Large Penguin effects in the CP Asymmetry of B0d ->pi+pi-

Abstract

Penguin effects in the CP asymmetries of $B_d^0\to {\pi }^{+}{\pi }^{-}$ , $\text{bd}\to {\rho }^{\pm }{\pi }^{\mp }$ and $\text{bd}\to a_1^{\pm }{\pi }^{\mp }$ are studied as function of the CKM unitarity triangle $\alpha$. Despite a fairly small penguin amplitude, it leads to quite sizable uncertainties in the determination of $\sin (2\alpha )$ from all but very large asymmetries. This effect is maximal for vanishing final state interaction phases, for which it can cause, for instance, an asymmetry of 40\%\ if $\alpha =\pi /2$.

Comments: (14 pages, PHYZZX, 1 figure, available upon request), SLAC-PUB-5911