In pursuit of new physics with Bs decays

Abstract

The presence of a sizable CP-violating phase in Bs-B̄s mixing would be an unambiguous signal of physics beyond the standard model. We analyze various possibilities to detect such a new phase considering both tagged and untagged decays. The effects of a sizable width difference ΔΓ between the Bs mass eigenstates, on which the untagged analyses rely, are included in all formulas. A novel method to find this phase from simple measurements of lifetimes and branching ratios in untagged decays is proposed. This method does not involve two-exponential fits, which require much larger statistics. For the tagged decays, an outstanding role is played by the observables of the time-dependent angular distribution of the Bs→J/ψ[→l+l-]φ[→K +K-] decay products. We list the formulas needed for the angular analysis in the presence of both a new CP-violating phase and a sizable ΔΓ, and propose methods to remove a remaining discrete ambiguity in the new phase. This phase can therefore be determined in an unambiguous way. © 2001 The American Physical Society.