Nuclear Theory·nucl-th

Wednesday·September 4, 2019

18 papers—6 primary·12 cross-listed

01
[Submitted on 31 Aug 2019]
Magic numbers of cylindrical symmetry
Andriana Martinou · Dennis Bonatsos
In nuclear physics a magic number is defined as the nucleon number, which is separated by a significantly large single-particle energy gap from the next nucleon. Magic numbers define the nuclear shells, which are considered to be active, only if they are partially occupied by nucleons. As a consequence the single particle interactions of the valence nucleons lead to the description of the collective properties of the whole nucleus in the shell model theory. But phenomena as the island of inversion, the shape coexistence and the break down of the N=20 magic number reveal that the above definition of a magic number is deficient. A complementary definition should rely on the selection rules of the single particle interactions. Specifically the selection rules of the quadrupole-quadrupole interaction lead to two sets of magic numbers, namely the harmonic oscillator magic numbers 2, 8 20, 40, 70, 112, ... and the spin-orbit SO-like magic numbers 2, 6, 14, 28, 50, 82, 126, ... The underlying symmetries are respectively the spherical symmetry of the 3D isotropic harmonic oscillator and the cylindrical symmetry of the 3D anisotropic harmonic oscillator with two frequencies equal. The above two sets of magic numbers along with the Elliott SU(3) symmetry framework predict long standing and puzzling phenomena in nuclear physics.
Comments:
25 pages, 2 figures, 6 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1909.00233 [pdf]
2 citations
02
[Submitted on 31 Aug 2019]
The Shape of the Correlation Function
Jakub Cimerman🇨🇿 · Boris Tomášik🇸🇰 · Christopher Plumberg🇸🇪
The correlation function measured in ultrarelativistic nuclear collisions is non-Gaussian. By making use of models we discuss and assess how much various effects can influence its shape. In particular, we focus on the parametrisations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as non-spherical shape, resonance decays, event-by-event fluctuations and functional dependence on $Q_{in v}$ or similar.
Comments:
proceedings from the XIV Workshop on Particle Correlations and Femtoscopy, WPCF 2019, Dubna, Russia, June 3-7, 2019
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1909.00278 [pdf]
Phys.Part.Nucl.(2020)·6 citations
03
[Submitted on 1 Sept 2019]
Color transparency in $p ˉ d \to π^{-} π^{0} p$ reaction
A.B. Larionov🇩🇪 · M. Strikman🇺🇸
We consider exclusive two-pion production in antiproton-deuteron interactions at the beam momenta around 10 GeV/c in the kinematics with large momentum transfer in the underlying hard process $p ˉ n \to π^{-} π^{0}$ . The calculations are performed taking into account the antiproton and pion soft rescattering on the spectator proton in the framework of the generalized eikonal approximation. We focus on the color transparency effect that is modeled by introducing the dependence of rescattering amplitudes on the relative position of the struck and spectator nucleons along the momentum of a fast particle. As a consequence of the interplay between the impulse approximation and rescattering amplitudes the nuclear transparency ratio reveals a pretty complicated behaviour as a function of the transverse momentum of the spectator proton and the relative azimuthal angle between the $π^{-}$ -meson and the proton. Color transparency significantly suppresses rescattering amplitudes which leads to substantial modifications of the nuclear transparency ratio moving it closer to the value obtained in the impulse approximation. By performing the Monte-Carlo analysis we determine that this effect can be studied at PANDA with a reasonable statistics.
Comments:
30 pages, 10 figures, revised sec. 1 and 2, results unchanged, version accepted in EPJA
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1909.00379 [pdf]
EPJA(2020)·7 citations
04
[Submitted on 2 Sept 2019]
Effective interactions in the sd shell
Nadezda A. Smirnova🇫🇷 · Bruce R. Barrett🇺🇸 · Youngman Kim🇰🇷 · Ik Jae Shin🇰🇷 · Andrey M. Shirokov🇺🇸 · Erdal Dikmen🇹🇷 · Pieter Maris🇺🇸 · James P. Vary🇺🇸
