Probing Nuclear forces beyond the drip-line using the mirror nuclei $^{16}$N and $^{16}$F

TL;DR

This study investigates the nuclear forces in mirror nuclei $^{16}$N and $^{16}$F by examining resonant states and proton-neutron interactions, revealing significant symmetry breaking due to continuum coupling effects.

Contribution

The paper provides new experimental data on proton-neutron interactions in unbound nuclei and explains symmetry breaking through continuum coupling effects.

Findings

Proton-neutron interaction strength varies by up to 40% between mirror nuclei.

Resonant states suggest a core plus proton and neutron configuration.

Continuum coupling significantly influences nuclear force symmetry.

Abstract

Radioactive beams of $^{14}$O and $^{15}$O were used to populate the resonant states 1/2$^+$, 5/2$^+$ and $0^-,1^-,2^-$ in the unbound $^{15}$F and $^{16}$F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in $^{16}$F can be viewed as a core of $^{14}$O plus a proton in the 2s$_{1/2}$ or 1d$_{5/2}$ shell and a neutron in 1p$_{1/2}$. Experimental energies were used to derive the strength of the 2s$_{1/2}$-1p$_{1/2}$ and 1d$_{5/2}$-1p$_{1/2}$ proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus $^{16}$N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an $\ell=0$ proton configuration.