Tensor polarization of 12C[2+1] in the 16O(13C,12C)17O reaction at 50 MeV

The 16O(13C,12C)17O reaction at 50 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 by analyzing the energy spectrum of 12C[2+1], modulated by the effect of γ ray emission. The deduced t40 values significantly deviate from zero, contrary to the prediction of the distorted-wave Born approximation theory based on one-step p shell neutron stripping without spin-dependent interactions. The phenomenological spin–orbit interaction necessary to reproduce the magnitude of measured t40 is found to be much larger than the folding model prediction. It is shown that the experimental polarization tensors as well as the cross sections can be reproduced by introducing multi-step processes involving excitations in 12C and 13C without introducing spin-dependent interactions.