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

Abstract

Penguin effects in the CP asymmetries of $B^0_d\rightarrow π^+π^-$ , $\bd\rightarrowρ^{\pm}π^{\mp}$ and $\bd\rightarrow a^{\pm}_1 π^{\mp}$ are studied as function of the CKM unitarity triangle $α$. Despite a fairly small penguin amplitude, it leads to quite sizable uncertainties in the determination of $\sin(2α)$ 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 $α=π/2$.