Existence of core excited 8Be* = α + α* cluster structure in α + α scattering

Abstract

Abstract We show the existence of the $\alpha+\alpha^*$ cluster structure at the highly excited energy around $E_x=20$ MeV in $^{8}$Be for the first time in the coupled-channel calculations. An extended double-folding model derived using a realistic precise cluster wave function with a well-developed $N+3N$ cluster structure for the first excited state of $^4$He was employed. The calculation reproduces the experimental phase shifts in $\alpha + \alpha$ scattering up to $E_{\rm c.m.}=21$ MeV well. The result shows that the well-developed core-excited $\alpha+\alpha^*$ structure appears as resonances for $L=0$ and $2$ near the $\alpha+\alpha^*$ threshold which correspond to the experimental states at $E_x=20.20$ MeV and $E_x=22.24$ MeV in $^8$Be.