Neutron Skin Research Articles

Neutron skins: A perspective from dispersive optical models

An overview of neutron skin predictions obtained using an empirical nonlocal dispersive optical model (DOM) is presented. The DOM links both scattering and bound-state experimental data through a subtracted dispersion relation which allows for fully consistent, data-informed predictions for nuclei where such data exist. Large skins were predicted for both 48Ca (Rskin48=0.25±0.023 fm in 2017) and 208Pb (Rskin208=0.25±0.05 fm in 2020). Whereas the DOM prediction in 208Pb is within 1σ of the subsequent PREX-2 measurement, the DOM prediction in 48Ca is over 2σ larger than the thin neutron skin resulting from CREX. From the moment it was revealed, the thin skin in 48Ca has puzzled the nuclear-physics community as no adequate theories simultaneously predict both a large skin in 208Pb and a small skin in 48Ca. The DOM is unique in its ability to treat both structure and reaction data on the same footing, providing a unique perspective on this Rskin puzzle. It appears vital that more neutron data be measured in both the scattering and bound-state domain for 48Ca to clarify the situation.

New quantification of symmetry energy from neutron skin thicknesses of 48Ca and 208Pb

New quantification of symmetry energy from neutron skin thicknesses of 48Ca and 208Pb

A Study of the Neutron Skin of Nuclei with Dileptons in Nuclear Collisions

A Study of the Neutron Skin of Nuclei with Dileptons in Nuclear Collisions

Exploring the Diversity of Nuclear Density through Information Entropy.

This study explores the role of information entropy in understanding nuclear density distributions, including both stable configurations and non-traditional structures such as neutron halos and α-clustering. By quantifying the uncertainty and disorder inherent in nucleon distributions in nuclear many-body systems, information entropy provides a macroscopic measure of the physical properties of the system. A more dispersed and disordered density distribution results in a higher value of information entropy. This intrinsic relationship between information entropy and system complexity allows us to quantify uncertainty and disorder in nuclear structures by analyzing various geometric parameters such as nuclear radius, diffuseness, neutron skin, and cluster structural features.

Hard probes in isobar collisions as a probe of the neutron skin

We present an estimate of the yield of hard probes expected for collisions of the isobars 4496Ru and 4096Zr at collision energies reachable at RHIC and the LHC. These yields are proportional to the number of binary nucleon-nucleon interactions, which is characteristically different due to the presence of the large neutron skin in 4096Zr. This provides an independent opportunity to measure the difference between the neutron skin of 4496Ru and 4096Zr, which can provide an important constraint on the Equation of State of cold neutron-rich matter.

Neutron Skins: Weak Elastic Scattering and Neutron Stars

The recently completed PREX-2 campaign measured the density distribution of neutrons in the lead nucleus as a function of momentum transfer (the form factor), confirmed a relatively large extent of the neutrons beyond the protons in the nucleus (the neutron skin), and provided a precise determination of the density of protons and neutrons at the center of a heavy nucleus. In turn, the measured form factor can be related to various nuclear and neutron star properties. The NICER X-ray telescope has inferred the masses and radii of some X-ray pulsars (neutron stars), although complications arise when determining these quantities independently. Further improvements in NICER have enabled simultaneous mass–radius determinations that had not previously been possible. During the next decade, measurements in astrophysics, gravitational-wave astronomy, and nuclear physics are expected to provide a wealth of more precise data. In this review, we present an overview of the current state of neutron skin measurements and offer insights into prospects for the future.

Relativistic description of dense matter equation of state and neutron star observables constrained by recent astrophysical observations

