Charge radius of the short-lived $^{68}$Ni and correlation with the dipole polarizability
S. Kaufmann, J. Simonis, S. Bacca, J. Billowes, M. L. Bissell, K. Blaum, B. Cheal, R. F. Garcia Ruiz, W. Gins, C. Gorges, G. Hagen, H. Heylen, A. Kanellakopoulo… 展开作者
S. Kaufmann, J. Simonis, S. Bacca, J. Billowes, M. L. Bissell, K. Blaum, B. Cheal, R. F. Garcia Ruiz, W. Gins, C. Gorges, G. Hagen, H. Heylen, A. Kanellakopoulos, S. Malbrunot-Ettenauer, M. Miorelli, R. Neugart, G. Neyens, W. Nörtershäuser, R. Sánchez, S. Sailer, A. Schwenk, T. Ratajczyk, L. V. Rodríguez, L. Wehner, C. Wraith, L. Xie, Z. Y. Xu, X. F. Yang, D. T. Yordanov
We present the first laser spectroscopic measurement of the neutron-rich nucleus $^{68}$Ni at the \mbox{$N=40$} subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability $α_{\rm D}$ has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two- and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus $^{48}$Ca. Three-particle--three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of $^{68}$Ni.
We review the Lorentz integral transform coupled-cluster method for the calculation of the electric dipole polarizability. We benchmark our results with exact hyperspherical harmonics calculations for 4He and then we move to a heavier nucleus studying 16O. We observe that the implemented chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order underestimates the electric dipole polarizability.
Insights into the equation of state of neutron rich matter obtained from the neutron skin thickness of 208Pb are in sharp conflict with earlier measurements of the electric dipole polarizability. We use a set of accurately calibrated energy density functionals to highlight the tension and to articulate how plans for a highly-intense Gamma Factory may alleviate the tension.
The recent announcement by the PREX collaboration of an unanticipated thick neutron skin in 208Pb (Rskin208) has challenged our understanding of neutron rich matter in the vicinity of nuclear saturation density. Whereas earlier constraints indicate that the symmetry energy is relatively soft, the PREX-2 result seems to suggest the opposite. We confront constraints on the symmetry energy obtained from measurements of the electric dipole polarizability against those informed by the PREX-2 measurement of Rskin208 and by the correlations that it entails. Covariant energy density functionals inform…
The second random-phase-approximation model corrected by a subtraction procedure designed to cure double counting, instabilities, and ultraviolet divergences, is employed for the first time to analyze the dipole strength and polarizability in $^{48}$Ca. All the terms of the residual interaction are included, leading to a fully self-consistent scheme. Results are illustrated with two Skyrme parametrizations, SGII and SLy4. Those obtained with the SGII interaction are particularly satisfactory. In this case, the low-lying strength below the neutron threshold is extremely well reproduced and the …
The electric dipole strength distribution in Ca-48 between 5 and 25 MeV has been determined at RCNP, Osaka, from proton inelastic scattering experiments at forward angles. Combined with photoabsorption data at higher excitation energy, this enables for the first time the extraction of the electric dipole polarizability alpha_D(Ca-48) = 2.07(22) fm^3. Remarkably, the dipole response of Ca-48 is found to be very similar to that of Ca-40, consistent with a small neutron skin in Ca-48. The experimental results are in good agreement with ab initio calculations based on chiral effective field theory…
The electric dipole strength distribution in 120Sn between 5 and 22 MeV has been determined at RCNP Osaka from a polarization transfer analysis of proton inelastic scattering at E_0 = 295 MeV and forward angles including 0°. Combined with photoabsorption data an electric dipole polarizability α_D(120Sn) = 8.93(36) fm^3 is extracted. The dipole polarizability as isovector observable par excellence carries direct information on the nuclear symmetry energy and its density dependence. The correlation of the new value with the well established α_D(208Pb) serves as a test of its prediction by nuclea…
The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124 was extracted from inelastic proton scattering experiments at 295 MeV under very forward angles performed at RCNP. Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections.
