Nuclear Theory·nucl-th

Tuesday·September 18, 2018

15 papers—11 primary·4 cross-listed

01
[Submitted on 14 Sept 2018]
Parameter Optimization and Uncertainty Analysis of FREYA for Spontaneous Fission
Jackson Van Dyke · Lee Bernstein · Ramona Vogt
Background: The complete event fission simulation code FREYA is used to study correlations in fission. To make the best possible simulations, FREYA one must find the optimized values of the five physics-based parameters which characterize the events produced by FREYA. So far this has been done only empirically or by brute force computational techniques. Purpose: We seek to develop a method of parameter optimization for FREYA that would include uncertainty quantification and an analysis of the correlations between the parameters. Methods: We focus on spontaneous fission as a simpler test case of the method. We first check the results of previous optimizations for $^{252}$ Cf(sf) and then go on to develop a simulated annealing approach to optimize the parameters. Although $^{252}$ Cf(sf) has the most measured observables, we are able to apply the technique to all spontaneously fissioning isotopes in the current version of FREYA. Results: We find optimal values of the five FREYA parameters, with uncertainties, for all isotopes studied. Our results are compared with available data. The parameter values are physically reasonable and in accord with intuition, even in cases where the data for optimization are sparse to non-existent. Conclusions: The simulated annealing method provides a way to determine the best parameters for the phenomenologically-successful fission model FREYA. We have developed an algorithm that can be updated to include additional isotopes or more data sets for the current isotopes as they become available.
Comments:
To be published in Nuclear Instruments and Methods in Physics Research (http://authors.elsevier.com/sd/article/S0168900219300014)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.05587 [pdf]
Nucl.Instrum.Meth.A(2019)·2 citations
02
[Submitted on 15 Sept 2018]
Thermodynamic Geometry of Strongly Interacting Matter
P. Castorina🇮🇹 · M. Imbrosciano🇮🇹 · D. Lanteri🇮🇹
The thermodynamic geometry formalism is applied to strongly interacting matter to estimate the deconfinement temperature. The curved thermodynamic metric for Quantum Chromodynamics (QCD) is evaluated on the basis of lattice data, whereas the hadron resonance gas model is used for the hadronic sector. Since the deconfinement transition is a crossover, the geometric criterion used to define the \mbox{(pseudo-)critical} temperature, as a function of the baryonchemical potential $μ_{B}$ , is $R (T, μ_{B}) = 0$ , where $R$ is the scalar curvature. The (pseudo-)critical temperature, $T_{c}$ , resulting from QCD thermodynamic geometry is in good agreement with lattice and phenomenological freeze-out temperature estimates. The crossing temperature, $T_{h}$ , evaluated by the hadron resonance gas, which suffers of some model dependence, is larger than $T_{c}$ (about $20%$ ) signaling remnants of confinement above the transition.
Comments:
12 pages, 5 figs
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1809.05660 [pdf]
PRD(2018)·10 citations
03
[Submitted on 15 Sept 2018]
Soft rescattering in the timelike proton form factor within a spacetime scheme
Andrea Bianconi🇮🇹 · Egle Tomasi-Gustafsson🇫🇷
The annihilation of a lepton pair into a proton-antiproton pair, and the reverse process, allow for a measurement of the timelike proton form factors. This work aims at studying the corrections due to direct soft interactions between the proton and the antiproton before their annihilation or after their creation. The analysis is carried on in the spacetime formalism used by us in a series of recent works on timelike FFs. In particular the effect of $p ˉ p$ annihilation into many-meson states is considered. We expect it to determine similar real and imaginary parts for the form factor near the $p ˉ p$ channel threshold. We also discuss the possibility that the timelike FF differ by a phase in the hadron pair production and annihilation.
Comments:
19 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1809.05709 [pdf]
PRC(2018)·3 citations
04
[Submitted on 16 Sept 2018]
Low-Energy Heavy-Ion Reactions and the Skyrme Effective Interaction
P. D. Stevenson · M. C. Barton
The Skyrme effective interaction, with its multitude of parameterisations, along with its implemen- tation using the static and time-dependent density functional (TDHF) formalism have allowed for a range of microscopic calculations of low-energy heavy-ion collisions. These calculations allow variation of the effective interaction along with an interpretation of the results of this variation informed by a comparison to experimental data. Initial progress in implementing TDHF for heavy-ion collisions necessarily used many approximations in the geometry or the interaction. Over the last decade or so, the implementations have overcome all restrictions, and studies have begun to be made where details of the effective interaction are being probed. This review surveys these studies in low energy heavy-ion reactions, finding significant effects on observables from the form of the spin-orbit interaction, the use of the tensor force, and the inclusion of time-odd terms in the density functional.
