Search for the First Excited State of $^{24}$O

The location of the first 2$^+$ excited state of $^{24}$O is important evidence for the doubly magic nature of this nucleus predicted by shell model calculations. Previous searches for the first excited state of $^{24}$O utilizing in-beam $\gamma$-ray spectroscopy have been unsuccessful indicating that the state is located above the neutron separation energy. We populated states in $^{24}$O by two-proton knockout from a beam of $^{26}$Ne. Neutrons were detected by the Modular Neutron Array MoNA in coincidence with $^{23}$O fragments deflected by the MSU/FSU sweeper magnet and detected in a set of charged-particle detectors. The decay energy and thus the location of unbound excited states can be reconstructed from the measured energies and angles of the $^{23}$O fragments and the neutrons.