Multilevel Multichannel Study of the Structure ofN15from 12- to 14-MeV Excitation Energy

Measurements of the cross sections for the reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}\mathrm{}(p,p)\mathrm{}{}_{}{}^{14}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(p,{\alpha }_0){}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(p,n_0){}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(p,n_1){}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(p,{\gamma }_0){}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}(\alpha ,\alpha ){}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ have been made for incident particle energies of 2 to 4 MeV. Preliminary Legendre-polynomial analyses of measured angular distributions were used to guide a multilevel multichannel $R$-matrix analysis. In the $R$-matrix formulation a set of level parameters for eight resonances has been found which can account for the observed cross sections in all of the channels. The level at $E_x=13.42\mathrm{}$ MeV in ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ has been identified as the isobaric analog of the second excited state in ${}_{}{}^{15}{}_{}{}^{}\mathrm{C}$. The reduced widths of this level in the various channels indicate that it contains at least a 10% admixture of $T=\frac{1}{2}$. A series of strong $\alpha$-particle levels has been found which fit into the $\alpha$-particle core-excited threshold-state model scheme for ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$.