mixing, lifetime difference ΔΓs and the Physics Beyond Standard Model

The analysis of tagged Bs→J/ψϕ decays determines the CP phase in mixing with a two–fold ambiguity. The solutions differ in the sign of which equals the sign of the width difference ΔΓs among the two Bs mass eigenstates. In this talk, I discuss the removal of this sign ambiguity with the help of Bs→DsK decays. In addition, I discuss the new physics models that contribute to the absorptive part of mixing through the decay b→sτ+τ− which may enhance ΔΓs all the way up to its current experimental bound. It can also help to understand the recent data on anomalous like-sign dimuon charge asymmetry observed by DØ. A measurement of BR(Bs→τ+τ−) is thus crucial for a better understanding of new physics involved in mixing.