A Simplified Approach to Determine α\alpha and the Penguin Amplitude in Bd→ππB_{d}\to \pi\pi

The effect of inelastic final-state interactions (IFSI's) on the determination of the weak phase $\alpha$ from the isospin triangles of $B\rightarrow \pi\pi$ is qualitatively illustrated. Neglecting the electroweak penguins and IFSI's and assuming the dominance of the top-quark loop in strong penguin diagrams, we propose an experimentally accessible way to approximately determine $\alpha$ and the penguin amplitude in $B_{d}\rightarrow \pi\pi$. This approach relies on a simplified isospin consideration and the factorization approximation, and its feasibility is irrelevant to the time-dependent measurements of $B_d\rightarrow \pi\pi$.Comment: This work has been accepted for publication in Phys. Lett. B. In the revised version, we add a new section to give a qualitative illustration of the effect of inelastic final-state interactions on the determination of the weak phase $\alpha$ from the isospin triangles of $B\to \pi\pi$ . 10 Latex pages (with 1 figure