Role of multi-step processes in 16O(11B,12C)15N at 41.25 MeV

The 16O(11B,12C)15N reaction at 41.25 MeV has been investigated using the kinematical coincidence method. Polarization tensors t20 and t40 of 12C[2+1] for the quantization axis taken along the direction of propagation have been measured at center-of-mass angles (Θc.m.) between 48° and 62° by analyzing the energy spectrum of 12C[2+1] modulated by the effect of γ-ray emission. The cross-sections of the transfer reactions leading to the 12C[g.s.]+15N[g.s.], 12C[2+1]+15N[g.s.] and 12C[g.s.]+15N[3/2-1] final states have also been measured in the range 48°≤Θc.m.≤ 120°. The polarization tensor terms of 12C[2+1] largely deviating from zero have been observed, contrary to the prediction by the distorted-wave Born approximation (DWBA). The one-step DWBA calculation also fails in describing the transfer reaction cross-sections. It is shown that the coupled channel model calculation including excitations and reorientations in 11B and 12C satisfactorily reproduces both the tensor terms and the cross-sections of the transfer reactions. The multi-step processes passing through the excited states of 11B are found to significantly contribute to the reaction.