Abstract
Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body subsystems. A hypothetical state in at 7.458-MeV excitation energy, comprising a loose structure of three particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally.
Purpose: Using a combination of spectroscopy, charged-particle spectroscopy, and astrophysical rate calculations allowing for strict limits on the existence of such a state to been established here.
Method: Using the combined data sets from two recent experiments, one with the TexAT (Texas Active Target) TPC (Time Projection Chamber) to measure decay and the other with Gammasphere to measure decay of states in populated by and decay, respectively, we achieve high sensitivity to states in close proximity to the threshold in .
Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit -decay branching ratio is determined as a function of the -decay feeding strength relative to the Hoyle state. In parallel, calculations of the reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around K.
Conclusion: From decay spectroscopy—at the 95% confidence limit, the Efimov state cannot exist at 7.458 MeV with any -decay branching ratio unless the strength is less than 0.7% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in . Furthermore, the reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.
- Received 22 December 2020
- Revised 6 February 2021
- Accepted 6 May 2021
DOI:https://doi.org/10.1103/PhysRevC.103.L051303
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