Radiative Width of the Hoyle State from γ-Ray Spectroscopy.

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 C-12, excited by the C-12(p, p') reaction at 10.7 MeV proton energy. From the proton-gamma-gamma triple coincidence data, a value of Gamma(rad)/Gamma = 6.2(6) x 10(-4) was obtained for the radiative branching ratio. Using our results, together with Gamma(E0)(pi)/Gamma from Erikson et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted Gamma(pi)(E0) values, the radiative width of the Hoyle state is determined as Gamma(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.