研究预测的霍伊尔状态的呼吸模式激发
Investigating the predicted breathing-mode excitation of the Hoyle state
摘要：
了解$\mathrm{^{12}C}$ $-$（霍伊尔态，特别是$-$）中的低单极强度对于我们理解天体物理学上重要的$3α$反应和$α$ -粒子聚集至关重要。多个理论模型已经预测了霍伊尔态在$E_{x} \approx 9$ MeV的呼吸模式，对应于底层$α$簇的径向同相振荡。采用$\mathrm{^{12}C}(α, α^{\prime})\mathrm{^{12}C}$和$\mathrm{^{14}C}(p, t)\mathrm{^{12}C}$反应来填充$^{12}$ C中的状态，以便搜索该预测的呼吸模式。自洽的，同时分析的包容性光谱与R-矩阵线形，连同角分布的带电粒子衰变，产生了明确的证据，过剩的电子束强度在$E_{x} \approx 9$兆电子伏，这是高度集体。使用拟合再现实验观察到的包容性产量，对于各种广泛的状态具有一致的人口比例，需要额外的能量来源。将这种额外的共振解释为霍伊尔态的呼吸模式激发，将提供支持霍伊尔态本身的$\mathcal{D}_{3h}$对称性的证据。过量的质子强度可能会使霍伊尔态的性质分析复杂化，从而改变了在$T_{9} \gtrsim 2$下$3α$速率的温度依赖性，并最终改变了爆炸恒星中预测的核合成。
英文摘要：
Knowledge of the low-lying monopole strength in $\mathrm{^{12}C}$ $-$ the Hoyle state in particular $-$ is crucial for our understanding of both the astrophysically important $3α$ reaction and of $α$-particle clustering. Multiple theoretical models have predicted a breathing mode of the Hoyle State at $E_{x} \approx 9$ MeV, corresponding to a radial in-phase oscillation of the underlying $α$ clusters. The $\mathrm{^{12}C}(α, α^{\prime})\mathrm{^{12}C}$ and $\mathrm{^{14}C}(p, t)\mathrm{^{12}C}$ reactions were employed to populate states in $^{12}$C in order to search for this predicted breathing mode. A self-consistent, simultaneous analysis of the inclusive spectra with R-matrix lineshapes, together with angular distributions of charged-particle decay, yielded clear evidence for excess monopole strength at $E_{x} \approx 9$ MeV which is highly collective. Reproduction of the experimentally observed inclusive yields using a fit, with consistent population ratios for the various broad states, required an additional source of monopole strength. The interpretation of this additional monopole resonance as the breathing-mode excitation of the Hoyle state would provide evidence supporting a $\mathcal{D}_{3h}$ symmetry for the Hoyle state itself. The excess monopole strength may complicate analysis of the properties of the Hoyle state, modifying the temperature dependence of the $3α$ rate at $T_{9} \gtrsim 2$ and ultimately, the predicted nucleosynthesis in explosive stars.
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