Extracting the CKM phase angle γ(≡ φ₃) from isospin analysis in B → Kπ decay

We propose a new method to extract the CKM phase angle γ(≡ φ₃) from the isospin analysis in B → Kπ decays only. Unlike previously proposed methods, we do not employ flavor SU(3) symmetry, so that this method is free from the hadronic uncertainty coming from the SU(3) breaking effect. Neither we adopt any Dalitz-plot analysis, which may involve multiple strong phases and large final state interactions. Since no theoretical assumption, except the isospin relations, is imposed on B → Kπ decays, this method will work well, regardless of possible new physics effects unless the isospin relations do not hold. Since the mixing induced CP asymmetry S _KS π⁰ plays a crucial role in this method, more precise measurement on S_KS π⁰ in future experiments will be greatly helpful to extract γ accurately. Using current experimental data for B → Kπ including S_KS π⁰, we extract γ within 1σ: γ = 71_-13°^+0° or γ = 109_-0°^+57°.