Nuclear Theory·nucl-th

Tuesday·December 29, 2020

15 papers—9 primary·6 cross-listed

01
[Submitted on 24 Dec 2020]
Fission fragments intrinsic spins and their correlations
A. Bulgac · I. Abdurrahman · S. Jin · K. Godbey · N. Schunck · I. Stetcu
The intrinsic spins and their correlations are the least understood characteristics of fission fragments from both theoretical and experimental points of view. In many nuclear reactions the emerging fragments are typically excited and acquire an intrinsic excitation energy and an intrinsic spin depending on the type of the reactions and interaction mechanism. Both the intrinsic excitation energies and the fragments intrinsic spins and parities are controlled by the interaction mechanism and conservations laws, which lead to their correlations and determines the character of their de-excitation mechanism. We outline here a framework for the theoretical extraction of the intrinsic spin distributions of the fragments and their correlations within the fully microscopic real-time density functional theory formalism and illustrate it on the example of induced fission of $^{236}$ U and $^{240}$ Pu, using two nuclear energy density functionals. These fission fragment intrinsic spin distributions display new qualitative features previously not discussed in literature. Within this fully microscopic framework we extract for the first time the intrinsic spin distributions of fission fragments of $^{236}$ U and $^{240}$ Pu as well as the correlations of their intrinsic spins, which have been debated in literature for more than six decades with no definite conclusions so far.
Comments:
6 pages, 2 figures, published version
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2012.13422 [pdf]
PRL(2021)·67 citations
02
[Submitted on 26 Dec 2020]
Hyperheavy spherical and toroidal nuclei: the role of shell structure
S.E.Agbemava · A.V.Afanasjev
The properties of toroidal hyperheavy even-even nuclei and the role of toroidal shell structure are extensively studied within covariant density functional theory. The general trends in the evolution of toroidal shapes in the $Z \approx 130 - 180$ region of nuclear chart are established for the first time. These nuclei are stable with respect of breathing deformations. The most compact fat toroidal nuclei are located in the $Z \approx 136, N \approx 206$ region of nuclear chart, but thin toroidal nuclei become dominant with increasing proton number and on moving towards proton and neutron drip lines. The role of toroidal shell structure, its regularity, supershell structure, shell gaps as well as the role of different groups of the pairs of the orbitals in its formation are investigated in detail. The lowest in energy solutions at axial symmetry are characterized either by large shell gaps or low density of the single-particle states in the vicinity of the Fermi level in at least one of the subsystems (proton or neutron). Related quantum shell effects are expected to act against the instabilities in breathing and sausage deformations for these subsystems. The investigation with large set of covariant energy density functionals reveals that substantial proton $Z = 154$ and 186 and neutron $N = 228$ , 308 and 406 spherical shell gaps exist in all functionals. The nuclei in the vicinity of the combination of these particle numbers form the islands of stability of spherical hyperheavy nuclei. The study suggests that the $N = 210$ toroidal shell gap plays a substantial role in the stabilization of fat toroidal nuclei.
Comments:
25 pages, 19 figures, submitted to Physical Review C, revised version with suggestions of referee taken into account
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2012.13799 [pdf]
PRC(2021)·16 citations
03
[Submitted on 26 Dec 2020]
Calculating the initial energy density in heavy ion collisions by including the finite nuclear thickness
Todd Mendenhall🇺🇸 · Zi-Wei Lin🇺🇸
The initial energy density produced in heavy ion collisions can be estimated with the Bjorken energy density formula after choosing a proper formation time $τ_{F}$ . However, the Bjorken formula breaks down at low energies because it neglects the finite nuclear thickness. Here we include both the finite time duration and finite longitudinal extension of the initial energy production. When $τ_{F}$ is not too much smaller than the crossing time of the two nuclei, our results are similar to those from a previous study that only considers the finite time duration. In particular, we find that at low energies the initial energy density has a much lower maximum value but evolves much longer than the Bjorken formula, while at large-enough $τ_{F}$ and/or high-enough energies our result approaches the Bjorken formula. We also find a qualitative difference in that our maximum energy density $ϵ^{max}$ at $τ_{F} = 0$ is finite, while the Bjorken formula diverges as $1/ τ_{F}$ and the previous result diverges as $ln (1/ τ_{F})$ at low energies but as $1/ τ_{F}$ at high energies. Furthermore, our solution of the energy density approximately satisfies a scaling relation. As a result, the $τ_{F}$ -dependence of $ϵ^{max}$ determines the $A$ -dependence, and the weaker $τ_{F}$ -dependence of $ϵ^{max}$ in our results at low energies means a slower increase of $ϵ^{max}$ with $A$ .