In the present work, we investigate the bulk properties of nuclear matter and neutron stars with the newly proposed relativistic interaction NL-RS which provides an opportunity to readjust the coupling constants keeping in view the properties of finite nuclei, nuclear matter, PREX-II results for neutron skin thickness in 208Pb and astrophysical observations. The NL-RS model interaction has been proposed by fitting the ground state properties (binding energies and charge radii) of finite nuclei, bulk nuclear matter properties, and PREX-II results for neutron skin thickness of 208Pb. The relativistic interaction has been generated by including nonlinear self-interactions of σ and ω μ -mesons and mixed interactions of ω μ , and ρ μ -meson up to the quartic order. The proposed interaction harmonizes with the finite nuclei, bulk nuclear matter, and neutron star properties. A covariance analysis is performed to assess the statistical uncertainties on the model parameters and nuclear observables of interest along with correlations amongst them. The equation of state (EoS) composed of nucleons and leptons in β-equilibrium is computed with the proposed parameter set and used to study the neutron star structure. The maximum mass of the neutron star by employing the EoS computed with the NL-RS parameter set is 2.04 ± 0.03M ⊙ and the radius of a canonical mass neutron star (R 1.4) comes out to be equal to 13.06 ± 0.16 Km. The value of dimensionless tidal deformability, for canonical mass, is 602.23 ± 33.13 which satisfies the constraints of waveform models analysis of GW170817 within 90% confidence level.

Structural and decay properties of even–even trans-lead nuclei

A systematic study of the ground-state properties of even–even Po, Rn, Ra and Th isotopes is conducted using the self-consistent Skyrme-Hartree–Fock–Bogoliubov (HFB) theory. Different Skyrme interactions are employed in the study. The bulk properties such as binding energy, two-neutron separation energies, two-proton separation energies and neutron skin thickness are investigated. The obtained results from the Skyrme-HFB formalism are compared with the calculated results from the Finite Range Droplet Model (FRDM) and the available experimental data. Our theoretical values were found to be consistent with their counterparts. In addition, the density-dependent cluster model is utilized to estimate [Formula: see text]-decay half-lives. A good agreement is achieved between the calculated results and the recent experimental data.

Hybrid Star Models in the Light of New Multimessenger Data

Recent astrophysical mass inferences of compact stars HESS J1731-347 and PSR J0952-0607, with extremely small and large masses respectively, as well as the measurement of the neutron skin of Ca in the CREX experiment challenge and constrain the models of dense matter. We examine the concept of hybrid stars—objects containing quark cores surrounded by nucleonic envelopes—as models that account for these new data along with other inferences. We employ a family of 81 nucleonic equations of state (EOSs) with variable skewness and slope of symmetry energy at saturation density and a constant speed-of-sound EOS for quark matter. For each nucleonic EOS, a family of hybrid EOSs is generated by varying the transition density, the energy jump, and the speed of sound. These models are tested against the data from GW170817 and J1731-347, which favor low-density soft EOS and J0592-0607 and J0740+6620, which require high-density stiff EOS. The addition of J0592-0607's mass measurement to the constraints has no significant impact on the parameter space of the admissible EOS, but allows us to explore the potential effect of pulsars more massive than J0740+6620, if such exists. We then examine the occurrence of twin configurations and quantify the ranges of masses and radii that they can possess. It is shown that including J1731-347 data favors EOSs that predict low-mass twins with M ≲ 1.3 M ⊙ that can be realized if the deconfinement transition density is low. If combined with large speed of sound in quark matter such models allow for maximum masses of hybrid stars in 2.0–2.6 M ⊙.

Linkage among the neutron-skin thickness of 208Pb and nuclear symmetry energy using heavy particle radioactivity

The nuclear symmetry energy (NSE) is a linchpin in deciphering the behavior of matter in a wider domain extending from the characteristics of exotic nuclei to those of neutron stars in the cosmos. Therefore, it is crucial to utilize potential probes to constrain the NSE and its slope parameter L(ρ 0). In this work, we put forth the heavy particle radioactivity (HPR) as a probable bridge among the slope of NSE (L(ρ 0)) and neutron-skin thickness of 208Pb (R skin 208), which serves to put constrain on the L(ρ 0) value. The NSE and its slope parameter are determined from the single nucleon potential of asymmetric nuclear matter exploiting the analytical relationship between these quantities. The isovector/symmetry potential component of the single nucleon potential is derived through HPR for varying R skin 208 by employing the heavy particle/cluster densities and core densities from the relativistic mean field model in conjunction with M3Y nucleon–nucleon interaction. It facilitates in constraining the L(ρ 0) value and neutron skin of finite nuclei using HPR as a linkage, where heavy cluster and core densities of standard Fermi form are considered. The constrained value of L(ρ o ) is 45 ± 8 MeV, which aligns with other estimations derived from nuclear mass measurements, dipole polarizability measurements, and astrophysical data.

