Nuclear Theory·nucl-th

Tuesday·November 27, 2018

18 papers—11 primary·7 cross-listed

01
From QCD Symmetries to Nuclei and Neutron Stars
Wolfram Weise🇩🇪
Global symmetries and symmetry breaking patterns of QCD with light quarks, in particular chiral symmetry, provide basic guidance not only for low-energy hadron physics but also for nuclear forces and the nuclear many-body problem. Recent developments of Chiral Effective Field Theory applications to nuclear and neutron matter are summarized, with special emphasis on a (non-perturbative) extension using functional renormalisation group methods. Topics include: nuclear thermodynamics, extrapolations to dense baryonic matter and constraints from neutron star observables.
nucl-thIJMPE(2018)·5 citations
02
Fission of super-heavy nuclei: Fragment mass distributions and their dependence on excitation energy
N. Carjan · F.A. Ivanyuk · Yu.Ts. Oganessian
The mass and total kinetic energy distributions of the fission fragments in the fission of even-even isotopes of superheavy elements from Hs (Z=108) to Og (Z=118) are estimated using a pre-scission point model. We restrict to nuclei for which spontaneous fission has been experimentally observed. The potential energy surfaces are calculated with Strutinsky's shell correction procedure. The parametrization of the nuclear shapes is based on Cassini ovals. For the just before scission configuration we fix $α$ =0.98, what corresponds to $r_{n ec k} \approx 2$ fm, and take into account another four deformation parameters: $α_{1}, α_{3}, α_{4}, α_{6}$ . The fragment-mass distributions are estimated supposing they are due to thermal fluctuations in the mass asymmetry degree of freedom just before scission. The influence of the excitation energy of the fissioning system on these distributions is studied. The distributions of the total kinetic energy (TKE) of the fragments are also calculated (in the point-charge approximation). In Hs, Ds and Cn isotopes a transition from symmetric to asymmetric fission is predicted with increasing neutron number N (at N $\approx$ 168). Super-symmetric fission ocurs at N $\approx$ 160. When the excitation energy increases from 0 to 30 MeV, the peaks (one or two) of the mass distributions become only slightly wider. The first two moments of the TKE distributions are displayed as a function of the mass number A of the fissioning nucleus. A slow decrease of the average energy and a minimum of the width (at N $\approx$ 162) is found.
nucl-thPRC(2019)·22 citations
03
Probing cold nuclear matter effects with the productions of isolated- $γ$ and $γ$ +jet in p $+$ Pb collisions at $s_{N N} =$ 8.16 TeV
Guo-Yang Ma🇨🇳 · Wei Dai🇨🇳 · Ben-Wei Zhang🇨🇳
We investigate the cold nuclear matter (CNM) effects on the productions of the isolated prompt photon and $γ +$ jet in proton-lead collisions at $8.16$ TeV under the next-to-leading order (NLO) perturbative quantum chromodynamics calculations with four parametrizations for nuclear parton distribution functions (nPDFs), i.e. DSSZ, EPPS16, nCTEQ15, nIMParton. Our theoretical calculations provide good descriptions of pp baseline in the ATLAS collaboration and make predictions for future experimental results at $p$ + $Pb$ collisions. We calculate the dependence of the nuclear modification factor of isolated prompt photon on transverse momentum $p_{T}^{γ}$ and pseudo-rapidity $η^{γ}$ at very forward and backward rapidity regions, and demonstrate that the forward-to-backward yield asymmetries $Y_{pPb}^{asym}$ as a function of $p_{T}^{γ}$ with different nPDFs parametrizations have diverse behaviors. Furthermore, the nuclear modification factor of isolated- $γ +$ jet $R_{pPb}^{γ Jet}$ as a function of $γ +$ jet's pseudo-rapidity $η_{γ Jet} = \frac{1}{2} (η_{γ} + η_{Jet})$ at different average transverse momentum $p_{T}^{avg} = \frac{1}{2} (p_{T}^{γ} + p_{T}^{Jet})$ has been discussed, which can facilitate a tomography study of CNM effects with precise locations in a rather wide kinematic region by varying the transverse momenta and rapidities of both isolated photon and jet in p+A collisions.
