(p, 2p) Reactions at 600 MeV on Deuterium and Helium-4

The differential cross section ($\frac{d\sigma }{\mathrm{dEd}{\Omega }^2}$) for ($p, 2p$) reactions induced by 600-MeV protons on deuterium and helium-4 has been studied for symmetric reaction kinematics. By varying the detection angles of the two outgoing protons, we investigated the $\mathrm{D}(p, 2p)n$ reaction for recoil momenta of the residual nucleus between 180 MeV/c antiparallel and 370 MeV/c parallel to the incident proton direction, respectively. For the ${\mathrm{He}}^4(p, 2p){\mathrm{H}}^3$ reaction, the corresponding numbers are 148 and 298 MeV/c, respectively. Some data for asymmetric reactions in helium-4 are also presented. Analyzing the data in terms of the plane-wave-impulse approximation, we calculate the single-proton momentum distribution in both nuclei. For deuterium, we observe a sudden change of slope in the momentum distribution around 150 MeV/c, which cannot be explained with theoretical momentum distributions obtained by Fourier transforming Hulthén or Hamada-Johnston deuteron wave functions. In helium-4, the momentum distribution is nearly Gaussian up to about 180 MeV/c; above this value, an excess of large momentum components is observed. Both the deuterium and helium-4 results seem to indicate that the plane-wave impulse approximation is not valid at this energy and for the reaction parameters investigated here. Multiple scattering effects might be at the origin of the apparent excess of large Fermi momentum components obtained when the data are analyzed with the impulse approximation.