Comments:
10 pages, 8 figures, 1 table; typos in Eq.(19) and Fig.8 corrected; final published version
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2012.13825 [pdf]
PRC(2021)·17 citations
04
[Submitted on 27 Dec 2020]
Radial profile of bottom quarks in jets in high-energy nuclear collisions
Sa Wang🇨🇳 · Wei Dai🇨🇳 · Ben-Wei Zhang🇨🇳 · Enke Wang🇨🇳
Angular correlations between heavy quark (HQ) and its tagged jet are potentially new tools to gain insight into the in-medium partonic interactions in relativistic heavy-ion collisions. In this work, we present the first theoretical study on the radial profiles of B mesons in jets in Pb+Pb collisions at the LHC. The initial production of bottom quark tagged jet in p+p is computed by SHERPA which matches the next-to-leading order matrix elements with contributions of parton shower, whereas the massive quark traversing the QGP described by a Monte Carlo model SHELL which can simultaneously simulate light and heavy flavor in-medium energy loss within the framework of Langevin evolution. In p+p collisions, we find that at lower $p_{T}^{Q}$ the radial profiles of heavy flavors in jets are sensitive to the heavy quark mass. In $0 - 10%$ Pb+Pb collisions at $s_{NN} = 5.02$ TeV, we observe an inverse modification pattern of the B mesons radial profiles in jets at $4 < p_{T}^{Q} < 20$ GeV compared to that of D mesons: the jet quenching effects narrow the jet radial profile of B mesons in jets while broaden that of D mesons in jets. We find that in A+A collisions, the contribution dissipated from the higher $p_{T}^{Q} > 20$ GeV region naturally has a narrower initial distribution and consequently leads to a narrower modification pattern of radial profile; however the diffusion nature of the heavy flavor in-medium interactions will give rise to a broader modification pattern of radial profile. These two effects consequently compete and offset with each other, and the b quarks in jets benefit more from the former and suffers less diffusion effect compared to that of c quarks in jets. These findings can be tested in the future experimental measurements at the LHC to gain better understanding of the mass effect of jet quenching.
Comments:
9 pages, 6 figures, a typo corrected
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2012.13935 [pdf]
CPC(2021)·22 citations
05
[Submitted on 28 Dec 2020]
Shape of 13C studied by the real-time evolution method
S. Shin · B. Zhou · M. Kimura
Background : Recently, Bijker et al. [Phys. Rev. Lett. 122, 162501 (2019)] explained the rotation-vibration spectrum of 13C by assuming triangular nuclear shape with D'3h symmetry. Purpose : The purpose of this work is to test the shape and symmetry of 13C based on a microscopic nuclear model without assumption of nuclear shape. Method : We have applied the real-time evolution method to 13C. By using the equation-of-motion of clusters, the model describes the 3alpha+n system without any assumption of symmetry. Results : REM described the low-lying states more accurately than the previous cluster model studies. The analysis of the wave functions showed that the ground band has approximate triangular symmetry, while the excited bands deviate from it. Conclusion : This work confirmed that the ground band has the intrinsic structure with the triangular arrangement of three alpha particles.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2012.14055 [pdf]
PRC(2021)·10 citations
06
[Submitted on 28 Dec 2020]
From finite nuclei to neutron stars : the essential role of high-order density dependence in effective forces
C.J. Jiang · Y. Qiang · D.W. Guan · Q.Z. Chai · C.Y. Qiao · J.C. Pei
A unified description of finite nuclei and equation of state of neutron stars present a major challenge as well as opportunities for understandings of nuclear interactions.Inspired by the Lee-Huang-Yang formula of hard-sphere gases, we developed effective nuclear interactions with an additional high-order density dependent term.The original Skyrme force SLy4 is widely used in studies of neutron stars but is not satisfied for global descriptions of finite nuclei. The refitted SLy4 $^{'}$ force can improve descriptions of finite nuclei but slightly reduces the radius of neutron star of 1.4 solar mass.We found that the extended SLy4 force with a higher-order density dependence can properly describe properties of both finite nuclei and GW170817 binary neutron stars, including the mass-radius relation and the tidal deformability. This demonstrated the essential role of high-order density dependence at ultrahigh densities. Our work provides a unified and predictive model for neutron stars, as well as new insights for the future development of effective interactions.
