Nuclear Theory·nucl-th

Monday·December 18, 2017

11 papers—8 primary·3 cross-listed

01
A 4-dimensional Langevin approach to low-energy nuclear fission of $^{236}$ U
Chikako Ishizuka · Mark D. Usang · Fedir A. Ivanyuk · Joachim A. Maruhn · Katsuhisa Nishio · Satoshi Chiba
We developed a four-dimensional Langevin model which can treat the deformation of each fragment independently and applied it to low energy fission of 236U, the compound system of the reaction n+ $^{235}$ U. The potential energy is calculated with the deformed two-centerWoods-Saxon (TCWS) and the Nilsson type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments $ν$ (A). Furthermore, the measured total kinetic energy TKE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several long-standing open problems in fission such as the sharing of the excitation energy between the fragments.
nucl-thnucl-exPRC(2017)·70 citations
02
Hauser-Feshbach fission fragment de-excitation with calculated macroscopic-microscopic mass yields
Patrick Jaffke · Peter Moller · Patrick Talou · Arnold J. Sierk
The Hauser-Feshbach statistical model is applied to the de-excitation of primary fission fragments using input mass yields calculated with macroscopic-microscopic models of the potential energy surface. We test the sensitivity of the prompt fission observables to the input mass yields for two important reactions, $^{235}$ U $(n_{th}, f)$ and $^{239}$ Pu $(n_{th}, f)$ , for which good experimental data exist. General traits of the mass yields, such as the location of the peaks and their widths, can impact both the prompt neutron and $γ$ -ray multiplicities, as well as their spectra. Specifically, we use several mass yields to determine a linear correlation between the calculated prompt neutron multiplicity $ν ˉ$ and the average heavy-fragment mass $⟨ A_{h} ⟩$ of the input mass yields $\partial ν ˉ / \partial ⟨ A_{h} ⟩ = \pm 0.1 n / f / u$ . The mass peak width influences the correlation between the total kinetic energy of the fission fragments and the total number of prompt neutrons emitted $ν ˉ_{T} (TKE)$ . Typical biases on prompt particle observables from using calculated mass yields instead of experimental ones are: $δ ν ˉ = 4%$ for the average prompt neutron multiplicity, $δ M ˉ_{γ} = 1%$ for the average prompt $γ$ -ray multiplicity, $δ ϵ ˉ_{n}^{LAB} = 1%$ for the average outgoing neutron energy, $δ ϵ ˉ_{γ} = 1%$ for the average $γ$ -ray energy, and $δ ⟨ TKE ⟩ = 0.4%$ for the average total kinetic energy of the fission fragments.
nucl-thPRC(2018)·22 citations
03
Massive neutron stars and $Λ$ -hypernuclei in relativistic mean field models
Ting-Ting Sun🇨🇳 · Cheng-Jun Xia🇨🇳 · Shi-Sheng Zhang🇨🇳 · M. S. Smith🇺🇸
Based on relativistic mean field (RMF) models, we study finite $Λ$ -hypernuclei and massive neutron stars. The effective $N$ - $N$ interactions PK1 and TM1 are adopted, while the $N$ - $Λ$ interactions are constrained by reproducing the binding energy of $Λ$ -hyperon at $1 s$ orbit of $_{Λ}^{40}$ Ca. It is found that the $Λ$ -meson couplings follow a simple relation, indicating a fixed $Λ$ potential well for symmetric nuclear matter at saturation densities, i.e., around $V_{Λ} = - 29.786$ MeV. With those interactions, a large mass range of $Λ$ -hypernuclei can be well described. Furthermore, the masses of PSR J1614-2230 and PSR J0348+0432 can be attained adopting the $Λ$ -meson couplings $g_{σ Λ} / g_{σ N} ≳ 0.73$ , $g_{ω Λ} / g_{ω N} ≳ 0.80$ for PK1 and $g_{σ Λ} / g_{σ N} ≳ 0.81$ , $g_{ω Λ} / g_{ω N} ≳ 0.90$ for TM1, respectively. This resolves the Hyperon Puzzle without introducing any additional degrees of freedom.
nucl-thCPC(2018)·37 citations
04
The three-pion decays of the $a_{1} (1260)$
Xu Zhang🇨🇳 · Ju-Jun Xie🇨🇳
