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

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