Electromagnetic transition from the 4$^+$ to 2$^+$ resonance in $^8$Be measured via the radiative capture in $^4$He+$^4$He

TL;DR

This paper presents a more precise measurement of the electromagnetic transition in beryllium-8, confirming its dumbbell shape and comparing results with advanced theoretical models.

Contribution

It provides a significantly more accurate measurement of the 4$^+$ to 2$^+$ transition in $^8$Be and compares experimental data with modern ab initio and cluster models.

Findings

Improved measurement accuracy by a factor of three.

Experimental results support the dumbbell-like shape of $^8$Be.

Comparison with theoretical models shows good agreement.

Abstract

An earlier measurement on the 4$^+$ to 2$^+$ radiative transition in $^8$Be provided the first electromagnetic signature of its dumbbell-like shape. However, the large uncertainty in the measured cross section does not allow a stringent test of nuclear structure models. The present paper reports a more elaborate and precise measurement for this transition, via the radiative capture in the $^4$He+$^4$He reaction, improving the accuracy by about a factor of three. The {\it ab initio} calculations of the radiative transition strength with improved three-nucleon forces are also presented. The experimental results are compared with the predictions of the alpha cluster model and {\it ab initio} calculations.