New narrow resonances observed in the unbound nucleus ${}^{15}\mathrm{F}$

The structure of the unbound ${}^{15}\mathrm{F}$ nucleus is investigated using the inverse kinematics resonant scattering of a radioactive ${}^{14}\mathrm{O}$ beam impinging on a ${\mathrm{CH}}_2$ target. The analysis of ${}^1\mathrm{H}({}^{14}\mathrm{O},\mathrm{p}){}^{14}\mathrm{O}$ and ${}^1\mathrm{H}({}^{14}\mathrm{O},2\mathrm{p}){}^{13}\mathrm{N}$ reactions allowed the confirmation of the previously observed narrow $1/2^{-}$ resonance, near the two-proton decay threshold, and the identification of two new narrow $5/2^{-}$ and $3/2^{-}$ resonances. The newly observed levels decay by 1p emission to the ground of ${}^{14}\mathrm{O}$, and by sequential 2p emission to the ground state of ${}^{13}\mathrm{N}$ via the $1^{-}$ resonance of ${}^{14}\mathrm{O}$. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the $5/2^{-}$ and $3/2^{-}$ resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function ${}^1\mathrm{H}({}^{14}\mathrm{O},\mathrm{p}){}^{14}\mathrm{O}$ and resonance spectrum in ${}^{15}\mathrm{F}$ are well reproduced in the unified framework of the GSM.

Figure 1

Differential cross section of the ${}^1\mathrm{H}({}^{14}\mathrm{O},\mathrm{p}){}^{14}\mathrm{O}$ reaction measured in the present study (full red dots) and in Ref. [15] (empty blue squares) and total cross section of the ${}^1\mathrm{H}({}^{14}\mathrm{O},2\mathrm{p}){}^{13}\mathrm{N}$ reaction (empty green circles), both as a function of the reconstructed resonance energy $E_r$ in the $p+{}^{14}\mathrm{O}$ system. For the latter, the contribution of the $5/2^{-}, 3/2^{-}$ states and higher-energy resonances extracted from the $R$-matrix fit are shown in filled blue, red, and green, respectively. The best $R$-matrix simultaneous fit of the two reaction channels constrained only by the g.s. properties extracted from Ref. [15] is shown as a continuous black line. The blue dashed line corresponds to the result of the GSMCC calculation (see text for details).

Figure 2

(a) Dalitz plot of the ${}^{13}\mathrm{N}+p+p$ decays from the $3/2^{-}$ state (${}^{13}\mathrm{N}-p$ vs $p-p$ reduced energies). The red (black) line corresponds to the first (second) proton emitted sequentially. (b) Center-of-mass angular distribution of the first proton, see Ref. [43] for the analysis method.

Figure 3

Level scheme of ${}^{15}\mathrm{F}$ with respect to ${}^{14}\mathrm{O}$ g.s. from the GSMCC calculation (left) and the present analysis (center), and level scheme of ${}^{14}\mathrm{O}$ (right). ${}^{15}\mathrm{F}$ data are taken from Ref. [15] and the present analysis, and ${}^{14}\mathrm{O}$ data are taken from Ref. [55]. Energies are in MeV. The red lines indicate the 2p- and 3p-decay thresholds. Resonance widths (in keV) are given in the brackets.