The candidates of 2$\alpha$ condensate around the 16O nucleus studied by the real-time evolution method

TL;DR

This study uses the real-time evolution method to identify and analyze candidate 2α condensate states around 16O, providing clearer resonance identification and decay property predictions, supporting the existence of alpha condensation.

Contribution

The paper introduces the application of the real-time evolution method combined with ACCC to robustly identify 16O + 2α condensate states and predict their properties, improving upon previous theoretical approaches.

Findings

Identification of 0+3 and 0+4 states as candidates for 2α condensation.

Good agreement of transition strengths with previous predictions.

Feasible experimental observation due to small decay widths.

Abstract

Background: Searching for alpha condensation around a core nucleus, a new class of nuclear clustering, is an interesting topic. Previous theoretical studies predicted 16O + 2$\alpha$ condensed states. However, in those studies, the strong mixing with non-resonant states made the identification of true resonant states non-trivial. Purpose: To address this issue, we aim to provide a more robust theoretical verification of the 16O + 2$\alpha$ condensation. Our goal is to clearly identify the resonant states and predict their properties, such as decay widths. Method: We employ the real-time evolution method (REM), which generates physically important basis states using the equation of motion, minimizing contamination from the continuum. The analytical continuation in the coupling constant (ACCC) was used to estimate the $\alpha$-decay widths. Results: The present calculations show much better convergence of eigenstates, and the $0^+_3$ and $0^+_4$ states showed remarkable isoscalar monopole transition strengths, which were in good agreement with the predictions of Ichikawa et al. The small alpha-decay widths for these states suggest that experimental observation appears feasible. Conclusion: The present results show the reasonable agreement with a previous work, firmly establishing the $0^+_3$ and $0^+_4$ states approximately 5 and 1 MeV below the 16O + 2$\alpha$ threshold as candidates for the 2$\alpha$ condensation around the core nucleus 16O. The REM proved effective in identifying these states.