Nuclear Theory·nucl-th

Thursday·March 24, 2016

10 papers—8 primary·2 cross-listed

01
[Submitted on 22 Mar 2016]
Meaning of the nuclear wave function
John D. Terry🇺🇸 · Gerald A. Miller🇺🇸
Background The intense current experimental interest in studying the structure of the deuteron and using it to enable accurate studies of neutron structure motivate us to examine the four-dimensional space-time nature of the nuclear wave function, and the various approximations used to reduce it to an object that depends only on three spatial variables. Purpose: The aim is to determine if the ability to understand and analyze measured experimental cross sections is compromised by making the reduction from four to three dimensions. Method: Simple, exactly-calculable, covariant models of a bound-state wave state wave function (a scalar boson made of two constituent-scalar bosons) with parameters chosen to represent a deuteron are used to investigate the accuracy of using different approximations to the nuclear wave function to compute the quasi-elastic scattering cross section. Four different versions of the wave function are defined (light-front spectator, light-front, light-front with scaling and non-relativistic) and used to compute the cross sections as a function of how far off the mass-shell (how virtual) is the struck constituent. Results: We show that making an exact calculation of the quasi-elastic scattering cross section involves using the light-front spectator wave function. All of the other approaches fail to reproduce the model exact calculation if the value of Bjorken $x$ differs from unity. The model is extended to consider an essential effect of spin to show that constituent nucleons cannot be treated as being on their mass shell even when taking the matrix element of a `good' current. Conclusions: It is necessary to develop realistic light-front spectator wave functions to meet the needs of current and planned experiments.
Comments:
17 pages 11 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1603.07032 [pdf]
PRC(2016)·1 citation
02
[Submitted on 23 Mar 2016]
Mesons in Nuclei and Partial Restoration of Chiral Symmetry
Daisuke Jido (Tokyo Metropolitan University)🇯🇵
Recent topics on mesons in nuclei are discussed by especially emphasizing the role of the partial restoration of chiral symmetry in the nuclear medium. The spontaneously broken chiral symmetry in vacuum is considered to be incompletely restored in finite nuclear density systems with moderate reduction of the magnitude of the quark condensate. On the partial restoration of chiral symmetry, the wave function renormalization is important to be taken into account for the Nambu-Goldstone bosons. We also discuss the possible change of the meson properties in the nuclear medium and meson-nucleus systems for the $K ˉ$ , $η$ , $K^{+}$ and $η^{'}$ mesons.
Comments:
9 pages, 4 figures. Contribution to the proceedings of The 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015), Sendai, Japan, September 7-12, 2015
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07083 [pdf]
JPS Conf.Proc.(2017)·4 citations
03
[Submitted on 23 Mar 2016]
Extended systematics of alpha decay half lives for exotic superheavy nuclei
A. I. Budaca · R. Budaca · I. Silisteanu
The experimentally available data on the alpha decay half lives and Q? values for 96 superheavy nuclei are used to fix the parameters for a modified version of the Brown empirical formula through two fitting procedures which enables its comparison with similar fits using Viola-Seaborg and Royer formulas. The new expressions provide very good agreement with experimental data having fewer or the same number of parameters. All formulas with the obtained parameters are then extrapolated to generate half lives predictions for 125 unknown superheavy alpha emitters. The nuclei where the employed empirical formulas maximally or minimally diverge are pointed out and a selection of 36 nuclei with exceptional superposition of predictions was made for experimental reference.
Comments:
18 pages, 5 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07091 [pdf]
NPA(2016)·82 citations
04
[Submitted on 23 Mar 2016]
Next-to-leading order effective field theory $Λ N \to N N$ potential in coordinate space
Axel Pérez-Obiol🇨🇿 · David R. Entem🇪🇸 · Bruno Juliá-Díaz🇪🇸 · Assumpta Parreño🇪🇸
The potential in coordinate space for the $Λ N \to N N$ weak transition, which drives the weak decay of most hypernuclei, is derived within the effective field theory formalism up to next-to-leading order. This coordinate space potential allows us to discuss how the different contributions to the potential add up at the different scales. Explicit expressions are given for each two-pion-exchange diagram contributing to the interaction. The potential is also reorganized into spin and isospin operators, and the coefficient for each operator is given in analytical form and represented in coordinate space. The relevance of explicitly including the mass differences among the baryons appearing in the two-pion-exchange diagrams is also discussed in detail.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07108 [pdf]
NPA(2016)·2 citations
05
[Submitted on 23 Mar 2016]
Isospin dynamics on neck fragmentation in isotopic nuclear reactions
Zhao-Qing Feng
