Nuclear Theory·nucl-th

Wednesday·November 11, 2020

8 papers—6 primary·2 cross-listed

01
Discerning nuclear pairing properties from magnetic dipole excitation
Tomohiro Oishi · Goran Kruzic · Nils Paar
Pairing correlation of Cooper pair is a fundamental property of multi-fermion interacting systems. For nucleons, two modes of the Cooper-pair coupling may exist, namely of $S_{12} = 0$ with $L_{12} = 0$ (spin-singlet s-wave) and $S_{12} = 1$ with $L_{12} = 1$ (spin-triplet p-wave). In nuclear physics, it has been an open question whether the spin-singlet or spin-triplet coupling is dominant, as well as how to measure their role. We investigate a relation between the magnetic-dipole (M1) excitation of nuclei and the pairing modes within the framework of relativistic nuclear energy-density functional (RNEDF). The pairing correlations are taken into account by the relativistic Hartree-Bogoliubov (RHB) model in the ground state, and the relativistic quasi-particle random-phase approximation (RQRPA) is employed to describe M1 transitions. We have shown that M1 excitation properties display a sensitivity on the pairing model involved in the calculations. The systematic evaluation of M1 transitions together with the accurate experimental data enables us to discern the pairing properties in finite nuclei.
nucl-thcond-mat.supr-connucl-exEPJA(2021)·7 citations
02
Three-body structure of $^{19}$ B: Finite-range effects in two-neutron halo nuclei
J. Casal · E. Garrido
The structure and $B (E 1)$ transition strength of $^{19}$ B are investigated in a $^{17} B + n + n$ model, triggered by a recent experiment showing that $^{19}$ B exhibits a well pronounced two-neutron halo structure. Preliminary analysis of the experimental data was performed by employing contact $n$ - $n$ interactions, which are known to underestimate the $s$ -wave content in other halo nuclei such as $^{11}$ Li. In the present work, the three-body hyperspherical formalism with finite-range two-body interactions is used to describe $^{19}$ B. In particular, two different finite-range $n$ - $n$ interactions will be used, as well as a simple central Gaussian potential whose range is progressively reduced. The purpose is to determine the main properties of the nucleus and investigate how they change when using contact-like $n$ - $n$ potentials. Special attention is also paid to the dependence on the prescription used to account for three-body effects, i.e., a three-body force or a density-dependent $n$ - $n$ potential. We have found that the three-body model plus finite-range potentials provide a description of $^{19}$ B consistent with the experimental data. The results are essentially independent of the short-distance details of the two-body potentials, giving rise to an $(s_{1/2})^{2}$ content of about 55%, clearly larger than the initial estimates. Very little dependence has been found as well on the prescription used for the three-body effects. The total computed $B (E 1)$ strength is compatible with the experimental result, although we slightly overestimate the data around the low-energy peak of the $d B (E 1) / d ε$ distribution. Finally, we show that a reduction of the $n$ - $n$ interaction range produces a significant reduction of the $s$ -wave contribution, which then should be expected in calculations using contact interactions.
nucl-thnucl-exPRC(2020)·15 citations
03
Pseudorapidity distributions of charged particles in pp( $p$ ), p(d)A and AA collisions using Tsallis thermodynamics
J.Q. Tao🇨🇳 · M. Wang🇨🇳 · H. Zheng🇨🇳 · W.C. Zhang🇨🇳 · L.L. Zhu🇨🇳 · A. Bonasera🇺🇸
The pseudorapidity distributions of charged particles measured in p+p( $p$ ) collisions for energies ranging from $s_{N N} = 23.6$ GeV to 13 TeV, d+Au collisions at $s_{N N} = 200$ GeV, p+Pb collisions at $s_{N N} = 5.02$ TeV and A+A collisions at RHIC and LHC are investigated in the fireball model with Tsallis thermodynamics. We assume that the rapidity axis is populated with fireballs following q-Gaussian distribution and the charged particles follow the Tsallis distribution in the fireball. The theoretical results are in good agreement with the experimental data for all the collision systems and centralities investigated. The collision energy and centrality dependence of the central position $y_{0}$ and its width $σ$ of the fireball distribution are also investigated. A possible application of the model to predict the charged particle pseudorapidity distributions for the system size scan program proposed recently for the STAR experiment at RHIC is proposed.
nucl-thJ.Phys.G(2021)·17 citations
04
Finite-amplitude method for collective inertia in spontaneous fission
Kouhei Washiyama · Nobuo Hinohara · Takashi Nakatsukasa
