Seminarium Kosmologia i Fizyka Cząstek

The time-dependent CP asymmetry in Bd → J/ΨKs is the key quantity to determine the angle β of the unitarity triangle. The decay amplitude involves a penguin diagram with an up-quark loop, which obscures the relation between the measured CP asymmetry and β. While this "penguin pollution"was considered smaller than the experimental error of the measurements at past B factories, it matters for the precision a LHCb and Belle II. I present new calculations of the penguin pollution in Bd and Bs decays to charmonium, discussing also Bs → J/Ψ φ which is studied at LHCb to