Quenching of Spectroscopic Factors for Proton Removal in Oxygen Isotopes

We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes ${}^{14,16,22,24,28}\mathrm{O}$ with a chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds.

Figure 1

Normalized spectroscopic factors for $p_{1/2}$ and $p_{3/2}$ proton removal from the oxygen isotopes ${}^{14,16,22,24,28}\mathrm{O}$. The continuum states included in the calculation (HF-WS) lead to a dramatic quenching of the spectroscopic factors as the neutron dripline is approached. For comparison, we show calculations of spectroscopic factors using a HF basis built entirely from harmonic oscillator basis functions (HF-OSC).

Figure 2

Ratio of the radial overlap functions $⟨{}^{13}\mathrm{N}|a_{lj}|{}^{14}\mathrm{O}⟩$, $⟨{}^{15}\mathrm{N}|a_{lj}|{}^{16}\mathrm{O}⟩$, $⟨{}^{21}\mathrm{N}|a_{lj}|{}^{22}\mathrm{O}⟩$, $⟨{}^{23}\mathrm{N}|a_{lj}|{}^{24}\mathrm{O}⟩$, and $⟨{}^{27}\mathrm{N}|a_{lj}|{}^{28}\mathrm{O}⟩$ for the $p_{1/2}$ single-particle state.

Figure 3

Plot of calculated SFs as functions of the difference between the calculated neutron and proton separation energies. The results are for the single-particle states closest to the Fermi surface. For protons these are the $p_{1/2}$ states.