Extracting γ from Bd0(t)→D(*)+D(*)- and Bd0→Ds(*)+D(*)- decays

We show that the CP phase γ can be obtained from measurements of Bd0(t)→D(*)+D(*)- and Bd0→Ds(*)+D(*)-. These decays are related by flavor SU(3) in the limit where spectator-quark contributions are small. If the pseudoscalar-pseudoscalar decays Bd0(t)→D+D- and Bd0→Ds+D- are used, the leading-order SU(3)-breaking effect is fDs/fD. The dependence on decay constants can be removed by using a double ratio involving two helicity states of the vector-vector decays Bd0→D*+D*- and Bd0→Ds*+D*-. In this case the theoretical error arising from all sources is in the range 5-10%