Quantitative description of the $^{20}$Ne($p$,$p\alpha$)$^{16}$O cross section as a means of probing the surface $\alpha$ amplitude
The proton-induced $\alpha$ knockout reaction has been utilized for decades to investigate the $\alpha$ cluster states of nuclei, of the ground state in particular. However, even in recent years, it is reported that the deduced $\alpha$ spectroscopic factors from $\alpha$ knockout experiments and reaction analyses with a phenomenological $\alpha$ cluster wave function diverge depending on the kinematical condition of the reaction. In the present study we examine the theoretical description of the $^{20}$Ne($p$,$p\alpha$)$^{16}$O cross section based on the antisymmetrized molecular dynamics and the distorted wave impulse approximation by comparing with existing experimental data. We also investigate the correspondence between the $\alpha$ cluster wave function and the $\alpha$ knockout cross section. The existing $^{20}$Ne($p$,$p\alpha$)$^{16}$O data at 101.5 MeV is well reproduced by the present framework. Due to the peripherality of the reaction, the surface region of the cluster wave function is selectively reflected to the knockout cross section. A quantitatively reliable $\alpha$ cluster wave function, $p$-$\alpha$ cross section, and distorting potentials between scattering particles, $\alpha$-$^{16}$O in particular, are crucial for the quantitative description of the ($p$,$p\alpha$) cross section. Due to the peripherality of the reaction, the ($p$,$p\alpha$) cross section is a good probe for the surface $\alpha$ amplitude.