Spin correlation coefficient for proton-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts/><mml:none/><mml:mn>3</mml:mn></mml:mmultiscripts></mml:math> elastic scattering at 100 MeV

We present the measured spin correlation coefficient ${C}_{y,y}$ for $p\text{\ensuremath{-}}^{3}\mathrm{He}$ elastic scattering at 100 MeV at the angles ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=46.{9}^{\ensuremath{\circ}}$--$149.{2}^{\ensuremath{\circ}}$ in the center-of-mass system. The ${C}_{y,y}$ data and the existing cross section data are compared with rigorous four-nucleon scattering calculations based on realistic nucleon-nucleon potentials. Large differences are seen in the regime around the cross section minimum for both observables. The $\mathrm{\ensuremath{\Delta}}$-isobar effects estimated by the $NN+N\mathrm{\ensuremath{\Delta}}$ coupled-channels approach are small for the cross section. Meanwhile, in ${C}_{y,y}$, the $\mathrm{\ensuremath{\Delta}}$-isobar effects improve the agreement with the data. The analysis of the $p\text{\ensuremath{-}}^{3}\mathrm{He}$ elastic scattering amplitudes implies the necessity of three-nucleon forces ($3N\text{Fs}$) that enhance the vector components in the amplitudes. The obtained results indicate that the spin correlation coefficient ${C}_{y,y}$ expands the knowledge of the nuclear interactions with the $\mathrm{\ensuremath{\Delta}}$ isobar or those including $3N\text{Fs}$ that are masked in nucleon-deuteron elastic scattering.