Clarifying the radiative decay of the Hoyle state with charged-particle spectroscopy

Abstract

A detailed knowledge of the decay properties of the so called Hoyle state in the $_{}^{12}$ C nucleus ( $E_x=7.654$ MeV, $0^{+}$ ) is required to calculate the rate at which carbon is forged in typical red-giant stars. This paper reports on a new almost background-free measurement of the radiative decay branching ratio of the Hoyle state using advanced charged particle coincidence techniques. The exploitation, for the first time in a similar experiment, of a bidimensional map of the coincidence efficiency allows to reach an unitary value and, consequently, to strongly reduce sources of systematic uncertainties. The present results suggest a value of the radiative branching ratio of ${\Gamma }_{\mathrm{rad}}/{\Gamma }_{\mathrm{tot}}=4.4\left(6\right)·{10}^{-4}$ . This finding helps to resolve the tension between recent data published in the literature.