A systematic study of the ground state properties of gold nuclei near the neutron drip line using HFB formalism

In this theoretical work, the ground state properties like binding energy per nucleon, two-neutron separation energy, two-neutron shell gap, neutron-pairing gap, neutron rms radii, proton rms radii, charge radii, neutron skin thickness and nucleon density distributions of odd-even and odd-odd gold isotopes (A165−265u) were systematically studied. Computations were performed for a wide mass range of gold nuclei, spanned from the proton-rich side to the neutron-rich side, following the Hartree-Fock-Bogoliubov theory. Based on this approach, the nuclear structure of gold isotopes lying up to the exotic neutron rich region where the experimental data are not available, was also investigated. Calculations, taking into account the UNEDF0 Skyrme effective interaction, reproduce the available experimental data and results of other nuclear model based estimations, such as the Relativistic-Continuum-Hartree-Bogoliubov theory and the Finite Range Droplet Models, reasonably well.

Electric dipole polarizability of magic nuclei

The correlations between the electric dipole polarizability and neutron skin thickness are studied by the magic nuclei 40,48Ca, 68,78Ni, 132Sn, and 208Pb. The strength distribution of the E1 transitions is calculated within the random phase approximation model based on the Skyrme nuclear energy density functional. A comparison with the experimental data has allowed us to constrain the value of the nuclear symmetry energy J = 30–37 MeV.

Determination of Nuclear Matter Radii by Means of Microscopic Optical Potentials: The Case of 78\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{78}$$\\end{document}Kr

In this work we use microscopic Nucleon–Nucleus Optical Potentials (OP) to analyze elastic scattering data for the differential cross section of the 78\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{78}$$\\end{document}Kr (p,p) 78\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{78}$$\\end{document}Kr reaction, with the goal of extracting the matter radius and estimating the neutron skin, quantities that are both needed to determine the slope parameter L of the nuclear symmetry energy. Our analysis is performed with the factorized version of the microscopic OP obtained in a previous series of papers within the Watson multiple scattering theory at the first order of the spectator expansion, which is based on the underlying nucleon–nucleon dynamics and is free from phenomenological inputs. Differently from our previous applications, the proton and neutron densities are described with a two-parameter Fermi (2pF) distribution, which makes the extraction of the matter radius easier and allows us to make a meaningful comparison with the original analysis, that was performed with the Glauber model. With standard minimization techniques we performed data analysis and extracted the matter radius and the neutron skin. Our analysis produces a matter radius of Rm(rms)=4.12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R_m^{\\mathrm{(rms)}} = 4.12$$\\end{document} fm, in good agreement with previous matter radii extracted from 76\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{76}$$\\end{document}Kr and 80\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{80}$$\\end{document}Kr, and a neutron skin of ΔRnp≃-0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta R_{np} \\simeq - 0.1$$\\end{document} fm, compatible with a previous analysis. Our factorized microscopic OP, supplied with 2pF densities, is a valuable tool to perform the analysis of the experimental differential cross section and extract information such as matter radius and neutron skin. Without any free parameters it provides a reasonably good description of the experimental differential cross section for scattering angles up to ≈\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\approx $$\\end{document} 40 degrees. Compared to the Glauber model our OP can be applied to a wider range of scattering angles and allows one to probe the nuclear systems in a more internal region.

Implications on Skyrme equations of state from neutron skin measurements

Abstract The recent measurements on neutron skins via parity violation in electron scattering have extracted an abnormal thick neutron skin for $^{208}$Pb, which has significant consequences in nuclear equation of state (EoS) and neutron star observations. This work performs optimizations of extended Skyrme forces in a consistent manner by including neutron skin thicknesses from PREX-II and CREX experiments
and investigates nuclear EoS and neutron stars in the GW170817 event. By varying the fitting weights of neutron skins, several new Skyrme parameterizations are obtained. Our results show the competition in the fitting procedure to simultaneously describe neutron skins, other properties of finite nuclei and neutron star observations. The prospects in resolving the neutron skin issues are also discussed.