Comments:
submitted to Prog. Part. Nucl. Phys
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.05801 [pdf]
PPNP(2019)·78 citations
05
[Submitted on 16 Sept 2018]
Response functions of hot and dense matter in the Nambu-Jona-Lasino model
Chengfu Mu🇨🇳 · Ziyue Wang🇨🇳 · Lianyi He🇨🇳
We investigate the current-current correlation functions or the so-called response functions of a two-flavor Nambu-Jona-Lasino model at finite temperature and density. We study the linear response by using the functional path integral approach and introducing the conjugated gauge fields as external sources. The response functions can be obtained by expanding the generational functional in powers of the external sources. We derive the response functions parallel to two well-established approximations for the equilibrium thermodynamics: the mean-field theory and a beyond-mean-field theory taking into account the mesonic contributions. The response functions based on the mean-field theory recover the so-called quasiparticle random phase approximation. We calculate the dynamical structure factors for the density responses in various channels within the random phase approximation. We show that the dynamical structure factors in the baryon axial vector and isospin axial vector channels can be used reveal the quark mass gap and the Mott dissociation of mesons, respectively. Noting that the mesonic contributions are not taken into account in the random phase approximation, we also derive the response functions parallel to the beyond-mean-field theory. We show that the mesonic fluctuations naturally give rise to three kinds of famous diagrammatic contributions: the Aslamazov-Lakin contribution, the Self-Energy or Density-of-State contribution, and the Maki-Thompson contribution. Unlike the equilibrium case, in evaluating the fluctuation contributions, we need to treat carefully the linear terms in the external sources and the induced perturbations. These contributions from the mesonic fluctuations are expected to have significant effects on the transport properties of hot and dense matter around the chiral phase transition or crossover.
Comments:
30 pages, 7 figures, submitted to Chinese Physics C!
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.05863 [pdf]
CPC(2019)·1 citation
06
[Submitted on 16 Sept 2018]
Susceptibilities of strongly interacting matter in a finite volume
Christian Spieles🇩🇪 · Marcus Bleicher🇩🇪 · Carsten Greiner🇩🇪
We investigate possible finite-volume effects on baryon number susceptibilities of strongly interacting matter. Assuming that a hadronic and a deconfined phase both contribute to the thermodynamic state of a finite system due to fluctuations, it is found that the resulting shapes of the net-baryon number distributions deviate significantly from the infinite volume limit for a given temperature $T$ and baryochemical potential $μ_{B}$ . In particular, the constraint on color-singletness for the finite quark-gluon phase contribution leads to a change of the temperature dependence of the susceptibilities in finite volumes. According to the model, the finite-volume effect depends qualitatively on the value of $μ_{B}$ .
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.05875 [pdf]
J.Phys.G(2019)·4 citations
07
[Submitted on 16 Sept 2018]
Effects of entrance channels on the deexcitation properties of the same compound nucleus formed by different pairs of collision partners
G. Mandaglio · A. Anastasi · F. Curciarello · G. Fazio · G. Giardina · A.K. Nasirov
The properties of deexcitation of the same $^{220}$ Th compound nucleus (CN) formed by different mass (charge) asymmetric reactions are investigated. It is demonstrated that the effective fission barrier $< B_{fis} >$ value being a function of the excitation energy $E_{CN}^{*}$ is strongly sensitive to the various orbital angular momentum $L = ℓ ℏ$ distributions of CN formed with the same excitation energy $E_{C N}^{*}$ by the very different entrance channels $^{16}$ O+ $^{204}$ Pb, $^{40}$ Ar+ $^{180}$ Hf, $^{82}$ Se+ $^{138}$ Ba and $^{96}$ Zr+ $^{124}$ Sn. Consequently, the competition between the fission and evaporation of light particles (neutron, proton, and $α$ -particle) processes along the deexcitation cascade of CN depends on the orbital angular momentum distribution of CN. Therefore, the ratio between the evaporation residue cross sections obtained after emission of neutral and charged particles and neutrons only for the same CN with a given excitation energy $E_{C N}^{*}$ is sensitive to the mass (charge) asymmetry of reactants in the entrance channel.
