Exchange effects and large angle proton scattering on light nuclei at intermediate energies: Formalism and application top+Hescattering4

Abstract

The amplitude for elastic scattering of protons on a light nucleus is treated in a manner which takes into account the indistinguishability of the incident and target protons. We propose a simple model in which the direct and knockout amplitudes are represented by an optical potential amplitude. The rest of the exchange amplitude is cast in a form which represents the exchange of a heavy cluster between projectile and target; the heavy particle stripping amplitude. A modified distorted wave Born approximation appropriate for such elastic channel rearrangement is developed. This approximation simplifies the handling of finite range and recoil effects. The calculation of the heavy particle stripping amplitude requires knowledge of the proton-cluster overlap function of the target nucleus. The present model is applied to the scattering of protons on $^{4}\mathrm{He}$ in the energy range 0.1---1.2 GeV. Several overlap functions derived from fits to the charge form factor of $^{4}\mathrm{He}$ are used in the calculations. The general behavior of the large angle cross section is reproduced by our model. Of particular importance is the finding that the results are rather sensitive to the large momentum behavior of the overlap function. Moreover, functions that are derived from the charge form factor after correcting for meson exchange current effects appear to do better at higher energies than those with no correction. Good qualitative agreement with the 180\ifmmode^\circ\else\textdegree\fi{} excitation function is obtained and the calculations predict a second shoulder near 1.1 GeV. We have also investigated the effect of the heavy particle stripping amplitude on the calculation of the large angle polarization.NUCLEAR REACTIONS Large angle $p$ +$^{4}\mathrm{He}$ scattering (${T}_{p}=0.1\ensuremath{-}1.2$ GeV). Exchange effects, heavy particle stripping, modified DWBA. Calculated $\ensuremath{\sigma}(\ensuremath{\theta})$, $P(\ensuremath{\theta})$. Compare different $^{4}\mathrm{He}$ overlap wave functions.