Investigation on $\alpha$ clustering through knockout reaction

摘要

Our goal is to reveal how the $\alpha$ cluster amplitude is probed through$\alpha$ knockout reactions depending on reaction conditions, e.g., theincident energy. We consider $^{20}$Ne($p$,$p\alpha$)$^{16}$O and$^{120}$Sn($p$,$p\alpha$)$^{116}$Cd at 100-400 MeV within the distorted waveimpulse approximation (DWIA) framework. We introduce a masking function whichshows how the reaction amplitude in the nuclear interior is suppressed anddefines the probed region of the $\alpha$ cluster wave function. It is clearlyshown by means of the masking function that the $\alpha$ knockout reactionprobes the $\alpha$ cluster amplitude in the nuclear surface region, which isthe direct measure of well-developed $\alpha$ cluster states. A simplified formof the masking function is introduced and the incident energy dependence of themasking effect is investigated. $\alpha$ knockout reaction can probe the$\alpha$ cluster amplitude in the nuclear surface region by choosing properkinematics owing to the masking effect originated from absorptions ofdistorting potentials, and is a suitable method to investigate how $\alpha$cluster states are spatially developed.