Three-body effects in the Hoyle-state decay

Abstract

We use a sequential R-matrix model to describe the breakup of the Hoyle state into three α particles via the ground state of 8 Be. It is shown that even in a sequential picture, features resembling a direct breakup branch appear in the phase-space distribution of the α particles. We construct a toy model to describe the Coulomb interaction in the three-body final state and its effects on the decay spectrum are investigated. The framework is also used to predict the phase-space distribution of the α particles emitted in a direct breakup of the Hoyle state and the possibility of interference between a direct and sequential branch is discussed. Our numerical results are compared to the current upper limit on the direct decay branch determined in recent experiments.

The Hoyle Family: The Search for Alpha-Condensate States in Light Nuclei

“…This model accounts for the changing 3α decay penetrability depending on the relative energies and directions of the α-particles as they tunnel from the nucleus. Its similarity in results to an R-matrix model of the direct decay have previously been noted [49]. In this model, it is calculated that the Coulomb barrier for an equal energies DDE decay is significantly lower than for a collinear DDL decay.…”

“…However, in their paper, they only consider DDE-type decays because "We expect a change less than a factor of 2 [by] adding more configurations". In contrast to this, the 3α phase space distributions calculated in references [49] and [51] demonstrate a large dependence of the barrier transmission probability on the relative energies/orientations of the three α-particles. Furthermore, the Coulomb interaction chosen by Zheng et al was modified to reflect the potential energy of two overlapping, uniformly charged spheres, parameterised for a 2-body decay as…”

The Hoyle Family: break-up measurements to probe α-condensation in light nuclei

“…This model accounts for the changing 3α decay penetrability depending on the relative energies and directions of the α-particles as they tunnel from the nucleus. Its similarity in results to an R-matrix model of the direct decay have previously been noted [29]. In this model, it is calculated that the Coulomb barrier for an equal energies DDE decay is significantly lower than for a collinear DDL decay.…”

“…However, in their paper, they only consider DDE-type decays because "We expect a change less than a factor of 2 [by] adding more configurations". In contrast to this, the 3α phase space distributions calculated in references [29] and [28] demonstrate a large dependence of the barrier transmission probability on the relative energies/orientations of the three α-particles. Furthermore, the Coulomb interaction chosen by Zheng et al was modified to reflect the potential energy of two overlapping, uniformly charged spheres, parameterised for a 2-body decay as…”

Stringent upper limit on the direct 3α decay of the Hoyle state in C12

“…These rare "direct decay" events have previously been identified [25] as the combined sequential 12 C(γ, α 1 ) 8 Be 2 + and direct 12 C(γ, 3α) dissociation of the 10 MeV second 2 + state of 12 C. The two have strongly overlapping kinematics because the 8 Be 2 + is so broad [Γ ≈ 1.5 MeV]. As highlighted in a recent theoretical study [26], decays through the broad 8 Be g.s. ghost anomaly are also indistinguishable from direct 3α decays.…”