Problem of backward proton production

Abstract

The problem of backward proton production in proton-nucleus collisions at intermediate energies is discussed. We develop a model which is based on the correlated two-nucleon-cluster picture. Feynman diagrams including intermediate \ensuremath{\Delta}-resonance states are evaluated. The model is applied first to the deuteron target (p+d\ensuremath{\rightarrow}p+X) at intermediate energies. This presents a good test for the elementary process in our model. Our calculation reproduces well the observed energy spectra of backward protons. Then the model is applied to heavier nuclear targets. There we employ the Fermi momentum distribution which is deduced from other sources of information. This contains high momentum components that play a crucial role in reproducing the high energy part of the backward proton spectra. The model describes remarkably well a wide range of the single particle energy spectra as well as the angular distributions of the backscattered proton. As a further test of the model, we calculate the coincidence spectra of the backward- and the forward-going protons at 800 MeV. The calculation reproduces well the shape (particularly two mountains in the contour plot) of the coincidence experiment which has recently been done by Miake et al. The present analysis strongly supports the existence of the high momentum components in the nuclear Fermi motion. This seems to be rather universal from light to heavy nuclei, and may reflect a new length scale inside the nucleus.