The neck dynamics in Fermi-energy heavy-ion collisions, to probe the nuclear symmetry energy in the domain of sub-saturation densities, is investigated within an isospin dependent transport model. The single and double ratios of neutron/proton from free nucleons and light clusters (complex particles) in the isotopic reactions are analyzed systematically. Isospin effects of particles produced from the neck fragmentations are explored, which are constrained within the midrapidities ( $∣ y / y_{p r o j} ∣ <$ 0.3) and azimuthal angles (70 $^{o} \sim$ 110 $^{o}$ , 250 $^{o} \sim$ 290 $^{o}$ ) in semiperipheral nuclear collisions. It is found that the ratios of the energetic isospin particles strongly depend on the stiffness of nuclear symmetry energy and the effects increase with softening the symmetry energy, which would be a nice probe for extracting the symmetry energy below the normal density in experimentally. A flat structure appears at the tail spectra from the double ratio distributions. The neutron to proton ratio of light intermediate mass fragments (IMFs) with charged number Z $\leq$ 8 is related to the density dependence of symmetry energy with less sensitivity in comparison to the isospin ratios of nucleons and light particles.
Comments:
6 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07138 [pdf]
PRC(2016)·21 citations
06
[Submitted on 23 Mar 2016]
Correlations of $πN$ Partial Waves for Multi-Reaction Analyses
M. Döring🇺🇸 · J. Revier🇺🇸 · D. Rönchen🇩🇪 · R. Workman🇺🇸
In the search for missing baryonic resonances, many analyses include data from a variety of pion- and photon-induced reactions. For elastic $π N$ scattering, however, usually the partial waves of the SAID or other groups are fitted, instead of data. We provide the partial-wave covariance matrices needed to perform correlated $χ^{2}$ fits, in which the obtained $χ^{2}$ equals the actual $χ^{2}$ up non-linear and normalization corrections. For any analysis relying on partial waves extracted from elastic pion scattering, this is a prerequisite to assess the significance of resonance signals and to assign any uncertainty on results. The influence of systematic errors is also considered.
Comments:
7 pages, 3 figures; Acknowledgements updated
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1603.07265 [pdf]
PRC(2016)·18 citations
07
[Submitted on 23 Mar 2016]
Empirical residual neutron-proton interaction in odd-odd nuclei
Zheying Wu · S.A. Changizi · Chong Qi
Two types of average neutron-proton interaction formulas are compared: In the first type, neutron-proton interactions for even-even and odd- $A$ nuclei extracted from experimental binding energies show a smooth behavior as a function of mass number $A$ and are dominated by the contribution from the symmetry energy. Whereas in the second type large systematic staggering is seen between even- $A$ and odd- $A$ nuclei. This deviation is understood in term of the additional neutron-proton interaction in odd-odd nuclei relative to the neighboring even-even and odd- $A$ systems. We explore three possible ways to extract this additional interaction from the binding energy difference of neighboring nuclei. The extracted interactions are positive in nearly all cases and show weak dependence on the mass number. The empirical interactions are also compared with theoretical values extracted from recent nuclear mass models where large unexpected fluctuations are seen in certain nuclei. The reproduction of the residual neutron-proton interaction and the correction of those irregular fluctuations can be a good criterion for the refinement of those mass models.
Comments:
5 pages, 6 figures, to appear in PRC
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07290 [pdf]
PRC(2016)·22 citations
08
[Submitted on 23 Mar 2016]
$N = Z$ nuclei: A laboratory for neutron-proton collective mode
Chong Qi · R. Wyss
The neutron-neutron and proton-proton pairing correlations have long been recognised to be the dominant many-body correlation beyond the nuclear mean field since the introduction of pairing mechanism by Bohr, Mottelson and Pines nearly 60 year ago. Nevertheless, few conclusion has been reached concerning the existence of analogous neutron-proton (np) pair correlated state. One can see a renaissance in np correlation studies in relation to the significant progress in radioactive ion beam facilities and detection techniques. The np pairs can couple isospin T = 1 (isovector) or 0 (isoscalar). In the isovector channel, the angular momentum zero component is expected to be the most importance one. On the other hand, as one may infer from the general properties of the np two-body interaction, in the isoscalar channel, both the np pairs with minimum (J=1) and maximum (J=2j) spin values can be important. In this contribution, we will discuss the possible evidence for np pair coupling from different perspective and analyze its influence on interesting phenomena including the Wigner effect and mass correlations in odd-odd nuclei. In particular, we will explain the spin-aligned pair coupling scheme and quartet coupling involving pairs with maximum (J=2j) spin values.
Comments:
19 pages,15 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1603.07296 [pdf]
Phys.Scripta(2016)·37 citations

Affiliations

first authorsco-authorsvia INSPIRE