Precise measurement of the $\gamma$-decay probability of the Hoyle state with a new triple coincidence-detection method

We measured the $\gamma$-decay probability of the Hoyle state with a new method of triple coincidence detection of a scattered $\alpha$ particle, a recoil ${}^{12}\mathrm{C}$ nucleus, and a $\gamma$ ray in inelastic alpha scattering on ${}^{12}\mathrm{C}$. This method successfully enabled a low-background measurement and a precise determination of the $\gamma$-decay probability of the Hoyle state as ${\mathrm{\Gamma }}_{\gamma }\mathrm{/}\mathrm{\Gamma }=[4.00\pm 0.22(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.})\pm 0.18(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.})]\times {10}^{-4}$, which is consistent with the previous literature value. Therefore, we concluded that the literature value can be reliably used in the study of nucleosynthesis in the universe.