Hindrance of the excitation of the Hoyle state and the ghost of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msubsup><mml:mn>2</mml:mn><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math> state in 12C

Khoa, Dao T.; Cuong, Do Cong; Kanada-En’yo, Yoshiko

doi:10.1016/j.physletb.2010.11.061

Cited by 18 publications

(13 citation statements)

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“…These rates, in turn, are greatly influenced by accurate measurements and theoretical predictions of several important low-lying states in 12 C, including the second 0 + 2 (Hoyle) state and its 2 + excitation that has fostered long-lasting debate in experimental studies [114][115][116][117][118][119][120]. Further challenges relate to the α-cluster substructure of these states that has been explored within clustertailored [121][122][123][124][125][126] or self-consistent [127,128] framework, but has hitherto precluded a fully microscopic ab initio no-core shell-model description [129] (see, e.g., detailed reviews on the topic [130,131]). Only recently, first ab initio state-of-the-art calculations have been attempted using lattice effective field theory (EFT) [17,132].…”

Section: No-core Symplectic Shell Model (Ncspm) and The Elusive Hoylementioning

confidence: 99%

Symmetry-guided large-scale shell-model theory

Launey

Dytrych

Draayer

2016

Progress in Particle and Nuclear Physics

125

173

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In this review, we present a symmetry-guided strategy that utilizes exact as well as partial symmetries for enabling a deeper understanding of and advancing ab initio studies for determining the microscopic structure of atomic nuclei. These symmetries expose physically relevant degrees of freedom that, for large-scale calculations with QCD-inspired interactions, allow the model space size to be reduced through a very structured selection of the basis states to physically relevant subspaces. This can guide explorations of simple patterns in nuclei and how they emerge from first principles, as well as extensions of the theory beyond current limitations toward heavier nuclei and larger model spaces. This is illustrated for the ab initio symmetry-adapted no-core shell model (SA-NCSM) and two significant underlying symmetries, the symplectic Sp(3, R) group and its deformation-related SU(3) subgroup. We review the broad scope of nuclei, where these symmetries have been found to play a key role -from the light p-shell systems, such as 6 Li, 8 B, 8 Be, 12 C, and 16 O, and sd-shell nuclei exemplified by 20 Ne, based on first-principle explorations; through the Hoyle state in 12 C and enhanced collectivity in intermediate-mass nuclei, within a no-core shell-model perspective; up to strongly deformed species of the rare-earth and actinide regions, as investigated in earlier studies. A complementary picture, driven by symmetries dual to Sp(3, R), is also discussed. We briefly review symmetry-guided techniques that prove useful in various nuclear-theory models, such as Elliott model, ab initio SA-NCSM, symplectic model, pseudo-SU(3) and pseudo-symplectic models, ab initio hyperspherical harmonics method, ab initio lattice effective field theory, exact pairing -plusshell model approaches, and cluster models, including the resonating-group method. Important implications of these approaches that have deepened our understanding of emergent phenomena in nuclei, such as enhanced collectivity, giant resonances, pairing, halo, and clustering, are discussed, with a focus on emergent patterns in the framework of the ab initio SA-NCSM with no a priori assumptions.

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Section: No-core Symplectic Shell Model (Ncspm) and The Elusive Hoylementioning

confidence: 99%

Symmetry-guided large-scale shell-model theory

Launey

Dytrych

Draayer

2016

Progress in Particle and Nuclear Physics

125

173

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“…With the complex strength of the density dependent nucleon-nucleon interaction fixed by the optical model description of the elastic α+ 12 C scattering, the inelastic scattering form factor was fine tuned to the best coupled-channel description of the (α, α ) cross section measured for each excited state of 12 C, and the corresponding isoscalar Eλ transition strength has been accurately determined. The present analysis of the (α, α ) data measured in the energy bins around E x ≈ 10 MeV has unambiguously revealed the E2 transition strength that should be assigned to the 2 The synthesis of 12 C during the helium burning process is known to proceed through the triple-α reaction, where an unstable 8 Be formed by the fusion of two α-particles captures the third α-particle to form 12 C in the 0 + excited state at 7.65 MeV, which decays to the ground state via γ emission. This monopole excitation of 12 C (named as Hoyle state) has been first predicted by Fred Hoyle [1] in 1953, and observed later in the deuteron pickup reaction 14 N(d, α) 12 C * (E x = 7.653 MeV) [2].…”

