G. W. Hoffmann

0.8 GeV p + Pb 208 elastic scattering and the quantity Δ r np

Analyses of 0.8 and 1 GeV p+/sup 208/Pb elastic angular distribution data have obtained neutron-proton root-mean-square radius differences (..delta..r/sub n/p) which are not consistent. Therefore, the 0.8 GeV experiment was repeated using a high resolution spectrometer. The new higher precision data are consistent with the older data, apart from a 15% overall normalization difference. A second order Kerman-McManus-Thaler optical model analysis of the new data, using a model-independent neutron density, yields ..delta..r/sub n/p=0.14 +- 0.04 fm, in good agreement with the most recent result obtained (0.16 +- 0.05 fm) from a similar analysis of the older 0.8 GeV data. In addition, the elastic angular distribution was extended to 42.5/sup 0/ center of mass in order to explore the momentum transfer region from 3.5 to 5.3 fm/sup -1/. Although the familiar diffraction pattern persists to 42.5/sup 0/, it was not possible within the framework of our application of the Kerman-McManus-Thaler optical model to fit the data even qualitatively at the larger momentum transfers.