Nuclear Theory·nucl-th

Monday·January 30, 2017

9 papers—6 primary·3 cross-listed

01
Effect of tetrahedral shapes in heavy and superheavy nuclei
P.Jachimowicz · M. Kowal · J. Skalski
We search for effects of tetrahedral deformation $β_{32}$ over a range of $\sim 3000$ heavy and superheavy nuclei, $82 \leq Z \leq 126$ , using a microscopic-macroscopic model based on the deformed Woods-Saxon potential, well tested in the region. We look for the energy minima with a non-zero tetrahedral distortion, both absolute and conditional - with the quadrupole distortion constrained to zero. In order to assure reliability of our results we include 10 most important deformation parameters in the energy minimization. We could not find any cases of stable tetrahedral shapes. The only sizable - up to 0.7 MeV - lowering of the ground state occurs in superheavy nuclei $Z \geq 120$ for $N = 173 - 188$ , as a result of a {\it combined} action of two octupole deformations: $β_{32}$ and $β_{30}$ , in the ratio $β_{32} / β_{30} \approx 3/5$ . The resulting shapes are moderately oblate, with the superimposed distortion $β_{33}$ {\it with respect to the oblate axis}, which makes the equator of the oblate spheroid slightly triangular. Almost all found conditional minima are excited and not protected by any barrier, a handful of them are degenerate with the axial minima.
nucl-thPRC(2017)·25 citations
02
Full jet in quark-gluon plasma with hydrodynamic medium response
Yasuki Tachibana🇨🇳 · Ning-Bo Chang🇨🇳 · Guang-You Qin🇨🇳
We study the nuclear modifications of full jets and their structures in relativistic heavy-ion collisions including the effect of hydrodynamic medium response to jet quenching. To study the evolutions of the full jet shower and the traversed medium with energy and momentum exchanges between them, we formulate a coupled jet-fluid model consisting of a set of jet transport equations and relativistic hydrodynamics equations with source terms. In our model, the full jet shower interacts with the medium and gets modified via collisional and radiative processes during the propagation. Meanwhile, the energy and momentum are deposited from the jet shower to the medium and then evolve with the medium hydrodynamically. The full jet defined by a cone size in the final state includes the jet shower and the particles produced from jet-induced flow. We apply our model to calculate the full jet energy loss and the nuclear modifications of jet rate and shape in Pb+Pb collisions at $2.76 A TeV$ . It is found that the inclusion of jet-induced flow contribution leads to stronger jet-cone size dependence for jet energy loss and jet suppression. Jet-induced flow also has a significant contribution to jet shape function and dominates at large angles away from the jet axis.
nucl-thhep-exhep-phnucl-exPRC(2017)·164 citations
03
Binding energies and pairing gaps in semi-magic nuclei obtained using new regularized higher-order EDF generators
K. Bennaceur🇫🇷 · J. Dobaczewski🇫🇮 · Y. Gao🇨🇳
We present results of the Hartree-Fock-Bogolyubov calculations performed using nuclear energy density functionals based on regularized functional generators at next-to-leading and next-to-next-to-leading order. We discuss properties of binding energies and pairing gaps determined in semi-magic spherical nuclei. The results are compared with benchmark calculations performed for the functional generator SLyMR0 and functional UNEDF0.
nucl-th3 citations
04
Cooper pairs in the Borromean nuclei $^{6}$ He and $^{11}$ Li using continuum single particle level density
R. M. Id Betan
A Borromean nucleus is a bound three-body system which is pairwise unbound because none of the two-body subsystem interactions are strong enough to bind them in pairs. As a consequence, the single-particle spectrum of a neutron in the core of a Borromean nucleus is purely continuum, similarly to the spectrum of a free neutron, but two valence neutrons are bound up in such a core. Most of the usual approaches do not use the true continuum to solve the three-body problem but use a discrete basis, like for example, wave functions in a finite box. In this paper the proper continuum is used to solve the pairing Hamiltonian in the continuum spectrum of energy by using the single particle level density devoid of the free gas. It is shown that the density defined in this way modulates the pairing in the continuum. The partial-wave occupation probabilities for the Borromean nuclei $^{6}$ He and $^{11}$ Li are calculated as a function of the pairing strength. While at the threshold strength the $(s_{1/2})^{2}$ and $(p_{3/2})^{2}$ configurations are equally important in $^{6}$ He, the $(s_{1/2})^{2}$ configuration is the main one in $^{11}$ Li. For very small strength the $(s_{1/2})^{2}$ configuration becomes the dominant in both Borromean nuclei. At the physical strength, the calculated wave function amplitudes show a good agreement with other methods and experimental data which indicates that this simple model grasps the essence of the pairing in the continuum.
nucl-thNPA(2017)·8 citations
05
Irreducible 3-body forces contributions to the self-energy
F. Raimondi · C. Barbieri
The inclusion of the three-nucleon forces (3NFs) in \textit{ab initio} many-body approaches is a formidable task, due to the computational load implied by the treatment of their matrix elements. For this reason, practical applications have mostly been limited to contributions where 3NFs enter as effective two-nucleon interactions. In this contribution, we derive the algebraic diagrammatic construction (ADC) working equations for a specific Feynman diagram of the self-energy that contains a fully irreducible three-nucleon force. This diagram is expected to be the most important among those previously neglected, because it connects dominant excited intermediate state configurations.
nucl-th1 citation
06
Surface tension of compressed, superheavy atoms
Jorge A. Rueda · Yuan-Bin Wu · She-Sheng Xue
Based on the relativistic mean field theory and the Thomas-Fermi approximation, we study the surface properties of compressed, superheavy atoms. By compressed, superheavy atom we mean an atom composed by a superheavy nuclear core (superheavy nucleus) with mass number of the order of $1 0^{4}$ , and degenerate electrons that neutralize the system. Some electrons penetrate into the superheavy nuclear core and the rest surround it up to a distance that depends upon the compression level. Taking into account the strong, weak, and electromagnetic interactions, we numerically study the structure of compressed, superheavy atoms and calculate the nuclear surface tension and Coulomb energy. We analyze the influence of the electron component and the background matter on the nuclear surface tension and Coulomb energy of compressed, superheavy atoms. We also compare and contrast these results in the case of compressed, superheavy atoms with phenomenological results in nuclear physics and the results of the core-crust interface of neutron stars with global charge neutrality. Based on the numerical results we study the instability against Bohr-Wheeler surface deformations in the case of compressed, superheavy atoms. The results in this article show the possibility of the existence of such compressed, superheavy atoms, and provide the evidence of strong effects of the electromagnetic interaction and electrons on the structure of compressed, superheavy atoms.
nucl-thastro-ph.HEastro-ph.SR1 citation
07
Collinear parton distributions and the structure of the nucleon sea in a light-front meson-cloud model
S. Kofler (Graz U.)🇦🇹 · B. Pasquini (Pavia U. & INFN, Pavia)🇮🇹
The unpolarized, helicity and transversity parton distribution functions of the nucleon are studied within a convolution model where the bare nucleon is dressed by its virtual meson cloud. Using light-front time-ordered perturbation theory, the Fock states of the physical nucleon are expanded in a series involving a bare nucleon and two-particle, meson-baryon, states. The bare baryons and mesons are described with light-front wave functions (LFWFs) for the corresponding valence-parton components. Using a representation in terms of overlap of LFWFs, the role of the non-perturbative antiquark degrees of freedom and the valence quark contribution at the input scale of the model is discussed for the leading-twist collinear parton distributions. After introducing perturbative QCD effects through evolution to experimental scales, the results are compared with available data and phenomenological extractions. Predictions for the nucleon tensor charge are also presented, finding a very good agreement with recent phenomenological extractions.
↳ hep-phnucl-thPRD(2017)·15 citations
08
Heavy neutrino potential for neutrinoless double beta decay
Yoritaka Iwata🇯🇵
Heavy neutrino potential for neutrinoless double beta decay is studied with focusing on its statistical property. The existence condition for heavy neutrinos is also presented. In particular sterile neutrinos are possible candidate for heavy nuetrinos. The statistics provide a gross view of understanding amplitude of constitutional components of the nuclear matrix element.
↳ hep-phnucl-thPoS(2017)·1 citation
09
Top-quark and Higgs boson perspectives at heavy-ion colliders
David d'Enterria🇨🇭
The perspectives for measuring the top quark and the Higgs boson in nuclear collisions at the LHC and Future Circular Collider (FCC) are summarized. Perturbative QCD calculations at (N)NLO accuracy, including nuclear parton distribution functions, are used to determine their cross sections and visible yields after standard analysis cuts in PbPb and pPb collisions at the LHC ( $s_{N N}$ = 5.5, 8.8 TeV) and FCC ( $s_{N N}$ = 39, 63 TeV). In their "cleanest" decay channels, $t t ˉ \to b b ˉ 2 ℓ 2 ν$ and $H \to γ γ, 4 ℓ$ , about 10 $^{3}$ ( $1 0^{5}$ ) top-quark and 10 (10 $^{3}$ ) Higgs-boson events are expected at the LHC (FCC) for their total nominal integrated luminosities. Whereas the $t t ˉ$ observation is clearcut at both colliders, evidence for Higgs production, perfectly possible at the FCC, requires integrating $\times$ 30 more luminosities at the LHC.
↳ hep-exhep-phnucl-exnucl-thNucl.Part.Phys.Proc.(2017)·18 citations

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first authorsco-authorsvia INSPIRE