Investigating the alpha-clustering on the surface of $^{120}$Sn via ($p$,$palpha$) reaction and the validity of the factorization approximation

The $^{120}$Sn($p$,$palpha$)$^{116}$Cd reaction at 392 MeV is investigated with the distorted wave impulse approximation (DWIA) framework. We show that this reaction is very peripheral mainly because of the strong absorption of $alpha$ by the reaction residue $^{116}$Cd, and the $alpha$-clustering on the nuclear surface can be probed clearly. We investigate also the validity of the so-called factorization approximation that has frequently been used so far. It is shown that the kinematics of $alpha$ in the nuclear interior region is significantly affected by the distortion of $^{116}$Cd, but it has no effect on the reaction observables because of the strong absorption in that region.