We perform a quantitative study of the microscopic effective shell-model interactions in the valence sd shell, obtained from modern nucleon-nucleon potentials, chiral N3LO, JISP16 and Daejeon16, using No-Core Shell-Model wave functions and the Okubo-Lee-Suzuki transformation. We investigate the monopole properties of those interactions in comparison with the phenomenological universal sd-shell interaction, USDB. Theoretical binding energies and low-energy spectra of O isotopes and of selected sd-shell nuclei, are presented. We conclude that there is a noticeable improvement in the quality of the effective interaction when it is derived from the Daejeon16 potential. We show that its proton-neutron centroids are consistent with those from USDB. We then propose monopole modifications of the Daejeon16 centroids in order to provide an adjusted interaction yielding significantly improved agreement with the experiment. A spin-tensor decomposition of two-body effective interactions is applied in order to extract more information on the structure of the centroids and to understand the reason for deficiencies arising from our current theoretical approximations. The issue of the possible role of the three-nucleon forces is addressed.
Comments:
22 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1909.00628 [pdf]
PRC(2019)·37 citations
05
[Submitted on 2 Sept 2019]
The quest of shape coexistence in Zr isotopes
J.E. Garcia-Ramos · K. Heyde
The mass region with A~100 and Z~40 is known to experience a sudden onset of deformation. The presence of the subshell closure $Z = 40$ makes feasible to create particle-hole excitations at a moderate excitation energy and, therefore, likely intruder states could be present in the low-lying spectrum. In other words, shape coexistence is expected to be a key ingredient to understand this mass region. The aim of this work is to describe excitation energies, transition rates, radii, and two-neutron separation energies for the even-even 94-110Zr nuclei and, moreover, to obtain information about wave functions and deformation. The interacting boson model with configuration mixing will be the framework to study the even-even Zr nuclei, considering only two types of configurations: 0particle-0hole and 2p-2h excitations. On one hand, the parameters appearing in the Hamiltonian and in the E2 transition operator are fixed trough a least-squares fit to the whole available experimental information. On the other hand, once the parameters have been fixed, the calculations allow to obtain a complete set of observables for the whole even-even Zr chain of isotopes. Spectra, transition rates, radii, $ρ^{2} (E 0)$ , and two-neutron separation energies have been calculated and a good agreement with the experimental information has been obtained. Moreover, a detailed study of the wave function has been conducted and mean-field energy surfaces and deformation have been computed too. The importance of shape coexistence has been shown to correctly describe the A~100 mass area for even-even Zr nuclei. This work confirmed the rather spherical nature of the ground state of 94-98Zr and its deformed nature for 100-110Zr isotopes. The sudden onset of deformation in 100Zr is owing to the rapid lowering of a deformed (intruder) configuration which is high-lying in lighter isotopes.
Comments:
Submitted to PRC
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1909.00824 [pdf]
PRC(2019)·58 citations
06
[Submitted on 2 Sept 2019]
Complex phase structure of the meson-baryon $T$ -matrix
Shahab Razavi🇺🇸 · K. Nakayama🇺🇸
The full complex phase structure of the meson-baryon reaction amplitude in coupled channels approach is investigated, including also the photon-baryon channel. The result may be viewed as a generalization of the well-known Watson's theorem. Furthermore, the complex phase structure is exhibited for the pole and nonpole parts of the reaction amplitude in such a way that it will serve as a convenient common starting point for constructing models with different levels of approximation, in particular, for building isobar models where the basic properties of the $S$ -matrix can be maintained. Such models should be useful, especially, in coupled multichannel calculations, where a large amount of experimental data are considered in resonance analyses, a situation encountered in modern baryon spectroscopy. In particular, it is shown that the unitarity of the pole part of the $T$ -matrix arises automatically from the dressing mechanism inherent in the basic scattering equation. This implies that no separate conditions are required for making this part of the resonance amplitude unitary as it has been done in some of the existing isobar models.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1909.00869 [pdf]
PRD(2019)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE

Magic numbers of cylindrical symmetry

The Shape of the Correlation Function

Color transparency in pˉ​d→π−π0p reaction

Effective interactions in the sd shell

The quest of shape coexistence in Zr isotopes

Complex phase structure of the meson-baryon T-matrix

Affiliations

Color transparency in $p ˉ d \to π^{-} π^{0} p$ reaction

Complex phase structure of the meson-baryon $T$ -matrix