Validity of pair truncation of the nuclear shell model in 46Ca

We study the validity of pair truncation of the nuclear shell model by using the semimagic nucleus Ca-46. We present low-lying states and their E2 transition rates based on both nucleon pair approximation (NPA) and exact shell-model (SM) calculations. We also calculate overlaps between wave functions of low-lying states calculated by using the NPA and those calculated by using the SM. Our calculated results show a remarkable agreement between the NPA results and the SM results, although the NPA is a drastic truncation of the SM.