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The recent discovery and spectroscopic measurements of${}^{27}\mathrm{O}$and${}^{28}\mathrm{O}$suggests the disappearance of the$N=20$shell structure in these neutron-rich oxygen isotopes.

We measured one- and two-proton removal cross sections from${}^{27}\mathrm{F}$and${}^{29}\mathrm{Ne}$, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations.

The invariant mass technique was used to reconstruct the two-body (${}^{24}\mathrm{O}+n$) and three-body (${}^{24}\mathrm{O}+2n$) decay energies from knockout reactions of${}^{27}\mathrm{F}$(106.2 MeV/u) and${}^{29}\mathrm{Ne}$(112.8 MeV/u) beams impinging on a${}^9\mathrm{Be}$target.

The one-proton removal from${}^{27}\mathrm{F}$strongly populated the ground state of${}^{26}\mathrm{O}$and the extracted cross section of$3.4_{-1.5}^{+0.3}$mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from${}^{29}\mathrm{Ne}$an upper limit of 0.08 mb was extracted for populating states in${}^{27}\mathrm{O}$decaying though the ground state of${}^{26}\mathrm{O}$.

The measured upper limit for the population of the ground state of${}^{26}\mathrm{O}$in the two-proton removal reaction from${}^{29}\mathrm{Ne}$indicates a significant difference in the underlying nuclear structure of${}^{27}\mathrm{F}$and${}^{29}\mathrm{Ne}$.