A high-precision experiment in search of the predicted Efimov state in ${}^{12}\mathrm{C}$ at 7.458 MeV excitation energy was performed. Using a state-of-the-art detector system and novel analysis techniques, it was possible to isolate potential Efimov state events at the predicted energy level above the $3\alpha$ threshold with much better sensitivity in the ${}^{12}\mathrm{C}$ excitation energy spectrum compared to the existing data. The mutual ${}^8\mathrm{Be}$ resonance (91.84 keV) condition filters out a total of 21 probable Efimov state events around 7.458 MeV. With $2\sigma$ confidence, it gives an upper limit of $0.014\%$ for the Efimov state $\alpha$-decay branching ratio, which is about an order of magnitude smaller than the latest upper limit found in the literature. This observation was supported by a new penetrability calculation assuming a relatively extended structure for the Efimov state compared to the Hoyle state. However, the triple-$\alpha$ reaction rate, including both the Hoyle state and the Efimov state, was found to be much larger than the allowed limit, strongly suggesting that the Efimov-like state may not exist in ${}^{12}\mathrm{C}$.

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• Breakup reactions
• Few-body systems
• Low & intermediate energy heavy-ion reactions
• Nuclear astrophysics
• Nuclear reaction rates
• Nuclear reactions
• 6 ≤ A ≤ 19