Deep hole state in $^{6}$He and its cluster structure

The deep-hole state in $^{6}$He was investigated via the quasifree $^7$Li(\textit{p},2\textit{p})$^6$He* reaction with decay coincidence measurements. In general, it is said that light nuclei are described not only by the shell model, but also by the cluster model. In order to investigate their structure, we have measured decay particles from deep-hole states in light nuclei because the direct decay process is dominant and its decay mode gives us imformation on the structure of deep-hole states. In this experiment, Triton decay was found to be dominant for the so-called \textit{s}-hole state in $^6$He contrary to the shell model calculation. This result implies the tri-nucleon cluster structure in $^{6}$He(\textit{s}-hole), which is created by knocking out a proton from an $\alpha$ in $^{7}$Li(gnd).