One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at Edecay=50$pm$3 keV, corresponding to an excited state in 23O at 2.78$pm$0.11 MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d -wave neutron knockout, providing support for a J{pi} assignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1$pm$0.4 by comparing the measured cross section (View the MathML source) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24O.
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