Helicity conservation and factorization-suppressed charmlessBdecays

Toward the goal of extracting the weak angle $\alpha ,$ the decay $B^0/B^0\to a_0^{\pm }{\pi }^{\mp }$ was recently measured. The decay $B^0\to a^{+}{\pi }^{-}$ is not only forbidden in the factorization limit of the tree interaction, but also strongly suppressed for the penguin interaction if short-distance QCD dominates. This makes the extraction of $\alpha$ very difficult from $a_0^{\pm }{\pi }^{\mp }.$ We examine similar factorization-suppressed decays, in particular $B^0\to b_1^{+}{\pi }^{-}.$ The prospect of obtaining $\alpha$ is even less promising with $b_1^{\pm }{\pi }^{\mp }.$ To probe how well the short-distance dominance works, we emphasize the importance of testing helicity conservation in the charmless B decays with spins.