Background: Microscopic description of spontaneous fission is one of the most challenging subjects in nuclear physics. It is necessary to evaluate the collective potential and the collective inertia along a fission path for a description of quantum tunneling in spontaneous or low-energy fission. In past studies of the fission dynamics based on nuclear energy density functional (EDF) theory, the collective inertia has been evaluated with the cranking approximation, which neglects dynamical residual effects. Purpose: The purpose is to provide a reliable and efficient method to include dynamical residual effects in the collective inertia for fission dynamics. Methods: We use the local quasiparticle random-phase approximation (LQRPA) to evaluate the collective inertia along a fission path obtained by the constrained Hartree-Fock-Bogoliubov method with the Skyrme EDF. The finite-amplitude method (FAM) with a contour integration technique enables us to efficiently compute the collective inertia in a large model space. Results: We evaluate the FAM-QRPA collective inertia along a symmetric fission path in $^{240}$ Pu and $^{256}$ Fm. The FAM-QRPA inertia is significantly larger than the one of the cranking approximation, and shows pronounced peaks around the ground state and the fission isomer. This is due to dynamical residual effects. Conclusions: To describe the spontaneous or low-energy fission, we provide a reliable and efficient method to construct the collective inertia with dynamical residual effects that have been neglected in most of EDF-based works in the past. We show the importance of dynamical residual effects to the collective inertia. This work will be a starting point for a systematic study of fission dynamics in heavy and superheavy nuclei to microscopically describe the nuclear large-amplitude collective motions.
nucl-thnucl-exPRC(2021)·26 citations
05
Nucleon-pair approximation with matrix representation
Y. Lei🇨🇳 · Y. Lu🇨🇳 · Y. M. Zhao🇨🇳
In this paper, we propose an approach of the nucleon-pair approximation (NPA), in which the collective nucleon pairs are represented in terms of antisymmetric matrices, and commutations between nucleon pairs are given by using matrix multiplication that avoids angular-momentum couplings and recouplings. Therefore the present approach significantly simplifies the NPA computation. Furthermore, it is formulated on the same footing with and without isospin.
nucl-thCPC(2021)·22 citations
06
Calculation of the 12C+12C sub-barrier fusion cross section in an imaginary time-dependent mean field theory
A. Bonasera · J. B. Natowitz
The 12C+12C sub-barrier fusion cross section is calculated within the framework of a Time Dependent Hartree-Fock (TDHF) based classical model using the Feynman Path Integral Method. The modified astrophysical S*-factor is compared to direct and indirect experimental results. A good agreement with the direct data is found. In the lower energy region, where recent analyses of experimental data obtained with the Trojan Horse Method (THM) lead to contrasting results, the model predicts an S* factor half way between those results. Low energy resonances revealed in the THM data are added to the calculation and the relative reaction rate in the Gamow region is calculated. The role of different resonances is discussed in detail and their influence on the reaction rate at temperatures relevant to stellar evolution is investigated.
nucl-thPRC(2020)·25 citations
07
Mass and radius relations of quarkyonic stars using an excluded volume model
Srimoyee Sen🇺🇸 · Lars Sivertsen🇺🇸
Inspired by the excluded volume model for isospin symmetric quarkyonic matter, we construct an `excluded volume' model for a charge neutral quarkyonic phase whose hadronic sector contains only neutrons. We refer to this model as quarkyonic neutron matter. We compute the equation of state for this model and solve the Tolman-Oppenhermer-Volkoff equations to obtain mass and radius relations relevant for neutron stars. The most straightforward extension of the model for symmetric quarkyonic matter to quarkyonic neutron matter does not satisfy the mass radius constraints from neutron star measurements. However, we show that by incorporating appropriate nuclear interactions in the excluded volume model one can produce mass-radius relations that lie within the constraints obtained from gravitational waves of binary neutron star mergers and maximum mass measurements of neutron stars.
↳ astro-ph.HEnucl-thApJ(2021)·29 citations
08
QCD phase structure in strong magnetic fields
H.-T. Ding🇨🇳 · S.-T. Li🇨🇳 · Q. Shi🇨🇳 · A. Tomiya🇺🇸 · X.-D. Wang🇨🇳 · Y. Zhang🇨🇳
In this proceedings we discuss the natural connection between the reduction of neutral pion mass in the vacuum, and the magnetic catalysis as well as the reduction of transition temperature in the external magnetic field. We also present the first results on fluctuations of and correlations among conserved charges in strong magnetic fields from lattice QCD computations.
↳ hep-lathep-phhep-thnucl-ex+1Acta Phys.Polon.Supp.(2021)·14 citations

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