Nuclear Theory·nucl-th

Tuesday·December 16, 2014

13 papers—7 primary·6 cross-listed

01
[Submitted on 13 Dec 2014]
Decay and structure of the Hoyle state
Souichi Ishikawa
The first $0^{+}$ resonant state of the $^{12}$ C nucleus $^{12}$ C $(0_{2}^{+})$ , so called the Hoyle state, is investigated in a three- $α$ -particle (3- $α$ ) model. A wave function for the photodisintegration reaction of a $^{12}$ C bound state to 3- $α$ final states is defined and calculated by the Faddeev three-body formalism, in which three-body bound- and continuum states are treated consistently. From the wave function at the Hoyle state energy, I calculated distributions of outgoing $α$ -particles and density distributions at interior region of the Hoyle state. Results show that a process through a two- $α$ resonant state is dominant in the decay and contributions of the rest process are very small, less than 1 \%. There appear some peaks in the interior density distribution corresponding to configurations of an equilateral- and an isosceles triangles. It turns out that these results are obtained independently of the choice of $α$ -particle interaction models, when they are made to reproduce the Hoyle state energy.
Comments:
5 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1412.4176 [pdf]
PRC(2014)·56 citations
02
[Submitted on 13 Dec 2014]
Triaxially deformed relativistic point-coupling model for $Λ$ hypernuclei: a quantitative analysis of hyperon impurity effect on nuclear collective properties
W. X. Xue🇨🇳 · J. M. Yao🇨🇳 · K. Hagino🇯🇵 · Z. P. Li🇨🇳 · H. Mei🇨🇳 · Y. Tanimura🇫🇷
The impurity effect of hyperon on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of $E 2$ transition strength in low-lying states of hypernucleus $_{Λ}^{7}$ Li. Many more data on low-lying states of $Λ$ hypernuclei will be measured soon for $s d$ -shell nuclei, providing good opportunities to study the $Λ$ impurity effect on nuclear low-energy excitations. We carry out a quantitative analysis of $Λ$ hyperon impurity effect on the low-lying states of $s d$ -shell nuclei at the beyond-mean-field level based on a relativistic point-coupling energy density functional (EDF), considering that the $Λ$ hyperon is injected into the lowest positive-parity ( $Λ_{s}$ ) and negative-parity ( $Λ_{p}$ ) states. We adopt a triaxially deformed relativistic mean-field (RMF) approach for hypernuclei and calculate the $Λ$ binding energies of hypernuclei as well as the potential energy surfaces (PESs) in $(β, γ)$ deformation plane. We also calculate the PESs for the $Λ$ hypernuclei with good quantum numbers using a microscopic particle rotor model (PRM) with the same relativistic EDF. The triaxially deformed RMF approach is further applied in order to determine the parameters of a five-dimensional collective Hamiltonian (5DCH) for the collective excitations of triaxially deformed core nuclei. Taking $_{Λ}^{25, 27}$ Mg and $_{Λ}^{31}$ Si as examples, we analyse the impurity effects of $Λ_{s}$ and $Λ_{p}$ on the low-lying states of the core nuclei...
Comments:
15 pages with 18 figures and 1 table (version to be published in Physical Review C)
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1412.4201 [pdf]
PRC(2015)·32 citations
03
[Submitted on 15 Dec 2014]
Hyperons in neutron star matter within relativistic mean-field models
M. Oertel🇫🇷 · C. Providência🇵🇹 · F. Gulminelli🇫🇷 · A. R. Raduta🇷🇴
Since the discovery of neutron stars with masses around 2 solar masses the composition of matter in the central part of these massive stars has been intensively discussed. Within this paper we will (re)investigate the question of the appearance of hyperons. To that end we will perform an extensive parameter study within relativistic mean field models. We will show that it is possible to obtain high mass neutron stars (i) with a substantial amount of hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses, and (iii) a spinodal instability at the onset of hyperons. The results depend strongly on the interaction in the hyperon-hyperon channels, on which only very little information is available from terrestrial experiments up to now.
Comments:
15 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1412.4545 [pdf]
J.Phys.G(2015)·166 citations
04
[Submitted on 15 Dec 2014]
Hidden dibaryons in one- and two-pion production in NN collisions
M. N. Platonova🇷🇺 · V. I. Kukulin🇷🇺
Processes of one- and two-pion production in $N N$ collisions are considered in connection with excitation of intermediate dibaryon resonances. In particular, relative contributions of the conventional meson-exchange and dibaryon excitation mechanisms in the reaction $pp \to d π^{+}$ are investigated in detail. Inclusion of the intermediate isovector dibaryon resonances is shown to essentially improve the description of experimental data for this reaction, provided the soft meson-baryon form factors consistent with $π N$ elastic scattering are used. Manifestation of the intermediate isoscalar and isovector dibaryons in the two-pion production processes is also studied. The role of the isovector dibaryon resonances in the reaction $pp \to pp π π$ is discussed for the first time. An explanation of the observed strong differences between two-pion production cross sections in $p n$ and $pp$ collisions based in part on the analysis of dibaryon structure is suggested.
