Background: The possibility that an unconventional depletion (referred to as a "bubble") occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which Si34 appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable Si34 is currently out of reach, (d,p) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1/2 - 3/2- splitting in the spectrum of Si35 as compared to S37. Purpose: We study the potential bubble structure of Si34 on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of Si34 and S36. In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in S36. The next observable of interest is the low-lying spectroscopy of Si35 and S37 obtained from (d,p) experiments along with the spectroscopy of Al33 and P35 obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in Si34 varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of S36 be well reproduced, along with Si34 and S36 binding energies, only leaves the NNLOsat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of Si34, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2 - 3/2- splitting in the spectrum of Si35 as compared to S37. Conclusions: The occurrence of a bubble structure in the charge distribution of Si34 is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of Si34 in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on Si34 and S36 in order to further test our theoretical spectral strength distributions over a wide energy range.

Ab initio calculation of the potential bubble nucleus Si 34 / T. Duguet, V. Soma, S. Lecluse, C. Barbieri, P. Navratil. - In: PHYSICAL REVIEW C. - ISSN 2469-9985. - 95:3(2017), pp. 034319.1-034319.17. [10.1103/PhysRevC.95.034319]

Ab initio calculation of the potential bubble nucleus Si 34

C. Barbieri;
2017

Abstract

Background: The possibility that an unconventional depletion (referred to as a "bubble") occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which Si34 appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable Si34 is currently out of reach, (d,p) experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak 1/2 - 3/2- splitting in the spectrum of Si35 as compared to S37. Purpose: We study the potential bubble structure of Si34 on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method. Methods: We perform the first ab initio calculations of Si34 and S36. In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in S36. The next observable of interest is the low-lying spectroscopy of Si35 and S37 obtained from (d,p) experiments along with the spectroscopy of Al33 and P35 obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in Si34 varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of S36 be well reproduced, along with Si34 and S36 binding energies, only leaves the NNLOsat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of Si34, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2 - 3/2- splitting in the spectrum of Si35 as compared to S37. Conclusions: The occurrence of a bubble structure in the charge distribution of Si34 is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of Si34 in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on Si34 and S36 in order to further test our theoretical spectral strength distributions over a wide energy range.
greens-function; numbers; mass
Settore FIS/04 - Fisica Nucleare e Subnucleare
2017
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/709822
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