Invariant-mass spectroscopy of ${}^{14}$O excited states

Abstract

Excited states in ${}^{14}$O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast ${}^{15}$O beam and the invariant-mass technique was employed to isolate the 1$p$ and 2$p$ decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2${}^{+}$ state that we find is in near degeneracy with the third 0${}^{+}$ state. An interesting case of sequential 2$p$ decay through a pair of degenerate ${}^{13}$N excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons.

19 pages, 20 figures