Determining the neutron skin thickness by relativistic semi-isobaric collisions

Determining the neutron skin thickness by relativistic semi-isobaric collisions

Polaronic proton and diproton clustering in neutron-rich matter

We show that the strong spin-triplet neutron-proton interaction causes polaronic protons to occur in neutron matter at subnuclear densities and nonzero temperatures. As the neutron density increases, proton spectra exhibit a smooth crossover from a bare impurity to a repulsive polaron branch; this branch coexists with an attractive polaron branch. With the neutron density increased further, the attractive polarons become stable with respect to deuteron formation. For two adjacent protons, we find that the polaron effects and the neutron-mediated attraction are sufficient to induce a bound diproton, which leads possibly to diproton formation in the neutron skin region of neutron-rich nuclei in laboratories as well as in neutron stars.

A study of trends of neutron skin thickness and proton radii of mirror nuclei within the framework of covariant density functional theory

The neutron skin of atomic nuclei impacts the structure of neutron-rich nuclei, but its accurate measurement is quite challenging. We present predictions for neutron skins and proton radii for light to medium mass nuclei by employing Covariant Density Functional Theory (CDFT) based on density-dependent meson-exchange interaction. Using our microscopic predictions, we find a linear correlation between the neutron skin and the isospin asymmetry. The calculations are also extended to find a linear relationship between proton and neutron radii of mirror nuclei. Using the charge symmetry property of nuclear forces, a correlation between the neutron skin of neutron-rich nuclei and difference between the proton radii of the corresponding mirror pair has also been investigated. The inclusion of ISB term is found to affect the mirror difference charge radii of [Formula: see text]Ca-[Formula: see text]Ni mirror pair.

Isotopic dependence of the yield ratios of light fragments from different projectiles and their unified neutron skin thicknesses

Isotopic dependence of the yield ratios of light fragments from different projectiles and their unified neutron skin thicknesses

Neutron skin of 27Al with Skyrme and Korea-IBS-Daegu-SKKU density functionals

Recent measurement of the parity-violating (PV) asymmetry in the elastic electron scattering on [Formula: see text]Al target evokes the interest in the distribution of the neutron in the nucleus. In this work, we calculate the neutron skin thickness ([Formula: see text]) of [Formula: see text]Al with nonrelativistic nuclear structure models. We focus on the role of the effective mass, symmetry energy and pairing force. Models are selected to have effective masses in the range (0.58–1.05) M where M is the nucleon mass in free space, and stiffness of the symmetry energy is varied by choosing the slope of the symmetry energy in the range 9.4–100.5[Formula: see text]MeV. Effect of pairing force is investigated by calculating nuclear properties with and without pairing. With constant force pairing, we obtain [Formula: see text]–0.013[Formula: see text]fm. The result is independent of the effective mass and symmetry energy. However, [Formula: see text] is negative when the pairing force is switched off, so the pairing force plays an essential role to make [Formula: see text] positive and constrained in a narrow range. We also calculate the PV asymmetry ([Formula: see text]) in the elastic electron-[Formula: see text]Al scattering in the Born approximation at the kinematics of the Qweak experiment. We obtain a very narrow-ranged result [Formula: see text]. The result is consistent with the experiment and insensitive to the effective mass and symmetry energy.

Hybrid stars and the stiffness of the nuclear equation of state in light of the HESS J1731-347 remnant

The recent observation of the extremely compact neutron star in the HESS J1731-347 remnant has challenged our understanding concerning the nature of dense nuclear matter. In particular, the low radius of the aforementioned compact object favors soft nuclear equations of state. However, the neutron skin thickness of 208Pb extracted from the long-awaited PREX-II experiment favors stiff equations of state which may be associated with larger radii for low mass stellar configurations. In this contribution we present our recent work on the possible reconciliation of the HESS J1731-347 observation in the framework of hybrid stars, under the assumption of a stiff low-density phase which may be favored by the PREX-II results. In addition, we examine the compatibility of the resulting hybrid models with recent constraints based on the observation of PSR J0030+0451, PSR J0952-0607 and GW190814.