The Bs width difference beyond the Standard Model

The Standard Model predicts a large width difference in the Bs system. New physics can contribute significantly to the mass difference. If this contribution is CP violating, this will always result in a reduction of the width difference. The analyses of measurements of the width difference using Bs decays into CP eigenstates have to be modified in the presence of new physics. We discuss how the width difference and the new CP violating phase in Bs mixing can be measured.