Radiative Width of the Hoyle State from 
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-Ray Spectroscopy

Kibédi, T.; Alshahrani, B.; Stuchbery, A.E.; Larsen, A. C.; Görgen, A.; Siem, S.; Guttormsen, M.; Giacoppo, F.; Morales, A. I.; Şahin, E.; Tveten, G. M.; Garrote, F. L. Bello; Klintefjord, M.; Maharramova, Sabina; Nyhus, H. T.; Tornyi, T.; Renstrøm, T.; Paulsen, W.

doi:10.1103/physrevlett.125.182701

“…A recent measurement [49] of the radiative branching ratio, Γ rad /Γ, suggests a value that is substantially higher than the currently adopted ratio used in this work. Combining this recent result with the present measurement on Γ E0 π /Γ, results in a large increase of the radiative width as compared to the adopted value.…”

Section: Discussionmentioning

confidence: 56%

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

Kibédi¹,

Reed²,

Stuchbery³

et al. 2020

Preprint

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Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α particles fuse to form 12 C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the α threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the E0 decay branching ratio of the Hoyle state, and the current 10% uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The rate of the 3α process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models.Purpose: To deduce a new, more precise value for the E0 decay branching ratio of the Hoyle state.Method: The E0 branching ratio was deduced from a series of pair conversion measurements of the E0 and E2 transitions depopulating the 0 + 2 Hoyle state and 2 + 1 state in 12 C, respectively. The excited states were populated by the 12 C(p, p ) reaction at 10.5 MeV beam energy, and the pairs were detected with the electron-positron pair spectrometer, Super-e, at the Australian National University. The deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the 2 + 1 state in the reaction. For this purpose, proton scattering and γ-ray angular distribution experiments were also performed.Results: An E0 branching ratio of Γ E0 π /Γ = 8.2(5) × 10 −6 was deduced in the current work, and an adopted value of Γ E0 π /Γ = 7.6(4) × 10 −6 is recommended based on a weighted average of previous literature values and the new result. Conclusions:The new recommended value for the E0 branching ratio is about 14% larger than the previous adopted value of Γ E0 π /Γ = 6.7(6) × 10 −6 , while the uncertainty has been reduced from 9% to 5%. The new result reduces the radiative width, and hence 3α reaction rate, by 11% relative to the adopted value, and the uncertainty to 6.1%. This reduction in width and increased precision is likely to constrain possible outcomes of astrophysical calculations.

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“…Oxygen production occurs later by α-capture on the freshly produced 12 C (the O→C transition at the innermost edge of R2). Current estimates of the uncertainty in the 3α reaction rate are 30% over the regions of typical astrophysical interest (Kibédi et al 2020). However, at lower temperatures ( 0.1 GK), the uncertainty is likely much larger, because other reaction mechanisms become significant (Suno et al 2016).…”

Section: α Reaction Rate Probability Distribution Functionmentioning

confidence: 99%

On Trapped Modes in Variable White Dwarfs as Probes of the ¹²C(α, γ)¹⁶O Reaction Rate

Chidester

¹

,

Farag

²

,

Timmes

³

2022

ApJ

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We seek signatures of the current experimental 12C α , γ 16 O reaction rate probability distribution function in the pulsation periods of carbon–oxygen white dwarf (WD) models. We find that adiabatic g-modes trapped by the interior carbon-rich layer offer potentially useful signatures of this reaction rate probability distribution function. Probing the carbon-rich region is relevant because it forms during the evolution of low-mass stars under radiative helium-burning conditions, mitigating the impact of convective mixing processes. We make direct quantitative connections between the pulsation periods of the identified trapped g-modes in variable WD models and the current experimental 12C α , γ 16 O reaction rate probability distribution function. We find an average spread in relative period shifts of ΔP/P ≃ ±2% for the identified trapped g-modes over the ±3σ uncertainty in the 12C α , γ 16 O reaction rate probability distribution function—across the effective temperature range of observed DAV and DBV WDs and for different WD masses, helium shell masses, and hydrogen shell masses. The g-mode pulsation periods of observed WDs are typically given to six to seven significant figures of precision. This suggests that an astrophysical constraint on the 12C α , γ 16 O reaction rate could, in principle, be extractable from the period spectrum of observed variable WDs.

