Invariant mass spectroscopy of $^{17}$C via one-neutron knockout reaction from $^{18}$C

The nuclei away from the $\beta$-stability line are expected to have exotic nuclear structures. For example, the ground states of neutron-rich carbon isotopes, $^{15}$C, $^{17}$C, and $^{19}$C, have been predicted to be 5/2$^{+}$ states in the naive shell model. However, they were identified as 1/2$^{+}$, 3/2$^{+}$, and 1/2$^{+}$, respectively, due to the halo structure and/or nuclear deformation. To understand the properties of the valence orbit relative to the inner orbit in those neutron-rich carbon isotopes, the study of the negative parity states is decisive. The present study focuses on the low-lying negative parity states in $^{17}$C above the neutron decay threshold. The experiment was performed for the C($^{18}$C,$^{17}$C$^*$) one-neutron knockout reaction channel at 250 MeV/nucleon using the SAMURAI spectrometer at RIKEN-RIBF, during the first physics runs of the apparatus. The nucleon knockout reaction utilizing the secondary beams in inverse kinematics has become recognized as a sensitive tool for spectroscopy of the nuclei far from the $\beta$-stability line. In the presentation, details of the measurement and analysis will be reported together with new results on the low-lying negative parity states in $^{17}$C.