Nuclear Theory·nucl-th

Wednesday·May 12, 2021

11 papers—4 primary·7 cross-listed

01
[Submitted on 10 May 2021]
Incoherent approximation for neutron up-scattering cross sections and its corrections for slow neutrons and low crystal temperatures
Stefan Döge🇩🇪 · Chen-Yu Liu🇺🇸 · Albert Young🇺🇸 · Christoph Morkel🇩🇪
The incoherent approximation (IA) is often used for calculating the one-phonon inelastic neutron scattering cross section for arbitrary solids. It is valid for thermal neutrons but for slow neutrons it requires a correction, which is significant for isotopes that are strong coherent scatterers. In this article, we present the extension of the Placzek--Van Hove corrections for slow neutrons in the limit of low temperatures using the example of solid \emph{ortho}-deuterium (sD $_{2}$ ). Our approach yields realistic one-phonon up-scattering cross sections for sD $_{2}$ and shows the IA to be a factor of 2 to 5 too high for ultracold neutron (UCN) up-scattering in sD $_{2}$ . Our calculations are compared with previously published Monte Carlo calculations of the one-phonon cross section based on the dynamic structure function $S (q, ω)$ of polycrystalline \emph{ortho}-deuterium and are found to be consistent with them. Furthermore, we provide the means for easily replicable calculations of the one-phonon up-scattering cross sections of solid \emph{ortho}-deuterium for slow neutrons. These should from now on be used in calculations and simulations of UCN scattering in sD $_{2}$ .
Comments:
6 pages, 1 figure, 1 table
Subjects:
Nuclear Theory (nucl-th); cond-mat.other (cond-mat.other)
arXiv:
2105.04624 [pdf]
PRC(2021)·4 citations
02
[Submitted on 10 May 2021]
Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817
Bao-An Li🇺🇸 · Bao-Jun Cai🇨🇳 · Wen-Jie Xie🇨🇳 · Nai-Bo Zhang🇨🇳
New observational data of neutron stars since GW170817 have helped improve our knowledge about nuclear symmetry energy especially at high densities. We have learned particularly: (1) The slope parameter $L$ of nuclear symmetry energy at saturation density $ρ_{0}$ of nuclear matter from 24 new analyses is about $L \approx 57.7 \pm 19$ MeV at 68\% confidence level consistent with its fiducial value, (2) The curvature $K_{sym}$ from 16 new analyses is about $K_{sym} \approx - 107 \pm 88$ MeV, (3) The magnitude of nuclear symmetry energy at $2 ρ_{0}$ , i.e. $E_{sym} (2 ρ_{0}) \approx 51 \pm 13$ MeV at 68\% confidence level, has been extracted from 9 new analyses of neutron star observables consistent with results from earlier analyses of heavy-ion reactions and the latest predictions of the state-of-the-art nuclear many-body theories, (4) while the available data from canonical neutron stars do not provide tight constraints on nuclear symmetry energy at densities above about $2 ρ_{0}$ , the lower radius boundary $R_{2.01} = 12.2$ km from NICER's very recent observation of PSR J0740+6620 of mass $2.08 \pm 0.07$ $M_{⊙}$ and radius $R = 12.2 - 16.3$ km at 68\% confidence level sets a tight lower limit for nuclear symmetry energy at densities above $2 ρ_{0}$ , (5) Bayesian inferences of nuclear symmetry energy using models encapsulating a first-order hadron-quark phase transition from observables of canonical neutron stars indicate that the phase transition shift appreciably both the $L$ and $K_{sym}$ to higher values but with larger uncertaintie , (6) The high-density behavior of nuclear symmetry energy affects significantly the minimum frequency necessary to rotationally support GW190814's secondary component of mass (2.50-2.67) $M_{⊙}$ as the fastest and most massive pulsar discovered so far.
Comments:
Published version with added discussions and references
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex)
arXiv:
2105.04629 [pdf]
Universe(2021)·229 citations
03
[Submitted on 11 May 2021]
Model investigations of the correlation between the mean transverse momentum and anisotropic flow in shape-engineered events
Niseem Magdy🇺🇸 · Roy A. Lacey🇺🇸
The correlation between the event mean-transverse momentum $[p_{T}]$ , and the anisotropic flow magnitude $v_{n}$ , $ρ (v_{n}^{2}, [p_{T}])$ , has been argued to be sensitive to the initial conditions in heavy-ion collisions. We use simulated events generated with the AMPT and EPOS models for Au+Au at $s_{N N}$ = 200 GeV, to investigate the model dependence and the response and sensitivity of the $ρ (v_{2}^{2}, [p_{T}])$ correlator to collision-system size and shape, and the viscosity of the matter produced in the collisions. We find good qualitative agreement between the correlators for the string melting version of the AMPT model and the EPOS model. The model investigations for shape-engineered events as well as events with different viscosity ( $η / s$ ), indicate that $ρ (v_{2}^{2}, [p_{T}])$ is sensitive to the initial-state geometry of the collision system but is insensitive to sizable changes in $η / s$ for the medium produced in the collisions. These findings suggest that precise differential measurements of $ρ (v_{2}^{2}, [p_{T}])$ as a function of system size, shape, and beam-energy could provide more stringent constraints to discern between initial-state models and hence, more reliable extractions of $η / s$ .
Comments:
8 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2105.04879 [pdf]
PLB(2021)·12 citations
04
[Submitted on 11 May 2021]
Pauli energy contribution to nucleus-nucleus interaction
A.S. Umar🇺🇸 · C. Simenel🇦🇺 · K. Godbey🇺🇸
Background: The Pauli exclusion principle plays a crucial role as a building block of many-body quantal systems comprised of fermions. It also induces a "Pauli repulsion" in the interaction between di-nuclear systems. It has been shown in [Phys. Rev. C 95, 031601 (2017)] that the Pauli repulsion widens the nucleus-nucleus potential barrier, thus hindering sub-barrier fusion. Purpose: To investigate the proton and neutron contributions to the Pauli repulsion, both in the bare potential neglecting shape polarization and transfer between the reactants, as well as in the dynamical potential obtained by accounting for such dynamical rearrangements. Methods: As the basis of our study we utilize the Pauli kinetic energy (PKE) obtained by studying the nuclear localization function (NLF). Recently this approach has been generalized to incorporate all of the dynamical and time-odd terms present in the nuclear energy density functional. This approach is employed in the DCFHF and DC-TDHF methods. Results: The PKE spatial distribution shows that a repulsion occurs in the neck between the nuclei when they first touch. Inside the barrier, neutrons can contribute significantly more to the Pauli repulsion in neutron-rich systems. Dynamical effects tend to lower the Pauli repulsion near the barrier. Proton and neutron dynamical contributions to the PKE significantly differ inside the barrier for asymmetric collisions, which is interpreted as an effect of multinucleon transfer. Conclusions: The PKE is shown to make a significant contribution to nuclear interaction potentials. Protons and neutrons can play very different roles in both the bare potential and in the dynamical rearrangement. Further microscopic studies are required to better understand the role of transfer and to investigate the effect of pairing and deformation.
Comments:
11 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2105.05245 [pdf]
PRC(2021)·21 citations

Affiliations

first authorsco-authorsvia INSPIRE

Incoherent approximation for neutron up-scattering cross sections and its corrections for slow neutrons and low crystal temperatures

Progress in Constraining Nuclear Symmetry Energy Using Neutron Star Observables Since GW170817

Model investigations of the correlation between the mean transverse momentum and anisotropic flow in shape-engineered events

Pauli energy contribution to nucleus-nucleus interaction

Affiliations