Comments:
9 pages, 6 figures, 2 tables, Accepted for publication on Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.05927 [pdf]
PRC(2018)·8 citations
08
[Submitted on 17 Sept 2018]
Breaking and restoration of rotational symmetry in the low-energy spectrum of light alpha-conjugate nuclei on the lattice I: $^{8} Be$ and $^{12} C$
G. Stellin🇩🇪 · S. Elhatisari🇩🇪 · U.-G. Meißner🇩🇪
The breaking of rotational symmetry on the lattice for bound eigenstates of the two lightest alpha conjugate nuclei is explored. Moreover, a macroscopic alpha-cluster model is used for investigating the general problems associated with the representation of a physical many-body problem on a cubic lattice. In view of the descent from the 3D rotation group to the cubic group symmetry, the role of the squared total angular momentum operator in the classification of the lattice eigenstates in terms of SO(3) irreps is discussed. In particular, the behaviour of the average values of the latter operator, the Hamiltonian and the inter-particle distance as a function of lattice spacing and size is studied by considering the $0^{+}$ , $2^{+}$ , $4^{+}$ and $6^{+}$ (artificial) bound states of $^{8} Be$ and the lowest $0^{+}$ , $2^{+}$ and $3^{-}$ multiplets of $^{12} C$ .
Comments:
Submitted to the European Physical Journal A, ID: EPJA-104750
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.06109 [pdf]
EPJA(2018)·8 citations
09
[Submitted on 17 Sept 2018]
Microscopic self-consistent description of induced fission dynamics: finite temperature effects
Jie Zhao · Tamara Nikšić · Dario Vretenar · Shan-Gui Zhou
The dynamics of induced fission of $^{226}$ Th is investigated in a theoretical framework based on the finite-temperature time-dependent generator coordinate method (TDGCM) in the Gaussian overlap approximation (GOA). The thermodynamical collective potential and inertia tensor at temperatures in the interval $T = 0 - 1.25$ MeV are calculated using the self-consistent multidimensionally constrained relativistic mean field (MDC-RMF) model, based on the energy density functional DD-PC1. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. Constrained RMF+BCS calculations are carried out in the collective space of axially symmetric quadrupole and octupole deformations for the asymmetric fissioning nucleus $^{226}$ Th. The collective Hamiltonian is determined by the temperature-dependent free energy surface and perturbative cranking inertia tensor, and the TDGCM+GOA is used to propagate the initial collective state in time. The resulting charge and mass fragment distributions are analyzed as functions of the internal excitation energy. The model can qualitatively reproduce the empirical triple-humped structure of the fission charge and mass distributions already at $T = 0$ , but the precise experimental position of the asymmetric peaks and the symmetric-fission yield can only be accurately reproduced when the potential and inertia tensor of the collective Hamiltonian are determined at finite temperature, in this particular case between $T = 0.75$ MeV and $T = 1$ MeV.
Comments:
9 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.06144 [pdf]
PRC(2019)·56 citations
10
[Submitted on 17 Sept 2018]
Aspects of approximation in modelling of the symmetry energy
Ilona Bednarek🇵🇱 · Monika Pienkos🇵🇱 · Jan Sladkowski🇵🇱 · Jacek Syska🇵🇱
Quality of approximations is an important issue in modelling nuclear matter. It is shown that the Padé approximation provides a useful tool for describing the symmetry energy in highly asymmetric systems. The focus is on the symmetry energy constraints. Some implications of the obtained results for astrophysics are also discussed.
Comments:
25 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1809.06203 [pdf]
J. Phys. Soc. Jpn. - Vol. 88, no. 12 (201…·4 citations
11
[Submitted on 17 Sept 2018]
Few-body universality in the deuteron-alpha system
Jin Lei🇺🇸 · L. Hlophe🇺🇸 · Ch. Elster🇺🇸 · A. Nogga🇩🇪 · F.M. Nunes🇺🇸 · D.R. Phillips🇺🇸
We treat $^{6}$ Li as an effective three-body ( $n$ - $p$ - $α$ ) system and compute the $d$ - $α$ $S -$ wave scattering length and three-body separation energy of $^{6}$ Li for a wide variety of nucleon-nucleon and $α$ -nucleon potentials which have the same (or nearly the same) phase shifts. The Coulomb interaction in the $p$ - $α$ subsystem is omitted. The results of all calculations lie on a one-parameter curve in the plane defined by the $d$ - $α$ $S -$ wave scattering length and the amount by which $^{6}$ Li is bound with respect to the $n$ - $p$ - $α$ threshold. We argue that these aspects of the $n$ - $p$ - $α$ system can be understood using few-body universality and that $^{6}$ Li can thus usefully be thought of as a two-nucleon halo nucleus.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1809.06351 [pdf]
PRC(2018)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE