Investigating the predicted breathing-mode excitation of the Hoyle state

Abstract

Knowledge of the low-lying monopole strength in ${}^{12}\mathrm{C}$ $-$ the Hoyle state in particular $-$ is crucial for our understanding of both the astrophysically important $3\alpha$ reaction and of $\alpha$-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 $\alpha$ clusters. The ${}^{12}\mathrm{C}(\alpha ,{\alpha }^{\prime }){}^{12}\mathrm{C}$ and ${}^{14}\mathrm{C}(p,t){}^{12}\mathrm{C}$ 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 $3\alpha$ rate at $T_9\gtrsim 2$ and ultimately, the predicted nucleosynthesis in explosive stars.

8 pages, 5 figures

References in corpus (7)

• Structure and rotations of the Hoyle state
• Evidence for Triangular D_3h Symmetry in 12C
• High precision probe of the fully sequential decay width of the Hoyle state in ${}^{12}$C
• Breathing-like excited state of the Hoyle state in ${}^{12}\mathrm{C}$
• A stringent upper limit on the direct 3$\alpha$ decay of the Hoyle State in ${}^{12}$C
• Almost medium-free measurement of the Hoyle state direct-decay component with a TPC
• CAKE: The Coincidence Array for K600 Experiments

Cited by in corpus (5)

• Emergent geometry and duality in the carbon nucleus
• Cluster structures of the $0^{+}$ states of ${}_{\Lambda }^{13}\mathrm{C}$ with the 3$\alpha +\Lambda$ four-body orthogonality condition model
• Understanding the total width of the $3_1^{-}$ state in ${}^{12}\mathrm{C}$
• Low-energy ${}^{12}$C continuum states in three-$\alpha$ model
• Examination of the $\alpha$-cluster breaking in the four $0^{+}$ bands of ${}^{12}$C with the variation of multiple bases of the antisymmetrized molecular dynamics