$B\to \pi \pi$ 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 $\mathrm{\Delta }I=1\mathrm{/}2$ and $\mathrm{\Delta }I=3\mathrm{/}2$ tree amplitudes.