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“…To this end, there have been years of continuous effort to reduce experimental uncertainties. Two recent experiments have determined new values for Γ E0 π /Γ (14% higher than the previous adopted value) [12] and Γ rad /Γ (50% higher than the previous adopted value) [10]. When combined with the currently adopted Γ E0 π value, these new experiments resulted in Γ rad = 5.1(6) × 10 −3 eV.…”

Section: Introductionmentioning

confidence: 99%

“…The Hoyle state disintegrates back to 8 Be+α or 3α with probability > 99.94% [9,10]. Stable carbon is only produced when the Hoyle state instead electromagnetically decays directly to the ground state via an electric monopole (E0) transition, or via the 2 + 1 state by two electric quadrupole (E2) transitions.…”

Section: Introductionmentioning

confidence: 99%

High precision proton angular distribution measurements of $^{12}$C(p,p') for determination of the $E0$ decay branching ratio of the Hoyle state

Cook,

Chevis,

Eriksen

et al. 2022

Preprint

0

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Background In stellar environments, carbon is produced exclusively via the 3α process, where three α particles fuse to form 12 C in the excited Hoyle state, which can then decay to the ground state. The rate of carbon production in stars depends on the radiative width of the Hoyle state. While not directly measurable, the radiative width can be deduced by combining three separately measured quantities, one of which is the E0 decay branching ratio. The E0 branching ratio can be measured by exciting the Hoyle state in the 12 C(p, p ) reaction and measuring the pair decay of both the Hoyle state and the first 2 + state of 12 C.Purpose To reduce the uncertainties in the carbon production rate in the universe by measuring a set of proton angular distributions for the population of the Hoyle state (0 + 2 ) and 2 + 1 state in 12 C in 12 C(p, p ) reactions between 10.20 and 10.70 MeV, used in the determination of the E0 branching ratio of the Hoyle state.Method Proton angular distributions populating the ground, first 2 + , and the Hoyle states in 12 C were measured in 12 C(p,p') reactions with a silicon detector array covering 22 • < θ < 158 • in 14 small energy steps between 10.20 and 10.70 MeV with a thin (60 µg/cm 2 ) nat C target.Results Total cross-sections for each state were extracted and the population ratio between the 2 + 1 and Hoyle state determined at each energy step. By appropriately averaging these cross-sections and taking their ratio, the equivalent population ratio can be extracted applicable for any thick 12 C target that may be used in pair-conversion measurements. This equivalent ratio agreed with a direct measurement performed with a thick target.Conclusions We present a general data set of high-precision 12 C(p, p ) cross-sections that make uncertainties resulting from the population of the 2 + 1 and 0 + 2 states by proton inelastic scattering negligible for any future measurements of the E0 branching ratio in 12 C. Implications for future measurements are discussed, as well as possible applications of this data set for investigating cluster structures in 13 N.

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Radiative Width of the Hoyle State from γ -Ray Spectroscopy

Cited by 37 publications

References 41 publications

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

On Trapped Modes in Variable White Dwarfs as Probes of the ¹²C(α, γ)¹⁶O Reaction Rate

High precision proton angular distribution measurements of $^{12}$C(p,p') for determination of the $E0$ decay branching ratio of the Hoyle state

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Radiative Width of the Hoyle State from γ -Ray Spectroscopy

Cited by 37 publications

References 41 publications

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

Improved precision on the experimental E0 decay branching ratio of the Hoyle state

On Trapped Modes in Variable White Dwarfs as Probes of the 12C(α, γ)16O Reaction Rate

High precision proton angular distribution measurements of $^{12}$C(p,p') for determination of the $E0$ decay branching ratio of the Hoyle state

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On Trapped Modes in Variable White Dwarfs as Probes of the ¹²C(α, γ)¹⁶O Reaction Rate