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confidence: 58%

“…Besides its unique role in the carbon synthesis, the Hoyle state is also famous as having a pronounced three α-cluster structure. Given a nonspherical shape of the 8 Be + α configuration, an excited rotational band with the angular momentum J π = 2 + , 4 + , ... built upon the Hoyle state was suggested long ago by Morinaga [4]. The second 2 + state of 12 C was also predicted by the different structure models like the Resonating Group Method [5,6] or the antisymmetrized molecular dynamics (AMD) [7,8] at the excitation energy around 10 MeV, about 2 MeV above the α threshold.…”

mentioning

confidence: 99%

“…Given a nonspherical shape of the 8 Be + α configuration, an excited rotational band with the angular momentum J π = 2 + , 4 + , ... built upon the Hoyle state was suggested long ago by Morinaga [4]. The second 2 + state of 12 C was also predicted by the different structure models like the Resonating Group Method [5,6] or the antisymmetrized molecular dynamics (AMD) [7,8] at the excitation energy around 10 MeV, about 2 MeV above the α threshold. Because of the pronounced α-cluster structure predicted for the 2 + 2 state of 12 C, many experimental studies were aimed to observe it in the spectra of the different reactions involving 12 C (see the recent review [3]).…”

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confidence: 99%

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The 2⁺excitation of the Hoyle state

Khoa

Cuong

Kanada-En’yo³

2016

EPJ Web of Conferences

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Abstract. To understand why the 2 + excitation of the Hoyle state was so difficult to observe in the direct reaction experiments with the 12 C target, a detailed folding model + coupled-channel analysis of the inelastic α+ 12 C scattering at E lab = 240 and 386 MeV has been done using the complex optical potential and inelastic scattering form factor obtained from the double-folding model using the nuclear transition densities predicted by the antisymmetrized molecular dynamics. With the complex strength of the density dependent nucleon-nucleon interaction fixed by the optical model description of the elastic α+ 12 C scattering, the inelastic scattering form factor was fine tuned to the best coupled-channel description of the (α, α ) cross section measured for each excited state of 12 C, and the corresponding isoscalar Eλ transition strength has been accurately determined. The present analysis of the (α, α ) data measured in the energy bins around E x ≈ 10 MeV has unambiguously revealed the E2 transition strength that should be assigned to the 2 + 2 state of 12 C. A very weak transition strength B(E2; 02 fm 4 has been established, which is smaller than the E2 strength predicted for the transition from the Hoyle state to the 2 + 2 state by at least two orders of magnitude. This is one of the main reasons why the direct excitation of the 2 + 2 state of 12 C has been difficult to observe in the experiments.

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“…However, a recent experiment performed in this line [10], where complete kinematical measurement of all outgoing particles emitted from the reactions 10 2 2 + state. Since the spin and isospin zero α-particle is a very good projectile for the excitation of the nuclear IS states [9], we studied the decay of 12 C * into 3-body final states (3α) using inelastic α scattering from 12 C target to study the excited states of 12 C which are predominantly excitable through isoscalar transitions in general, and to look for a cleaner signature of the elusive 2 2 + state in particular. The present study clearly demonstrates the presence of an excited state of 12 C at excitation energy of 9.65 ± 0.02 MeV energy and width (FWHM) 607 ± 55 keV, which is decaying via the 0 2 + Hoyle state, most likely the excited state of Hoyle state.…”

Section: Introductionmentioning

confidence: 99%