A Precision Method for Determining γ from B→ππ Decays

Factorization based on the soft-collinear effective theory reduces the number of hadronic parameters in an isospin analysis of B→ππ decays by one. Using the available B→ππ data allows us to simultaneously fit for these hadronic parameters and obtain a precise value of the CP violating phase γ, namely γ=74−16−9∘∘+9+2∘. The first uncertainties are experimental and the second are theoretical and dominated by power corrections to our analysis. The theory error is lopsided because SCET predicts that γ lies close to the upper bound determined by isospin, γ≤75.2±8.2∘ (where the error here is experimental).