Observation of narrow states in nuclei beyond the proton drip line: 15F and 16Ne

Abstract

Two high-lying states in 15F and 16Ne, unbound with respect to one-proton (1p) and two-proton (2p) emissions, have been observed in the fragmentation of 17Ne at intermediate energies. They undergo mainly sequential emissions of protons via intermediate states in 14O and 15F and have decay energies of 7.8(2) and 7.6(2) MeV, respectively. The widths of the newly observed states in 15F and 16Ne are much smaller than the Wigner limits for single-particle configurations, of 0.4(4) and 0.8(+8-4) MeV, respectively. In addition, narrow widths of 0.2(2) MeV are derived for two other high-lying states in 15F with Qp of 4.9 and 6.4 MeV, which match features of the recently predicted narrow odd-parity 15F states with two valence protons in the sd shell. All energies and widths have been obtained by analyzing angular correlations of the decay products, p-p-14O and p-p-13N, whose trajectories have been measured by a tracking technique with silicon microstrip detectors.