Knockout reaction for exotic nuclei with recoil proton tagging, Y. L. Ye, Peking University, China − We report the discrimination of the core fragment knockout and the valence nucleon knockout reaction mechanisms at medium energy range, by the use of the recoil proton tagging technique.   Results for ⁸He at 82.3 MeV/u were obtained from an experiment carried out at RIKEN, for both Hydrogen and Carbon targets.  Recoil protons were detected in coincidence with the forward moving core fragments and neutrons. The core fragment knockout mechanism is identified through the polar angle correlation and checked by various kinematics relations.  This mechanism may be used to extract the cluster structure information of unstable nuclei.  On the other hand, with the selection of the tagged valence nucleon knockout mechanism, a narrower peak of ⁷He ground state is obtained.  The extracted neutron spectroscopic factor is relatively smaller than the no-tagged one, and is in good agreement with the prediction of ab initio Green’s function Monte Carlo calculations.  In the case of Carbon target possible complex reaction processes, which might affect the extraction of the structure information, are discussed based on measurements and some theoretical calculations.