Structure of the Hoyle State of ¹²C Extracted from Reaction Observables

Abstract

The Hoyle state of 12 C has intensively been studied theoretically and experimentally. Despite a rather clear understanding of its three-α cluster structure, the description of the Hoyle state appeared in reaction observables has not been achieved. It was reported in many studies that the (α,α ′ ) cross section theoretically obtained with using the transition density of 12 C from the ground state to the 0 + 2 state significantly overshot the measured cross section. This discrepancy is called the missing monopole strength of the Hoyle state. To solve this probelm, we apply a fully microscopic framework to the (α,α ′ ) inelastic scattering to the 0 + 2 state of 12 C, and show that the calculated result agrees with the measured cross section. We find the consistency between the monopole strength of the Hoyle state determined by structural calculation and that extracted from reaction observables. We thus show essentially there is no room for the missing monopole strength.