Elastic proton scattering from ⁴He at 297 MeV

Differential cross sections, analyzing powers, and spin rotation parameters for elastic scattering of protons on ⁴He at 297 MeV have been measured over a wide angular range (12°≤θ_lab≤66°). Experimental data have been microscopically analyzed with relativistic impulse approximation calculations. The spin observables up to medium scattering angles (θ_c.m.≤40°) are predominantly sensitive to the ratio of the volume integral of scalar density to vector density. With a ratio of 0.92, which is significantly smaller than those for heavier nuclei (0.96-0.98), both spin observables as well as the differential cross section have been quantitatively reproduced. According to nuclear matter calculations, the small ratio reflects a high mass density. At backward angles, the experimental cross sections are larger than any of the values calculated with realistic density distributions.