A precise determination of $α$ using $B^0\toρ^+ρ^-$ and $B^+\to K^{*0}ρ^+$

Abstract

The effect of the penguin amplitude on extracting $α$ from CP asymmetries in $B^0\to ρ^+ρ^-$ decays is studied using information on the SU(3)-related penguin amplitude in $B^+\to K^{*0}ρ^+$. Conservative bounds on non-factorizable SU(3) breaking, small amplitudes, and the strong phase difference between tree and penguin amplitudes, are shown to reduce the error in $α$ in comparison with the one obtained using isospin symmetry in $B\toρρ$. Current measurements imply $α= [90 \pm 7 f{\rm exp})^{+2}_{-5} ({\rm th})]^\circ$.