Study of the decay $\bar B ^0 \to D^ *+ \omega \pi^ - $

We report on a study of the decay B0bar -> D*+ omega pi- with the BABAR detector at the PEP-II B-factory at the Stanford Linear Accelerator Center. Based on a sample of 232 million BBbar decays, we measure the branching fraction BF(B0bar -> D*+ omega pi-) = (2.88 +/- 0.21(stat.) +/- 0.31(syst.)) \times 10^{-3}. We study the invariant mass spectrum of the omega pi- system in this decay. This spectrum is in good agreement with expectations based on factorization and the measured spectrum in tau- -> omega pi- nu_tau. We also measure the polarization of the D*+ as a function of the omega pi- mass. In the mass region 1.1 to 1.9 GeV we measure the fraction of longitudinal polarization of the D*+ to be Gamma_L/Gamma = 0.654 +/- 0.042(stat.) +/- 0.016(syst.). This is in agreement with the expectations from heavy-quark effective theory and factorization assuming that the decay proceeds as B0bar -> D*+ rho(1450), rho(1450) -> omega pi-.