  Factorization based on the soft-collinear effective theory (SCET) can be used
to reduce the number of hadronic parameters in an isospin analysis of B-> pi pi
decays by one. This gives a theoretically precise method for determining the CP
violating phase gamma by fitting to the B-> pi pi data without C_{pi0 pi0}.
SCET predicts that gamma lies close to the isospin bounds. With the current
world averages we find gamma=75^o \pm 2^o {}^{+9^o}_{-13^o}, where the
uncertainties are theoretical, then experimental.