Motivated by a recent experiment, the distribution of electric dipole strength in the neutron-rich 68Ni isotope was computed using a relativistic random phase approximation with a set of effective interactions that - although well calibrated - predict significantly different values for the neutron-skin thickness in 208Pb. The emergence of low-energy "Pygmy" strength that exhausts about 5-8% of the energy weighted sum rule (EWSR) is clearly identified. In addition to the EWSR, special emphasis is placed on the dipole polarizability. In particular, our results suggest a strong correlation betwee…
Revisiting neutron-skin thickness and dipole polarizability constraints on the symmetry energy in Antisymmetrized Molecular Dynamics
China Institute of Atomic Energy（中国原子能科学研究院）；Tohoku University（东北大学）；Guangxi Normal University（广西师范大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）
Electric dipole polarizability constraints on neutron skin and symmetry energy
Technische Universität Darmstadt（达姆施塔特工业大学）；Norwegian Nuclear Research Center and Department of Physics, University of Oslo（奥斯陆大学核研究中心与物理系）；Research Center for Nuclear Physics, University of Osaka（大阪大学核物理研究中心）
本文通过实验研究核的电偶极极化度及其与中子皮肤厚度和中子富集物质方程 of state 的关系，利用相对论库仑激发技术，探讨中子皮肤和对称能量密度依赖性的约束。
The recent high-resolution measurement of the electric dipole (E1) polarizability (alphad) in 208Pb [Phys. Rev. Lett. 107, 062502 (2011)] provides a unique constraint on the neutron-skin thickness of this nucleus. The neutron-skin thickness (rskin) of 208Pb is a quantity of critical importance for our understanding of a variety of nuclear and astrophysical phenomena. To assess the model dependence of the correlation between alphad and rskin, we carry out systematic calculations for 208Pb, 132Sn, and 48Ca based on the nuclear density functional theory (DFT) using both non-relativistic and relat…
Constraining the nuclear symmetry energy with electric dipole polarizability and neutron skin characteristics in \texorpdfstring{$^{208}\mathrm{Pb}$}{208Pb} within antisymmetrized molecular dynamics
China Institute of Atomic Energy（中国原子能科学研究院）；Department of Physics, Graduate School of Science, Tohoku University（东北大学理学研究科物理学系）；Guangxi Key Laboratory of Nuclear Physics and Technology, Guangxi Normal University（广西师范大学核物理与技术重点实验室）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心）
Nuclear structure observables usually most effectively probe the properties of nuclear matter at subsaturation densities rather than at saturation density. We demonstrate that the electric dipole polarizibility $α_ {\text{D}}$ in $^{208}$Pb is sensitive to both the magnitude $E_{\text{sym}}(ρ_{\text{c}})$ and density slope $L(ρ_{\text{c}})$ of the symmetry energy at a subsaturation cross density $ρ_{\text{c}} = 0.11$ fm$^{-3}$. Using the experimental data of $α_ {\text{D}}$ in $^{208}$Pb from RCNP and the recent accurate constraint of $E_{\text{sym}}(ρ_{\text{c}})$ from the binding energy diff…
We present an estimate of the nuclear electric polarizability of the 6He halo nucleus based on six-body microscopic calculations. Wave functions are obtained from semi-realistic two-body interactions using the hyperspherical harmonics expansion method. The polarizability is calculated as a sum rule of the dipole response function using the Lanczos algorithm and also by integrating the photo-absorption cross section calculated via the Lorentz integral transform method. We obtain alpha_E=1.00(14) fm^3, which is much smaller than the published value 1.99(40) fm^3 extracted from experimental data.…
It is currently a big challenge to accurately determine the symmetry energy $E_{\text{sym}}(ρ)$ and the pure neutron matter equation of state $E_{\text{PNM}}(ρ)$, even their values around saturation density $ρ_0 $. We find that the electric dipole polarizability $α_ {\text{D}}$ in $^{208}$Pb can be determined uniquely by the magnitude of the $E_{\text{sym}}(ρ)$ or almost equivalently the $E_{\text{PNM}}(ρ)$ at subsaturation densities around $ρ_0/3 $, shedding a light upon the genuine correlation between the $α_ {\text{D}}$ and the $E_{\text{sym}}(ρ)$. By analyzing the experimental data of the …
Nuclear collective motion provides valuable constraint on the size of neutron-skin thickness and the properties of nuclear matter symmetry energy. By employing relativistic nuclear energy density functional (RNEDF) and covariance analysis related to $χ^2$ fitting of the model parameters, relevant observables are identified for dipole excitations, which strongly correlate with the neutron-skin thickness $(r_{np})$, symmetry energy at saturation density $(J)$ and slope of the symmetry energy $(L)$. Using the RNEDF framework and experimental data on pygmy dipole strength ($^{68}$Ni, $^{132}$Sn, $…
We probe nuclear multipole resonances in the framework of the random-phase approximation by using the interaction obtained from the chiral effective field theory. The three-nucleon force is included in a form of the in-medium two-nucleon interaction which was derived from the chiral three-nucleon force. The isoscalar monopole, isoscalar dipole, isovector dipole and isoscalar quadrupole resonances of the closed-shell $^{56,68,78}$Ni have been investigated. The calculations reasonably reproduce the experimental multipole resonances of $^{56,68}$Ni, and well describe the pygmy dipole resonance an…
We have studied the isoscalar giant quadruple resonance (ISGQR) and the isovector giant dipole resonance (IVGDR) in $^{208}$Pb based on an improved isospin-dependent Boltzmann-Uehling-Uhlenbeck transport approach using an improved isospin- and momentum-dependent interaction. With the isoscalar nucleon effective mass and the nucleon-nucleon cross section which reproduces respectively the excitation energy and the width of the ISGQR strength function, the slope parameter of the symmetry energy and the neutron-proton effective mass splitting are constrained respectively within $36<L<62$ MeV and $…
I extend the well-known photonuclear sum rule that relates the strength of the photoexcitation of the giant dipole resonance in a nucleus to the number of elementary scatterers-nucleons to the case of virtual photons. The new sum rule relates the size of the magnetic polarizability of a nucleus to the slope of the transverse virtual photoabsorption cross section integrated over the energy in the nuclear range. I check this sum rule for the deuteron where necessary data is available, discuss possible applications and connection with other sum rules postulated in the literature.
