Measurement of the weak phase alpha from B0 --> a_1(1260)+- pi-+ decays

We present the measurement, performed by the BABAR Collaboration, of the weak phase alpha from the time dependent CP asymmetries in B0–> a_1(1260)± pi-+ decays. The model error induced by penguin contributions to the B0 --> a_1(1260)± pi-+ channel is estimated from an SU(3) analysis of the branching fractions of B–> a_1(1260) K, B–> K_1(1270) pi, and B–> K_1(1400) pi decays.