$2\alpha +t$ cluster structure in ${}^{11}$B

Abstract

The cluster structures of the excited states in ${}^{11}$B are studied by analyzing the isoscalar monopole and quadrupole strengths in the ${}^{11}$B($d$,$d^{\prime }$) reaction at $E_d=200$ MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the $3/2_3^{-}$ state at $E_x=8.56$ MeV is well described by the AMD calculation and is an evidence for a developed $2\alpha +t$ cluster structure.

Comments: Revised according to the referees' comments