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 12C at 7.458-MeV excitation energy, comprising a loose structure of three 𝛼 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 𝛾 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 𝛼 decay and the other with Gammasphere to measure 𝛾 decay of states in12C populated by 12N and 12B 𝛽 decay, respectively, we achieve high sensitivity to states in close proximity to the 𝛼 threshold in 12C.
Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit 𝛾-decay branching ratio is determined as a function of the 𝛽-decay feeding strength relative to the Hoyle state. In parallel, calculations of the 3𝛼 reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around 5×107 K.
Conclusion: From decay spectroscopy—at the 95% confidence limit, the Efimov state cannot exist at 7.458 MeV with any 𝛾-decay branching ratio unless the 𝛽 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 12C. Furthermore, the 3𝛼 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.
Purpose: Using a combination of 𝛾 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 𝛼 decay and the other with Gammasphere to measure 𝛾 decay of states in12C populated by 12N and 12B 𝛽 decay, respectively, we achieve high sensitivity to states in close proximity to the 𝛼 threshold in 12C.
Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit 𝛾-decay branching ratio is determined as a function of the 𝛽-decay feeding strength relative to the Hoyle state. In parallel, calculations of the 3𝛼 reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around 5×107 K.
Conclusion: From decay spectroscopy—at the 95% confidence limit, the Efimov state cannot exist at 7.458 MeV with any 𝛾-decay branching ratio unless the 𝛽 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 12C. Furthermore, the 3𝛼 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.
| Original language | English |
|---|---|
| Article number | L051303 |
| Number of pages | 5 |
| Journal | Physical Review C |
| Volume | 103 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - 17 May 2021 |