DREB Conference 2024

The proton-induced $\alpha$ knockout reaction, ($p,p\alpha$), is a powerful probe of the $\alpha$ formation in nuclei. It has been shown that a modern theoretical calculation of the $\alpha$ amplitude in the ${}^{20}$Ne ground state combined with the ($p,p\alpha$) reaction calculation by the distorted wave impulse approximation can quantitatively reproduce the experimental data [1]. On the other hand, quantitative reproductions of the $\alpha$ knockout cross section from medium to heavy nuclei are still challenging [2]. Stimulated by the theoretical prediction [3] and the $\alpha$ knockout reaction experiment of Sn isotopes [4], the universality of the $\alpha$ formation throughout the nuclear chart is also an interesting subject.
In this contribution, from a reaction theory point of view, I will present the recent progress in the $\alpha$ formation phenomena studied by the ($p,p\alpha$) reaction and our recent achievement which showed the possibility that the $\alpha$ knockout reaction may be a good probe for the $\alpha$ formation on the surface of the $\alpha$ decay nuclei [4]. I will also discuss the future perspectives of the $\alpha$ knockout reaction with regard to the ONOKORO project, which is being carried out mainly at RIKEN, RCNP and HIMAC in Japan.

[1] K. Yoshida et al., Phys. Rev. C 94, 044604 (2016) [arXiv:1603.00638].
[2] Yasutaka Taniguchi et al., Phys. Rev. C 103, L031305 (2021). [arXiv:2101.04820].
[3] S. Typel, Phys. Rev. C 89, 064321 (2014).
[4] Junki Tanaka et al., Science 371, 260 (2021).
[5] Kazuki Yoshida and Junki Tanaka, Phys. Rev. C 106, 014621 (2022). [arXiv:2111.07541]