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Nuclear Theory·nucl-th

Thursday·June 24, 2021

7 papers—4 primary·3 cross-listed

All7Primary4Cross-lists3
  1. 01

    [Submitted on 23 Jun 2021]

    Quadrupole moments and proton-neutron structure in p-shell mirror nuclei

    M. A. Caprio · P. J. Fasano · P. Maris · A. E. McCoy

    Electric quadrupole (E2) matrix elements provide a measure of nuclear deformation and related collective structure. Ground-state quadrupole moments in particular are known to high precision in many p-shell nuclei. While the experimental electric quadrupole moment only measures the proton distribution, both proton and neutron quadrupole moments are needed to probe proton-neutron asymmetry in the nuclear deformation. We seek insight into the relation between these moments through the ab initio no-core configuration interaction (NCCI), or no-core shell model (NCSM), approach. Converged ab initio calculations for quadrupole moments are particularly challenging, due to sensitivity to long-range behavior of the wave functions. We therefore study more robustly-converged ratios of quadrupole moments: across mirror nuclides, or of proton and neutron quadrupole moments within the same nuclide. In calculations for mirror pairs in the p shell, we explore how well the predictions for mirror quadrupole moments agree with experiment and how well isospin (mirror) symmetry holds for quadrupole moments across a mirror pair.

    Comments:
    18 pages, 8 figure
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.12128 [pdf]
    PRC(2021)·17 citations
  2. 02

    [Submitted on 23 Jun 2021]

    Investigation of the nuclear liquid-gas phase transition in the static AMD

    W. Lin · P. Ren · X. Liu · H. Zheng · M. Huang · G. Qu · R. Wada

    Nuclear liquid-gas phase transitions are investigated in the framework of static antisymmetrized molecular dynamics (static AMD) model under either a constant volume or a constant pressure. A deuteron quadrupole momentum fluctuation thermometer is applied to extract the temperature of fragmenting systems of Ar and Sn. A plateau structure of caloric curves is observed under a constant volume for those system with a density 0.03 fm. A clear backbending in the caloric curves, which indicates a first order phase transition, is observed under a constant pressure with all pressures studied. The similar behavior of caloric curves of Ar and Sn systems indicates that there is no strong system size effect under a constant volume or a constant pressure. Both the mass distributions and the light particle multiplicities show a strong clusterization at low excitation energies in the static AMD simulations. The liquid-gas phase transition measures of the multiplicity derivative (dM/dT) and the normalized variance of (NVZ) are applied. The experimental caloric curves are also compared with those of Sn of the static AMD simulations under both the constant volume and the constant pressure conditions. Discussions are presented with the available experimental results and those from the static AMD simulations. Large errors in the experimental temperature measurements and those in the reconstruction technique for the primary fragmenting source hinder to draw a conclusion whether the phase transition occurs under either a constant volume or a constant pressure. This study suggests that different measures for the liquid-gas phase transitions should be examined besides the caloric curves in order to draw a conclusion.

    Comments:
    10 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.12129 [pdf]
    J.Phys.G(2021)·2 citations
  3. 03

    [Submitted on 23 Jun 2021]

    Light hyperclusters and hyperons in low-density hot stellar matter

    Tiago Custódio🇵🇹 · Helena Pais🇵🇹 · Constança Providência🇵🇹

    The abundance of light nuclei and hyperons, that are produced in stellar environments such as supernova or binary mergers, is calculated within a relativistic mean-field model with density dependent couplings in low-density matter. Five light nuclei are considered, together with three light hyper-nuclei. We show that the presence of hyperons shifts the dissolution of clusters to larger densities, and increases the amount of clusters. This effect is larger the smaller the charge fraction, and the higher the temperature. The abundance of hyperons is also affected by the cluster formation: neutral and positively charged hyperons suffer a reduction, and the negatively charged ones an increase. We also observe that the dissolution of the less-abundant clusters occurs at larger densities due to smaller Pauli-blocking effects. Overall, hyper-nuclei set in at temperatures above 25 MeV, and depending on the temperature and chemical composition, they may be more abundant than -particles, or even more abundant than other heavier clusters.

    Comments:
    12 pages, 8 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    2106.12245 [pdf]
    PRC(2021)·6 citations
  4. 04

    [Submitted on 23 Jun 2021]

    Comparison of Heavy-Ion Transport Simulations: Mean-field Dynamics in a Box

    Maria Colonna🇮🇹 · Ying-Xun Zhang🇨🇳 · Yong-Jia Wang🇨🇳 · Dan Cozma🇷🇴 · Pawel Danielewicz🇺🇸 · Che Ming Ko🇺🇸 · Akira Ono🇯🇵 · Manyee Betty Tsang🇺🇸 · Rui Wang🇨🇳 · Hermann Wolter🇩🇪 · Jun Xu🇨🇳 · Zhen Zhang and 17 other authors

    Within the transport model evaluation project (TMEP) of simulations for heavy-ion collisions, the mean-field response is examined here. Specifically, zero-sound propagation is considered for neutron-proton symmetric matter enclosed in a periodic box, at zero temperature and around normal density. The results of several transport codes belonging to two families (BUU-like and QMD-like) are compared among each other and to exact calculations. For BUU-like codes, employing the test particle method, the results depend on the combination of the number of test particles and the spread of the profile functions that weight integration over space. These parameters can be properly adapted to give a good reproduction of the analytical zero-sound features. QMD-like codes, using molecular dynamics methods, are characterized by large damping effects, attributable to the fluctuations inherent in their phase-space representation. Moreover, for a given nuclear effective interaction, they generally lead to slower density oscillations, as compared to BUU-like codes. The latter problem is mitigated in the more recent lattice formulation of some of the QMD codes. The significance of these results for the description of real heavy-ion collisions is discussed.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.12287 [pdf]
    PRC(2021)·87 citations

Affiliations

first authorsco-authorsvia INSPIRE