nucl-thCPC(2019)·3 citations
04
Lifetime estimations from RHIC Au+Au data
Gábor Kasza🇭🇺 · Tamás Csörgő🇭🇺
We discuss a recently found family of exact and analytic, finite and accelerating, 1+1 dimensional solutions of perfect fluid relativistic hydrodynamics to describe the pseudorapidity densities and longitudinal HBT-radii and to estimate the lifetime parameter and the initial energy density of the expanding fireball in Au+Au collisions at RHIC with $s_{N N} = 130$ GeV and $200$ GeV colliding energies. From these exact solutions of relativistic hydrodynamics, we derive a simple and powerful formula to describe the pseudorapidity density distributions in high energy proton-proton and heavy ion collisions, and derive the scaling of the longitudinal HBT radius parameter as a function of the pseudorapidity density. We improve upon several oversimplifications in Bjorken's famous initial energy density estimate, and apply our results to estimate the initial energy densities of high energy reactions with data-driven pseudorapidity distributions. When compared to similar estimates at the LHC energies, our results indicate a surprising and non-monotonic dependence of the initial energy density on the energy of heavy ion collisions.
nucl-thInt.J.Mod.Phys.A(2019)·15 citations
05
Topology change and nuclear symmetry energy in compact-star matter
Xiang-Hai Liu🇨🇳 · Yong-Liang Ma🇨🇳 · Mannque Rho🇫🇷
We show that the cusp-like structure in the nuclear symmetry energy, a consequence of topology change, visible in the skyrmion lattice description of dense matter is extremely robust. It is present in the Skyrme model -- with the pion field only -- and is left unscathed by massive degrees of freedom such as the vector mesons $ρ$ and $ω$ and also the scalar meson introduced as a dilaton. It leads to the emergence of parity-doubling at the skyrmion-half-skyrmion transition and impacts on the nuclear symmetry energy "wilderness" landscape, weeding out roughly half of the wilderness. It is shown that a pseudo-conformal sound velocity arises at a precocious density at which the cusp is formed. It is suggested that the topology change, being robust, could impact on the tidal deformability observed in gravity waves
nucl-thhep-phPRC(2019)·8 citations
06
$α$ Clustering slightly above $^{100}$ Sn in the Light of the New Experimental Data on the Superallowed $α$ Decay
Dong Bai🇨🇳 · Zhongzhou Ren🇨🇳
The recently observed $α$ -decay chain $^{108} Xe \to^{104} Te \to^{100} Sn$ [K.~Auranen \emph{et al.}, Phys.\ Rev.\ Lett.\ {\bf121}, 182501 (2018)] could provide valuable information on the $α$ clustering in even-even nuclei slightly above the major shells $Z = 50$ and $N = 50$ . In this work, this $α$ -decay chain is studied theoretically within the framework of the density-dependent cluster model plus the two-potential approach. We calculate the $α$ -decay half-lives of $^{104}$ Te and $^{108}$ Xe and study in detail their dependence on the $Q$ value and the density-profile parameters of the core nucleus. Various physical properties of $^{104}$ Te, the heaviest nucleus with a doubly magic self-conjugate core $+$ $α$ , are calculated, with two different assumptions on the renormalization factor of the double-folding potential, which could be a useful reference for future experimental studies.
nucl-thEPJA(2018)·21 citations
07
Local meson-baryon coupled-channels potential for the Lambda(1405)
Kenta Miyahara🇯🇵 · Tetsuo Hyodo🇯🇵 · Wolfram Weise🇩🇪
A local coupled-channels Kbar N-pi Sigma-pi Lambda potential is constructed, equivalently reproducing the scattering amplitude in chiral SU(3) dynamics. By analyzing the wave function of the Lambda(1405), we show the Kbar N dominance of the upper pole within the two-pole structure of the Lambda(1405). The resulting potential will be useful for investigating Kbar few-nucleon systems including their coupled channels.
