Quantitative description of the Ne 20 (p,pα) O 16 reaction as a means of probing the surface α amplitude

Background: The proton-induced α knockout reaction has been utilized for decades to investigate the α cluster formation in the ground state of nucleus. However, even today, the theoretical description of the reaction is not precise enough for the quantitative study. For example, the α spectroscopic factors reduced from α knockout experiments with reaction analyses using phenomenological α cluster wave functions disagree with those given by a structure theory. In some cases they also scatter depending on the kinematical condition of the experiment. This suggests that the theoretical description of the α knockout reaction is insufficient from a quantitative viewpoint. Purpose: We show that the distorted wave impulse approximation can describe Ne20(p,pα)O16 reaction quantitatively if reliable inputs are used; the optical potential, the p-α cross section, and the α cluster wave function. We also investigate the relationship between the α cluster wave function and the α knockout cross section. Method: The Ne20(p,pα)O16 reaction is described by the distorted wave impulse approximation. An input of the calculation, the α-O16 cluster wave function, is obtained by the antisymmetrized molecular dynamics and the Laplace expansion method. Results: In contrast to the previous work, the Ne20(p,pα)O16 data at 101.5 MeV is successfully reproduced by the present framework without any free adjustable parameters. It is also found that the knockout cross section is sensitive to the surface region of the cluster wave function because of the peripherality of the reaction. Conclusions: Using a reliable α cluster wave function, p-α cross section, and distorting potentials, it is found that the Ne20(p,pα)O16 cross section is quantitatively reproduced by the present framework. This success demonstrates that the proton-induced α knockout reaction is a quantitative probe for the α clustering.