α-Particle Condensation in ¹⁶O Studied with a Full Four-Body Orthogonality Condition Model Calculation

To explore the four-α-particle condensate state in ¹⁶O, we solve a full four-body equation of motion based on the four-α-particle orthogonality condition model in a large four-α-particle model space spanned by Gaussian basis functions. A full spectrum up to the 0₆⁺ state is reproduced consistently with the lowest six 0⁺ states of the experimental spectrum. The 0₆⁺ state is obtained at about 2 MeV above the four-α-particle breakup threshold and has a dilute density structure, with a radius of about 5 fm. The state has an appreciably large α condensate fraction of 61%, and a large component of α+¹²C(0₂⁺) configuration, both features being reliable evidence for this state to be of four-α-particle condensate nature.