We present the measured data of the proton analyzing power $A_y$ in polarized proton elastic scattering of an unpolarized ${}^3\mathrm{He}$ target and the ${}^3\mathrm{He}$ analyzing power $A_{0y}$ in unpolarized proton scattering of a polarized ${}^3\mathrm{He}$ target at three intermediate energies: 50, approximately 65, and 100 MeV. The experimental results are compared with rigorous four-nucleon scattering calculations based on the realistic charge dependent (CD) Bonn nucleon-nucleon ($NN$) potential. Large discrepancies are observed for both $A_y$ and $A_{0y}$ at the angles where the observables exhibit a minimum and a maximum at almost all three measured energies. The examination for discrepancies has been extended to the lower incident energy of 8.5 MeV, revealing that differences exist from 8.5 to 100 MeV for $A_y$. The $\mathrm{\Delta }$-isobar effects derived using the $NN+N\mathrm{\Delta }$ coupled-channel approach do not account for the $A_y$ and $A_{0y}$ data at the three investigated energies. We therefore estimated the effects of the irreducible three-body forces associated with the CD $\mathrm{Bonn}+\mathrm{\Delta }$-isobar calculations. We also analyzed the $p\text{−}{}^3\mathrm{He}$ elastic scattering amplitudes. The results obtained suggest that $A_y$ and $A_{0y}$ for $p\text{−}{}^3\mathrm{He}$ elastic scattering at intermediate energies are insensitive to the $2\pi$-exchange-type three-nucleon forces ($3N\mathrm{Fs}$), but enhance nuclear interactions, including the $3N\mathrm{Fs}$ masked in nucleon-deuteron elastic scattering.

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• Elastic scattering reactions
• Few-body systems
• H & He induced nuclear reactions
• Nuclear forces
• Nucleon-nucleon interactions
• Polarization phenomena
• A ≤ 5