Penguin contributions to B to J/Psi P Decays

The high precision to which the standard model has been confirmed implies that new physics effects have to be small in the observed processes. Together with the outstanding precision expected from present and future collider experiments this renders the evaluation of subleading SM contributions necessary. For the "golden mode", B_d to J/Psi K, these so-called "penguin pollution" terms can be controlled by using flavour symmetry relations. A recent analysis is presented which yields a stronger bound on the maximal penguin influence than previous ones and shows how the corresponding uncertainty can be reduced with coming data.