We investigate the decay of $a_{1}^{+} (1260) \to π^{+} π^{+} π^{-}$ with the assumption that the $a_{1} (1260)$ is dynamically generated from the coupled channel $ρ π$ and $K ˉ K^{*}$ interactions. In addition to the tree level diagrams that proceed via $a_{1}^{+} (1260) \to ρ^{0} π^{+} \to π^{+} π^{+} π^{-}$ , we take into account also the final state interactions of $π π \to π π$ and $K K ˉ \to π π$ . We calculate the invariant $π^{+} π^{-}$ mass distribution and also the total decay width of $a_{1}^{+} (1260) \to π^{+} π^{+} π^{-}$ as a function of the mass of $a_{1} (1260)$ . The calculated total decay width of $a_{1} (1260)$ is significantly different from other model calculations and tied to the dynamical nature of the $a_{1} (1260)$ resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the $ρ π$ component in the $a_{1} (1260)$ wave function.
nucl-thhep-phnucl-exCommun.Theor.Phys.(2018)·12 citations
05
Analysis of the total kinetic energy of fission fragments with the Langevin equation
Mark Dennis Usang · Fedir Ivanyuk · Chikako Ishizuka · Satoshi Chiba
We analyzed the total kinetic energy (TKE) of fission fragments with three-dimensional Langevin calculations for a series of actinides and Fm isotopes at various excitation energies. This allowed us to establish systematic trends of TKE with $Z^{2} / A^{1/3}$ of the fissioning system and as a function of excitation energy. In the mass-energy distributions of fission fragments we see the contributions from the standard, super-long, and super-short (in the case of $^{258}$ Fm) fission modes. For the fission fragments mass distribution of $^{258}$ Fm we obtained a single peak mass distribution. The decomposition of TKE into the prescission kinetic energy and Coulomb repulsion showed that decrease of TKE with growing excitation energy is accompanied by a decrease of prescission kinetic energy. It was also found that transport coefficients (friction and inertia tensors) calculated by a microscopic model and by macroscopic models give drastically different behavior of TKE as a function of excitation energy. The results obtained with microscopic transport coefficients are much closer to experimental data than those calculated with macroscopic ones.
nucl-thPRC(2017)·55 citations
06
Onset of $η$ nuclear binding
Nir Barnea🇮🇱 · Betzalel Bazak🇮🇱 · Eliahu Friedman🇮🇱 · Avraham Gal🇮🇱 · Aleš Cieplý🇨🇿 · Jiří Mareš🇨🇿 · Martin Schäfer🇨🇿
Recent studies of $η$ nuclear quasibound states by the Jerusalem-Prague Collaboration are reviewed, focusing on stochastic variational method self consistent calculations of $η$ few-nucleon systems. These calculations suggest that a minimum value Re $a_{η N} \approx 1$ fm (0.7 fm) is needed to bind $η^{3}$ He ( $η^{4}$ He).
nucl-thhep-phnucl-exEPJ Web Conf.(2018)·2 citations
07
An Alpha Particle Model for Carbon-12
J. I. Rawlinson
We introduce a new model for the Carbon-12 nucleus and compute its lowest energy levels. Our model is inspired by previous work on the rigid body approximation in the $B = 12$ sector of the Skyrme model. We go beyond this approximation and treat the nucleus as a deformable body, finding several new states. A restricted set of deformations is considered, leading to a configuration space $C$ which has a graph-like structure. We use ideas from quantum graph theory in order to make sense of quantum mechanics on $C$ even though it is not a manifold. This is a new approach to Skyrmion quantisation and the method presented in this paper could be applied to a variety of other problems.
nucl-thhep-thNPA(2018)·26 citations
08
Hypernuclear No-Core Shell Model
Roland Wirth🇩🇪 · Daniel Gazda🇸🇪 · Petr Navrátil🇨🇦 · Robert Roth🇩🇪
We extend the No-Core Shell Model (NCSM) methodology to incorporate strangeness degrees of freedom and apply it to single- $Λ$ hypernuclei. After discussing the transformation of the hyperon-nucleon (YN) interaction into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group transformation applied to it to improve model-space convergence, we present two complementary formulations of the NCSM, one that uses relative Jacobi coordinates and symmetry-adapted basis states to fully exploit the symmetries of the hypernuclear Hamiltonian, and one working in a Slater determinant basis of HO states where antisymmetrization and