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

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.

6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review C