Particle decays of levels in ${}^{11,12}$N and ${}^{12}$O investigated with the invariant-mass method

Abstract

Particle-decaying states of the light nuclei ${}^{11,12}$N and ${}^{12}$O were studied using the invariant-mass method. The decay energies and intrinsic widths of a number of states were measured, and the momentum correlations of three-body decaying states were considered. A second 2$p$-decaying 2${}^{+}$ state of ${}^{12}$O was observed for the first time, and a higher energy ${}^{12}$O state was observed in the 4$p$+2$\hat{I}\pm$ decay channel. This 4$p$+2$\hat{I}\pm$ channel also contains contributions from fission-like decay paths, including ${}^6$Be${}_{g.s.}$+${}^6$Be${}_{g.s.}$. Analogs to these states in ${}^{12}$O were found in ${}^{12}$N in the 2$p$+${}^{10}$B and 2$p$+$\hat{I}\pm$+${}^6$Li channels. The momentum correlations for the prompt 2$p$ decay of ${}^{12}$O${}_{g.s.}$ were found to be nearly identical to those of ${}^{16}$Ne${}_{g.s.}$, and the correlations for the new 2${}^{+}$ state were found to be consistent with sequential decay through excited states in ${}^{11}$N. The momentum correlations for the 2${}_1^{+}$ state in ${}^{12}$O provide a new value for the ${}^{11}$N ground-state energy. The states in ${}^{12}$N/${}^{12}$O that belong to the $A$=12 isobaric sextet do not deviate from the quadratic isobaric multiplet mass equation (IMME) form.

16 pages, 16 figures, 7 tables, tables corrected