B0 -> D*- a1+: Chirality tests and resolving an ambiguity in   2\beta+\gamma
  We point out that the decays of B mesons into a vector meson and an axial-vector meson can distinguish between left and right-handed polarized mesons, in contrast to decays into two vector mesons. Measurements in B0 -> D*-a1+ are proposed for testing factorization and the V-A structure of the weak b -> c current, and for resolving a discrete ambiguity in 2\beta + \gamma. 
Michael Gronau, Dan Pirjol and Daniel Wyler