A Roadmap to Control Penguin Effects in $B^0_d\to J/\psi K_{\rm S}^0$ and $B^0_s\to J/\psi \phi$

Understand

Measurements of CP violation in $B^0_d\to J/\psi K_{\rm S}^0$ and $B^0_s\to J/\psi \phi$ decays play key roles in testing the quark-flavour sector of the Standard Model.

• The theoretical interpretation of the corresponding observables is limited by uncertainties from doubly Cabibbo-suppressed penguin topologies.
• With continuously increasing experimental precision, it is mandatory to get a handle on these contributions, which cannot be calculated reliably in QCD.
• In the case of the measurement of $\sin2\beta$ from $B^0_d\to J/\psi K_{\rm S}^0$, the $U$-spin-related decay $B^0_s\to J/\psi K_{\rm S}^0$ offers a tool to control the penguin effects.