Extraction of $\alpha$ From the CP Asymmetry in B^0/\bar B^0 --> pi+ pi- Decays

Abstract

The influence of strong and electroweak penguin amplitudes in $B/\bar{B}\to {\pi }^{+}{\pi }^{-}$ is investigated in connection with the determination of the unitarity triangle angle $\alpha$ of the CKM matrix. A relation between the observable asymmetry, the angle $\alpha$, and the penguin amplitude is established. A model calculation of the penguin amplitude shows that the CP asymmetry in $B^0\to {\pi }^{+}{\pi }^{-}$ decays is only mildly influenced by the penguin amplitudes. Experimental limits on pure penguin and penguin dominated processes are consistent with the model. This information also suggests in a rather model independent way that penguin amplitudes will not be a serious complicating factor in the determination of $\alpha$ from the ${\pi }^{+}{\pi }^{-}$ time dependent asymmetry.

Comments: 15 pages, Latex, three figures available upon request