Comments:
5 pages, 3 figures, published in Chin. Phys. Lett. 2021, 38 (5): 052101
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2012.14083 [pdf]
Chin.Phys.Lett.(2021)·9 citations
07
[Submitted on 28 Dec 2020]
Towards modeling cluster structure of $^{8}$ Be with chiral interaction
Tokuro Fukui
How the nuclear force behaves in cluster states, in particular those consisting of the $α$ clusters, has been investigated so far, but not yet elucidated. Today the chiral effective field theory is established and it would shed new light on the microscopic understanding of the cluster states. We aim to address a possible source of the attraction in the cluster states of $^{8} Be$ in view of the pion exchange. Namely, we investigate whether the two-pion-exchange interaction acts as a dominant attraction in the $α + α$ system as predicted by a previous work. We describe theoretically the cluster structure of $^{8} Be$ by the Brink model, for which the effective interaction is designed from the realistic nuclear force derived through the chiral effective field theory. The two-body matrix elements of the chiral interaction with the local-Gaussian bases are formulated within the approximation of the spin-isospin saturation forming an $α$ particle. Introducing a global prefactor to the chiral interaction phenomenologically, the ground and low-lying excited states of $^{8} Be$ , the scattering phase shift of the $α$ - $α$ system as well, are satisfactorily depicted. The attraction in the cluster states is found to be stemming from the two-pion-exchange contributions dominantly, along with nonnegligible short-range terms. The present work can be the foundation towards constructing realistic cluster models, by which the cluster states will be revealed microscopically in the next step.
Comments:
38 pages, 11 figures, 8 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2012.14217 [pdf]
J.Phys.G(2022)·7 citations
08
[Submitted on 28 Dec 2020]
Role of {\alpha}-cluster transfer in formation 20Ne+16O cross sections at backward angles
Sh. Hamada · Nourhan M. Elmedalaa · I. Bondouk · N. Darwish
The experimental angular distributions for 20Ne+16O elastic transfer are reanalyzed using different forms of potential both phenomenological and semi-microscopic. The significant increase in cross sections at backward hemisphere due to the contribution of alphacluster transfer is investigated using the distorted wave Born approximation (DWBA) method. The spectroscopic amplitude (SA) for the configuration 20Ne as consisting of 16O (core) and an alpha-particle orbiting this core at the different concerned energies is extracted. The agreement between the experimental data and theoretical calculations using the two considered approaches is reasonably good.
Comments:
10 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2012.14260 [pdf]
Braz.J.Phys.(2021)·3 citations
09
[Submitted on 23 Dec 2020]
Relativistic levels of mesic atoms
Riccardo Giachetti🇮🇹 · Emanuele Sorace🇮🇹
We revisit the derivation of the covariant two-body scalar-fermion equation with a Coulomb interaction, presented in a previous paper. We show that it can be given the formal aspect of a Dirac equation, but for the fact that the eigenvalue is also contained in one of the coefficients and thus it is not linearly included. The discussion of the boundary value problem is therefore different, although some properties of the Dirac equation can be recovered in an approximation bringing back to the concept of reduced mass. We discuss a mixed analytic-numerical method of solution which allows to obtain very accurate results and we calculate the lowest levels, states and QED corrections for pionic and kaonic atoms.
Comments:
13 pages, 5 tables
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th)
arXiv:
2012.14299 [pdf]
Annals Phys.(2021)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE