Probing nuclear forces beyond the drip-line using the mirror nuclei ¹⁶N and ¹⁶F

Radioactive beams of ¹⁴O and ¹⁵O were used to populate the resonant states 1/2⁺, 5/2⁺ and 0^-,1^-,2^- in the unbound ¹⁵F and ¹⁶F nuclei, respectively, by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in ¹⁶F can be viewed as a core of ¹⁴O 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 ¹⁶N, and the latter changes 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 l = 0 proton configuration. (authors)