Radiative Decay Branching Ratio of the Hoyle State in ¹²C via Charged Particle Coincidence Techniques

¹ Dipartimento di Fisica “Ettore Pancini”, University of Napoli “Federico II”, Napoli, Italy
² INFN Sezione di Napoli, Napoli, Italy
³ Dipartimento di Fisica e Astronomia “Ettore Majorana”, University of Catania, Catania, Italy
⁴ INFN Sezione di Catania, Catania, Italy
⁵ INFN Laboratori Nazionali di Legnaro, Legnaro, Italy
⁶ Dipartimento di Fisica, University of Padova, Padova, Italy
⁷ INFN Sezione di Padova, Padova, Italy
⁸ Dipartimento di Fisica e Astronomia, University of Firenze, Sesto Fiorentino, Italy
⁹ INFN Sezione di Firenze, Sesto Fiorentino, Italy
¹⁰ INFN Laboratori Nazionali del Sud, Catania, Italy
¹¹ Zavod za eksperimentalnu fiziku, Rudjer Boškovic´ Institute, Zagreb, Croatia
¹² INFN Sezione di Roma Tre, Roma, Italy

^* e-mail: daniele.dellaquila@unina.it

Published online: 28 October 2024

Abstract

The properties of the Hoyle state in ¹²C (7.654 MeV, 0⁺) affect the rate at which carbon, one of the most abundant elements in the Universe, is forged in stars. Recent experiments reported values of its radiative decay branching ratio that are in tension, posing major implications especially in the astrophysical domain. This work reports on an almost background-free measurement of the radiative decay branching ratio of the Hoyle state that exploits charged particle coincidence techniques. The experiment adopts several methodologies to minimize the background and identify the rare signal associated with the radiative decay. Large care is devoted to having under full control two of the major sources of systematic errors in particle-coincidence experiments: the coincidence efficiency and the spurious coincidence rate. We find a radiative decay branching ratio of Γ_rad/Γ_tot = 4.2(6) · 10⁻⁴. The new finding helps to resolve the tension between recent data published in the literature.