Proton-3He elastic scattering at low energies

We present new accurate measurements of the differential cross section sigma(theta) and the proton analyzing power A(y) for proton-He-3 elastic scattering at various energies. A supersonic gas-jet target has been employed to obtain these low-energy cross-section measurements. The sigma(theta) distributions have been measured at E-p=0.99, 1.59, 2.24, 3.11, and 4.02 MeV. Full angular distributions of A(y) have been measured at E-p=1.60, 2.25, 3.13, and 4.05 MeV. This set of high-precision data is compared to four-body variational calculations employing realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the unpolarized cross section, the agreement between the theoretical calculation and data is good when a 3N potential is used. The comparison between the calculated and measured proton analyzing powers reveals discrepancies of approximately 50% at the maximum of each distribution. This is analogous to the existing A(y) puzzle known for the past 20 years in nucleon-deuteron elastic scattering.