α-resonance structure in11C studied via resonant scattering of7Be+αand with the7Be(α,p) reaction

Background: The resonance structure in ${}^{11}$C is of particular interest with regard to the astrophysical ${}^{7}$Be($\ensuremath{\alpha},\ensuremath{\gamma}$) reaction, relevant at high temperature, and to the $\ensuremath{\alpha}$-cluster structure in ${}^{11}$C.Purpose: The measurement was made to determine the unknown resonance parameters for the high excited states of ${}^{11}$C. In particular, the $\ensuremath{\alpha}$-decay width can be useful information to discuss the $\ensuremath{\alpha}$-cluster structure in ${}^{11}$C.Methods: New measurements of ${}^{7}\mathrm{Be}+\ensuremath{\alpha}$ resonant scattering and the ${}^{7}$Be($\ensuremath{\alpha},p$)${}^{10}$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 ${}^{7}\mathrm{Be}+\ensuremath{\alpha}$ and the ${}^{7}$Be($\ensuremath{\alpha},p$${}_{1}$)${}^{10}$B${}^{*}$ reaction were also studied with a simultaneous $\ensuremath{\gamma}$-ray measurement. The measurements were performed at the low-energy radioactive ion beam facility CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo.Results: We obtained excitation functions of ${}^{7}$Be($\ensuremath{\alpha},{\ensuremath{\alpha}}_{0}$)${}^{7}$Be (elastic scattering), ${}^{7}$Be($\ensuremath{\alpha},{\ensuremath{\alpha}}_{1}$)${}^{7}$Be${}^{*}$ (inelastic scattering), ${}^{7}$Be($\ensuremath{\alpha},p$${}_{0}$)${}^{10}$B, and ${}^{7}$Be($\ensuremath{\alpha},p$${}_{1}$)${}^{10}$B${}^{*}$. Many resonances including a new one were observed and their parameters were determined by using an $R$-matrix analysis.Conclusions: The resonances we observed possibly enhance the ${}^{7}$Be($\ensuremath{\alpha},\ensuremath{\gamma}$) reaction rate but with 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.