Complete kinematical study of the 3$\alpha$ breakup of the 16.11 MeV state in ${}^{12}$C

Abstract

The reaction ${}^{11}B+p$ has been used to populate the $(J^{\pi },T)=(2^{+},1)$ state at an excitation energy of 16.11 MeV in ${}^{12}$C, and the breakup of the state into three $\alpha$ particles has been studied in complete kinematics. A two-step breakup model which includes interference effects is found to provide the most accurate description of the experimental data. The branching ratio to the ground state of ${}^8$Be is determined to be 5.1(5)% in agreement with previous findings, but more precise by a factor of two, while the decay to the first-excited state in ${}^8$Be is found to be dominated by $d$-wave emission.

11 pages, 8 figures