Resonant Backward-Angle Heavy-Ion Elastic Scattering

Abstract

We observe strong structure in the excitation functions of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ backward-angle scattering. Angular distributions at the peaks of the elastic excitation function are of the form ${P_J}^2\left(cos\theta \right)$ [approximately $J=15\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=23.3\mathrm{}$ MeV), $J=18\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=26.0\mathrm{}$ MeV), and $J=18\mathrm{}$ ($E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=30.2\mathrm{}$ MeV)]. These results appear to be inconsistent with existing theoretical descriptions of anomalous backward-angle heavy-ion elastic scattering in this mass region.