Probing New Physics in B to pi K Decays

Decays of the type B to pi K have received a lot of attention over the last few decades. They are particularly interesting because tree amplitudes are suppressed; the leading contribution comes from QCD penguin topologies. Moreover, electroweak penguin amplitudes contribute at the level of the tree topologies. We perform a state-of-the-art analysis of CP violation in B_d^0 to pi^0 K_S, which reveals a tension with the Standard Model. A modified electroweak penguin sector provides an attractive explanation. We present a new method to determine the relevant parameters, which makes use of an isospin relation and requires only minimal SU(3) input. The mixing-induced CP asymmetry of B_d^0 to pi^0 K_S plays a key role in the analysis. The implementation of our strategy at Belle II and LHCb may establish New Physics and reveal new sources of CP violation in the electroweak penguin sector.