within realistic New Physics models such as a modified-Z0penguin scenario, a model with an additional Z ′ boson and the MSSM. In the latter cases the new amplitude can be correlated with other flavour phenomena, such as semileptonic B decays andBs-B̄s mixing, which impose stringent constraints on the enhancement of the two Bs decays. In particular we find that, contrary to claims in the literature, electroweak penguins in the MSSM can reduce the discrepancy in the B → πK modes only marginally. As byproducts we update the SM predictions to Br(B̄s → φπ0) = 1.6 −0.3 · 10−7 and Br(B̄s → φρ0) = 4.4 −0.7 · 10−7 and perform a state-of-the-art analysis of B → πK amplitudes in QCD factorisation. ∗Alexander-von-Humboldt Fellow