nucl-thhep-ph0 citations
08
Sensitivity of nuclear statistical equilibrium to nuclear uncertainties during stellar core collapse
Shun Furusawa
I have systematically investigated the equations of state (EOSs) in nuclear statistical equilibrium under thermodynamic conditions relevant for core collapse of massive stars by varying the bulk properties of nuclear matter, the mass data for neutron-rich nuclei, and the finite-temperature modifications of the nuclear model. It is found that the temperature dependence of the nuclear free energies has a significant impact on the entropy and nuclear composition, which affect the dynamics of core-collapse supernovae. There is a little influence from the bulk properties and the mass data. For all models, common nuclei that are likely to contribute to core-deleptonization are those near $Z \approx 30$ and $N \approx 50$ . A model with a semi-empirical expression for internal degrees of freedom, however, overestimates the number densities of magic nuclei with $N \approx 50$ and $82$ , while a model, in which nuclear shell effects are not considered, underestimates the number densities of heavy nuclei, and especially of the magic nuclei. Other models, which include the temperature dependence of shell effects in the internal degrees of freedom and/or in the nuclear internal free energy, indicate that the difference in population between magic nuclei and non-magic nuclei disappears as the temperature increases. The construction of complete statistical EOS will require further theoretical and experimental studies of medium-mass, neutron-rich nuclei with proton numbers 25-45 and neutron numbers 40-85.
nucl-thastro-ph.HEastro-ph.SRPRC(2018)·9 citations
09
Coexistence of Anderson-Bogoliubov phonon and quadrupole cluster vibration in neutron star inner crust
Tsenenori Inakura🇯🇵 · Masayuki Matsuo🇯🇵
Background: Low-lying collective excitations of inner crust matter in neutron stars are expected to have impact on observables such as the quasi-periodic oscillation in giant flares and the cooling of inner crust in transient phenomena. Coupling between Anderson-Bogoliubov superfluid phonon (AB phonon) in superfluid neutron gas and collective excitations of nuclear clusters is a key issue. Purpose: We intend to predict the nature of low-lying excitation modes of superfluid inner crust matter with focus on quadrupole excitations around a spherical nuclear cluster. We study how the AB phonon of neutron superfluid and possible quadrupole shape vibration of clusters are affected by the inhomogeneous structure of inner crust matter. Results: The calculated results indicate emergence of both AB phonon and quadrupole shape vibration of the cluster with small mixing between the two collective modes. The quadruple AB phonon is similar to that in uniform superfluid apart from small admixture of the shape vibration of cluster. The excitation energy and the collectivity of the cluster vibration mode shows strong and oscillatory dependence on the neutron chemical potential (the neutron gas density), leading to softening and instability in certain situations. This is caused by the resonance shell effect where unbound but resonant single-particle states of neutrons play a central role. Conclusions: The AB phonon of superfluid neutron gas and the quadrupole shape vibration of nuclear cluster coexist in inner crust. The coupling between the AB phonon and the quadrupole shape vibration is weak. The collectivity of the quadrupole shape vibration is governed by the resonance shell effect, and it suggests that emergence of deformed nuclear clusters is possible at any layer of inner crust.
nucl-thPRC(2019)·9 citations
10
Fluctuating shapes of the fireballs in heavy-ion collisions
Boris Tomasik🇸🇰 · Jakub Cimerman🇨🇿 · Renata Kopecna🇩🇪 · Martin Schulc🇨🇿
We argue that energy and momentum deposition from hard partons into quark-gluon plasma induces an important contribution to the final state hadron anisotropies. We also advocate a novel method of Event Shape Sorting which allow to analyse the azimuthal anisotropies of the fireball dynamics in more detail. A use of the method in femtoscopy is demonstrated.
nucl-thhep-exhep-phEPJ Web Conf.(2019)·1 citation
11
A geometrical interpretation of the Thomas theorem and the Efimov States
H. Zheng · A. Bonasera
Using a generalized Bohr model and the hyper-spherical formalism for a three-body system, we derive the Thomas theorem assuming a simple interaction depending on the range of the potential. We discuss the conditions for which an unbound two-body system produces a bound three-body system and derive universal energy functions. We apply our model to $^{4}$ He and Triton atoms as well as to the triton nucleus. Using their scattering lengths and effective ranges, we are able to reproduce the two-body or the three-body binding energies with only one parameter fitted. Prediction for excited (Efimov) levels are also given and in particular we demonstrate that for some hyper-angles two equal minima appear which indicate a phase (shape) transition similar to the Landau's theory of phase transition. We suggest that the observed excited levels in two different experiments for the triton nucleus are indeed Efimov levels and there may be more surprises.
nucl-thphysics.atom-phJ.Phys.Comm.(2020)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE