In pursuit of new physics with B0 d →J/ψK0 and B0s →J/ψφ decays at the high-precision Frontier

The decays B0d →J/ψK0 S and B0s →J/ψφ play a key role for the determination of the B0q -B0q (q = d, s) mixing phases φd and φs, respectively. The theoretical precision of the extraction of these quantities is limited by doubly Cabibbo-suppressed penguin topologies, which can be included through control channels by means of the SU(3) flavour symmetry of strong interactions. Using the currently available data and a new simultaneous analysis, we discuss the state-of-the-art picture of these effects and include them in the extracted φq values. We have a critical look at the standard model predictions of these phases and explore the room left for new physics. Considering future scenarios for the high-precision era of flavour physics, we illustrate that we may obtain signals for physics beyond the standard model with a significance well above five standard deviations.We also determine effective colour-suppression factors of B0d →J/ψK0, B0s →J/ψK0 S and B0d →J/ψπ0 decays, which serve as benchmarks for QCD calculations of the underlying decay dynamics, and present a new method using information from semileptonic B0d →π-ℓ+νϵ and B0s →K-ℓ+νϵ decays.