computation of matrix elements is simple and to which an importance-truncation scheme can be applied. For the Jacobi-coordinate formulation, we give an iterative procedure for the construction of the antisymmetric basis for arbitrary particle number and present the formulae used to embed two- and three-baryon interactions into the many-body space. For the Slater-determinant formulation, we discuss the conversion of the YN interaction matrix elements from relative to single-particle coordinates, the importance-truncation scheme that tailors the model space to the description of the low-lying spectrum, and the role of the redundant center-of-mass degrees of freedom. We conclude with a validation of both formulations in the four-body system, giving converged ground-state energies for a chiral Hamiltonian, and present a short survey of the $A \leq 7$ hyper-helium isotopes.
nucl-thPRC(2018)·47 citations
09
The Photon in Dense Nuclear Matter I: Random Phase Approximation
Stephan Stetina🇦🇹 · Ermal Rrapaj🇺🇸 · Sanjay Reddy🇺🇸
We present a comprehensive and pedagogic discussion of the properties of photons in cold and dense nuclear matter based on the resummed one-loop photon self energy. Correlations between electrons, muons, protons and neutrons in beta equilibrium that arise due to electromagnetic and strong interactions are consistently taken into account within the random phase approximation. Screening effects and damping as well as collective excitations are systematically studied in a fully relativistic setup. Our study is relevant to linear response theory of dense nuclear matter, calculations of transport properties of cold dense matter and to investigations of the production and propagation of hypothetical vector bosons such as the dark photons.
↳ astro-ph.HEcond-mat.othernucl-thPRC(2018)·14 citations
10
Predictions on three-particle azimuthal correlations in proton-proton collisions
Şener Özönder🇹🇷
The ridge signal, which is long-ranged in rapidity, in the di-hadron correlations in high-multiplicity p-p and p-A collisions opened up a whole new research area in high-energy QCD. Although the ridge had been observed in A-A collisions and interpreted as a result of the radial flow of quark-gluon plasma, it had not appeared until recently in the data of small collision systems such as p-p and p-A, nor had it been predicted theoretically or seen in the event generators. There are two competing approaches that attempt to explain the systematics of the di-hadron ridge signal; hydrodynamics and gluon saturation physics (color glass condensate/glasma). In this work, we present predictions for the transverse momentum and rapidity dependence of the three-particle correlation function within the gluon saturation physics. Tri-hadron correlations can be measured, and the data can possibly rule out one of the two alternative approaches.
↳ hep-phnucl-thTurk.J.Phys.(2018)·7 citations
11
$Z_{c} (3900) / Z_{c} (3885)$ as a virtual state from $π J / ψ - D ˉ^{*} D$ interaction
Jun He🇨🇳 · Dian-Yong Chen🇨🇳
In this work, we study the $J / ψ π$ and $D ˉ^{*} D$ invariant mass spectra of the $Y (4260)$ decay to find out the origin of the $Z_{c} (3900)$ and $Z_{c} (3885)$ structures. The $J / ψ π - D ˉ^{*} D$ interaction is studied in a coupled-channel quasipotential Bethe-Saltpeter equation approach, and embedded to the $Y (4260)$ decay process to reproduce both $J / ψ π^{-}$ and $D^{*-} D^{0}$ invariant mass spectra observed at BESIII simultaneously. It is found out that a virtual state at energy about 3870 MeV is produced from the interaction when both invariant mass spectra are comparable with the experiment. The results support that both $Z_{c} (3900)$ and $Z_{c} (3885)$ have the same origin, that is, a virtual state from $J / ψ π - D ˉ^{*} D$ interaction, in which the $D ˉ^{*} D$ interaction is more important and the coupling between $D ˉ^{*} D$ and $J / ψ π$ channels plays a minor role.
↳ hep-phnucl-thEPJC(2018)·43 citations

Affiliations

first authorsco-authorsvia INSPIRE