Alpha-resonance structure in ${}^{11}$C studied via resonant scattering of ${}^7$Be+$\hat{I}\pm$ and ${}^7$Be($\hat{I}\pm$, $p$) reaction

Abstract

The resonance structure in ${}^{11}$C is particularly of interest with regard to the astrophysical ${}^7$Be($\hat{I}\pm$, ${\hat{I}}^3$) reaction, relevant at high temperature, and to the $\hat{I}\pm$-cluster structure in ${}^{11}$C. The measurement was to determine unknown resonance parameters for the high excited states of ${}^{11}$C. In particular, the $\hat{I}\pm$ decay width can be useful information to discuss $\hat{I}\pm$ cluster structure in ${}^{11}$C. New measurements of the ${}^7$Be+$\hat{I}\pm$ resonant scattering and the ${}^7$Be($\hat{I}\pm$, $p$)${}^{10}$B reaction in inverse kinematics were performed for center-of-mass energy up to 5.5 MeV, and the resonances at excitation energies of 8.9--12.7 MeV in the compound ${}^{11}$C nucleus were studied. Inelastic scattering of ${}^7$Be+$\hat{I}\pm$ and the ${}^7$Be($\hat{I}\pm$, $p_1$)${}^{10}$B${}^{\ast }$ reaction were also studied with a simultaneous ${\hat{I}}^3$-ray measurement. The measurements were performed at the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study (CNS), the University of Tokyo. We obtained excitation functions of ${}^7$Be($\hat{I}\pm$, $\hat{I}{\pm }_0$)${}^7$Be (elastic scattering), ${}^7$Be($\hat{I}\pm$, $\hat{I}{\pm }_1$)${}^7$Be${}^{\ast }$ (inelastic scattering), ${}^7$Be($\hat{I}\pm$, $p_0$)${}^{10}$B, and ${}^7$Be($\hat{I}\pm$, $p_1$)${}^{10}$B${}^{\ast }$. Many resonances including a new one were observed and their parameters were determined by an R-matrix analysis. The resonances we observed possibly enhance the ${}^7$Be($\hat{I}\pm$, ${\hat{I}}^3$) reaction rate but in a smaller magnitude than the lower-lying resonances. A new negative-parity cluster band, similar to the one previously suggested in the mirror nucleus ${}^{11}$B, is proposed.