Speaker
Robert Fleischer
(CERN)
Description
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. As the required measurements are not yet available, data for decays with
similar dynamics and the $SU(3)$ flavour symmetry are used to constrain the size of the expected
penguin corrections. Predictions of the CP asymmetries of $B^0_s\to J/\psi K_{\rm S}^0$ and
are given and a scenario is presented to fully exploit the physics potential of this decay, emphasising
also the determination of hadronic parameters and their comparison with theory. In the case
of the benchmark mode $B^0_s\to J/\psi \phi$ used to determine the $B^0_s$--$\bar B^0_s$ mixing
phase $\phi_s$ the penguin effects can be controlled through $B^0_d\to J/\psi \rho^0$ and
$B^0_s\to J/\psi K^*$ decays. The LHCb collaboration has recently presented pioneering
results on this topic. I will discuss their implications and present a roadmap for controlling the
penguin effects.
Author
Robert Fleischer
(CERN)
