B to π π decays: branching ratios and CP asymmetries

Theoretically motivated smallness of the penguin amplitude in $B \to \pi \pi$ decays allowes to calculate the value of the unitarity triangle angle $\alpha (\phi_2)$ with good accuracy. The relatively large branching ratio of the decay into $\pi^0 \pi^0$ is explained by the large value of FSI phase difference between $\Delta I = 1/2$ and $\Delta I = 3/2$ tree amplitudes.