Radiative Width of the Hoyle State from γ-Ray Spectroscopy

Abstract

The cascading 3.21 and 4.44 MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65 MeV excitation energy in 12 C , excited by the 12 C ( p , p ′ ) reaction at 10.7 MeV proton energy. From the proton- γ − γ triple coincidence data, a value of Γ rad / Γ = 6.2 ( 6 ) x 10 − 4 was obtained for the radiative branching ratio. Using our results, together with Γ E 0 π / Γ from Eriksen et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted Γ π ( E 0 ) values, the radiative width of the Hoyle state is determined as Γ rad = 5.1 ( 6 ) x 10 − 3 eV . This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.