High precision probe of the fully sequential decay width of the Hoyle state in ${}^{12}$C

Abstract

The decay path of the Hoyle state in ${}^{12}$C ($E_x=7.654\text{MeV}$) has been studied with the ${}^{14}\text{N}(\text{d},{\alpha }_2{)}^{12}\text{C}(7.654)$ reaction induced at $10.5\text{MeV}$. High resolution invariant mass spectroscopy techniques have allowed to unambiguously disentangle direct and sequential decays of the state passing through the ground state of ${}^8$Be. Thanks to the almost total absence of background and the attained resolution, a fully sequential decay contribution to the width of the state has been observed. The direct decay width is negligible, with an upper limit of $0.043\%$ ($95\%$ C.L.). The precision of this result is about a factor $5$ higher than previous studies. This has significant implications on nuclear structure, as it provides constraints to $3$-$\alpha$ cluster model calculations, where higher precision limits are needed.

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• Accuracy of the mean-field theory in describing ground-state properties of light nuclei
• Machine learning method for ${}^{12}$C event classification and reconstruction in the active target time-projection chamber
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• Two-body cluster entangled structure in the ${\mathcal{H}}_1\otimes {\mathcal{H}}_2$ Hilbert space
• A dynamical Interpretation of Sequential Decay in Reactive Scattering