Neutron Knockout to Probe 3N Forces in the Ca Isotopes

Recent calculations by Holt et al. [1] have suggested that the inclusion of 3N forces to describe the structure of neutron-rich Ca isotopes provides a more realistic description of the nuclear structure. Mass measurements have confirmed the importance of including 3N forces compared to NN-only interactions, but cannot discriminate between the predictions of phenomenological interactions and the NN+3N microscopic calculations. Neutron knockout along the $Z$=20 isotopes provides an opportunity to test the results of NN+3N calculations against phenomenological interactions. The calculations of Holt et al. predict a fragmentation of the 1$f_{7/2}$ neutron strength from the first 7/2- state in $^{49}$Ca into higher lying states, in contrast to the predictions of both GXPF1 and KB3G which concentrate the strength in the lowest lying 7/2- state. Differences are also observed in the summed $f_{7/2}$ strength to bound nuclear states in both $^{50}$Ca and $^{49}$Ca neutron knockout. We will report on a systematic study of one-neutron knockout along the Ca isotopes using GRETINA + S800. Comparison of experimental spectroscopic factors to calculations will provide insight into the role of 3N forces in describing the $Z$=20 isotopes.\\[4pt] [1] J. Holt et al., J. Phys. G 39, 085111 (2012).