Alpha-decay of exited states in 12C

Recently it was suggested that the state in $^{12}$C at an excitation energy of 7.65 MeV ($J^\pi = 0^+$), the Hoyle state, can decay via a mechanism that produces three $\alpha$-particles of almost equal energy. High-resolution triple-$\alpha$ coincidence data were used to reconstruct the decay of the excited states in $^{12}$C at 7.65 MeV ($J^\pi = 0^+$) and 9.64 MeV ($J^\pi = 3^-$). These data were gathered at the Texas A\&M University K500 cyclotron facility, where a $^{10}$C beam impinged on a Be target and reaction products were detected using four Si $E-\Delta E$ detectors. The results of this experiment are consistent with the $\alpha$-particle decay of both levels proceeding exclusively through $^8 Be _{g.s.}$. In the first of these cases, the Hoyle state, upper limits of 0.45\% and 3.9\% (at the 99.75\% confidence level) are set for an equal-energy $\alpha$-particle decay process and a process uniformly spanning three-body phase space (respectively). The limit for the equal-energy $\alpha$-particle decay is much lower than claimed in the previous result.