A precise determination of α using B0→ρ+ρ− and B+→K∗0ρ+

The effect of the penguin amplitude on extracting α from CP asymmetries in B0→ρ+ρ− decays is studied using information on the SU(3)-related penguin amplitude in B+→K∗0ρ+. 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→ρρ. Current measurements imply α=[90±7(exp)−5+2(th)]°.