Comments:
Version accepted for publication in Nuclear Physics A
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1412.4574 [pdf]
NPA(2016)·45 citations
05
[Submitted on 15 Dec 2014]
Precision nucleon-nucleon potential at fifth order in the chiral expansion
E. Epelbaum🇩🇪 · H. Krebs🇩🇪 · U.-G. Meißner🇩🇪
We present a nucleon-nucleon potential at fifth order in chiral effective field theory. We find a substantial improvement in the description of nucleon-nucleon phase shifts as compared to the fourth-order results of Ref. [E. Epelbaum, H. Krebs, U.-G. Meißner, arXiv:1412.0142 [nucl-th]]. This provides clear evidence of the corresponding two-pion exchange contributions with all low-energy constants being determined from pion-nucleon scattering. The fifth-order corrections to nucleon-nucleon observables appear to be of a natural size which confirms the good convergence of the chiral expansion for nuclear forces. Furthermore, the obtained results provide strong support for the novel way of quantifying the theoretical uncertainty due to the truncation of the chiral expansion proposed in Ref. [E. Epelbaum, H. Krebs, U.-G. Meißner, arXiv:1412.0142 [nucl-th]]. Our work opens up new perspectives for precision ab initio calculations in few- and many-nucleon systems and is especially relevant for ongoing efforts towards a quantitative understanding the structure of the three-nucleon force in the framework of chiral effective field theory.
Comments:
5 pages, 4 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1412.4623 [pdf]
PRL(2015)·444 citations
06
[Submitted on 15 Dec 2014]
Low-energy excitations and quasielastic contribution to electron-nucleus and neutrino-nucleus scattering in the continuum random phase approximation
V. Pandey🇧🇪 · N. Jachowicz🇧🇪 · T. Van Cuyck🇧🇪 · J. Ryckebusch🇧🇪 · M. Martini🇧🇪
We present a detailed study of a continuum random phase approximation approach to quasielastic electron-nucleus and neutrino-nucleus scattering. The formalism is validated by confronting ( $e, e^{'}$ ) cross-section predictions with electron scattering data for the nuclear targets $^{12}$ C, $^{16}$ O, and $^{40}$ Ca, in the kinematic region where quasielastic scattering is expected to dominate. We examine the longitudinal and transverse contributions to $^{12}$ C( $e, e^{'}$ ) and compare them with the available data. Further, we study the $^{12}$ C( $ν_{μ}, μ^{-}$ ) cross sections relevant for accelerator-based neutrino-oscillation experiments. We pay special attention to low-energy excitations which can account for non-negligible contributions in measurements, and require a beyond-Fermi-gas formalism.
Comments:
10 pages, 14 figures. Version published in Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1412.4624 [pdf]
PRC(2015)·122 citations
07
[Submitted on 15 Dec 2014]
Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions
J. Scott Moreland🇺🇸 · Jonah E. Bernhard🇺🇸 · Steffen A. Bass🇺🇸
We introduce TRENTO, a new parametric initial condition model for high-energy nuclear collisions based on eikonal entropy deposition via a "reduced thickness" function. The model simultaneously describes experimental proton-proton, proton-nucleus, and nucleus-nucleus multiplicity distributions, and generates nucleus-nucleus eccentricity harmonics consistent with experimental flow constraints. In addition, the model is compatible with ultra-central uranium-uranium data unlike existing models that include binary collision terms.
Comments:
6 pages, 5 figures. This version has a new title, significant revisions to the introduction and conclusion, and new figures 1-3. The presented model is available at https://github.com/Duke-QCD/trento
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1412.4708 [pdf]
PRC(2015)·602 citations

Affiliations

first authorsco-authorsvia INSPIRE

Decay and structure of the Hoyle state

Triaxially deformed relativistic point-coupling model for Λ hypernuclei: a quantitative analysis of hyperon impurity effect on nuclear collective properties

Hyperons in neutron star matter within relativistic mean-field models

Hidden dibaryons in one- and two-pion production in NN collisions

Precision nucleon-nucleon potential at fifth order in the chiral expansion

Low-energy excitations and quasielastic contribution to electron-nucleus and neutrino-nucleus scattering in the continuum random phase approximation

Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions

Affiliations

Triaxially deformed relativistic point-coupling model for $Λ$ hypernuclei: a quantitative analysis of hyperon impurity effect on nuclear collective properties