Determining weak phase γ and probing new physics in b→s transitions from B→η'K

We present a method of determining the weak phase γ in the Cabibbo-Kobayashi-Maskawa matrix from the decays B→ηK,η'K alone. Given a large ratio between color-suppressed and color-allowed tree diagrams extracted from global ππ(K) fits, γ is determined from the current data of η'K and the result is in agreement with the global standard model (SM) fits. However, a smaller ratio from factorization based calculations gives γ∝90 . New physics beyond the SM can be distinguished if γ obtained in the η'K modes is significantly different from the ones from other modes or other approaches. The effective value of γ from η'K is very sensitive to new physics contributions and can be used to extract new physics parameters for a class of models which do not give contributions to strong phases significantly. (orig.)