Ab initio calculations for nuclear pairing in oxygen isotopes*

Ab initio methods allow predictions to be made about the overall properties of nuclei directly from internuclear interactions. In this work, we employ the no-core configuration interaction (NCCI) approach to explore nuclear shell structure and pairing in oxygen isotopes. To understand how this structure contributes to the ab initio wavefunctions, we use the Lanczos decomposition method to obtain the decomposition of low-lying states with respect to the number and quasispin operators for each orbital in the valence neutron shell. The resulting decompositions allow us to see the extent to which the ab initio results follow the patterns expected from a simple shell-model interpretation.