Nuclear Theory·nucl-th

Friday·July 26, 2019

13 papers—8 primary·5 cross-listed

01
[Submitted on 24 Jul 2019]
Relaxation Time for Strange Quark Spin in Rotating Quark-Gluon Plasma
Joseph I. Kapusta🇺🇸 · Ermal Rrapaj🇺🇸 · Serge Rudaz🇺🇸
Experiments at the Relativistic Heavy Ion Collider (RHIC) have measured the net polarization of $Λ$ and $Λ ˉ$ hyperons and attributed it to a coupling between their spin and the vorticity of the fluid created in heavy ion collisions. Equipartition of energy is generally assumed, but the dynamical mechanism which polarizes them has yet to be determined. We consider two such mechanisms: vorticity fluctuations and helicity flip in scatterings between strange quarks and light quarks and gluons. With reasonable parameters both mechanisms lead to equilibration times orders of magnitude too large to be relevant to heavy ion collisions. Our conclusion is that strange quark spin or helicity is unchanged from the time they are created to the time they hadronize. A corollary is that vorticity fluctuations do not affect the hyperon spin either.
Comments:
31 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th)
arXiv:
1907.10750 [pdf]
PRC(2020)·58 citations
02
[Submitted on 24 Jul 2019]
Underlying structure of collective bands and self-organization in quantum systems
Takaharu Otsuka · Yusuke Tsunoda · Takashi Abe · Noritaka Shimizu · Piet Van Duppen
The underlying structure of low-lying collective bands of atomic nuclei is discussed from a novel perspective on the interplay between single-particle and collective degrees of freedom, by utilizing state-of-the-art configuration interaction calculations on heavy nuclei. Besides the multipole components of the nucleon-nucleon interaction that drive collective modes forming those bands, the monopole component is shown to control the resistance against such modes. The calculated structure of 154Sm corresponds to coexistence between prolate and triaxial shapes, while that of 166Er exhibits a deformed shape with a strong triaxial instability. Both findings differ from traditional views based on beta/gamma vibrations. The formation of collective bands is shown to be facilitated from a self-organization mechanism.
Comments:
4 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1907.10759 [pdf]
PRL(2019)·66 citations
03
[Submitted on 25 Jul 2019]
Pseudorapidity dependent hydrodynamic response in heavy-ion collisions
Hui Li🇨🇳 · Li Yan🇨🇳
We propose a differential hydrodynamic response relation, $V_{2} (ζ) = \int d ξ G (ζ - ξ) E_{2} (ξ)$ , to describe the formation of a pseudorapidity dependent elliptic flow in heavy-ion collisions, in response to a fluctuating three-dimensional initial density profile. By analyzing the medium expansion using event-by-event simulations of 3+1D MUSIC, with initial conditions generated via the AMPT model, the differential response relation is verified. Given the response relation, we are able to separate the two-point correlation of elliptic flow in pseudorapidity into fluid response and two-point correlation of initial eccentricity. The fluid response contains information of the speed of sound and shear viscosity of the medium. From the pseudorapidity dependent response relation, a finite radius of convergence of hydrodynamic gradient expansion is obtained with respect to realistic fluids in heavy-ion collisions.
Comments:
The published version, 7 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1907.10854 [pdf]
PLB(2020)·11 citations
04
[Submitted on 25 Jul 2019]
Primordial fluctuations in heavy-ion collisions
François Gelis🇫🇷 · Giuliano Giacalone🇫🇷 · Pablo Guerrero-Rodríguez🇪🇸 · Cyrille Marquet🇫🇷 · Jean-Yves Ollitrault🇫🇷
We present a simple description of the energy density profile created in a nucleus-nucleus collision, motivated by high-energy QCD. The energy density is modeled as the sum of contributions coming from elementary collisions between localized charges and a smooth nucleus. Each of these interactions creates a sharply-peaked source of energy density falling off at large distances like $1/ r^{2}$ , corresponding to the two-dimensional Coulomb field of a point charge. Our model reproduces the one-point and two-point functions of the energy density field calculated in the framework of the color glass condensate effective theory, to leading logarithmic accuracy. We apply it to the description of eccentricity fluctuations. Unlike other existing models of initial conditions for heavy-ion collisions, it allows us to reproduce simultaneously the centrality dependence of elliptic and triangular flow.
Comments:
6 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1907.10948 [pdf]
21 citations
05
[Submitted on 25 Jul 2019]
Nucleon momentum distributions in asymmetric nuclear matter
Z. X. Yang🇨🇳 · X. L. Shang🇨🇳 · G. C. Yong🇨🇳 · W. Zuo🇨🇳 · Y. Gao🇨🇳
Nucleon momentum distributions at various densities and isospin-asymmetries for nuclear matter are investigated systematically within the extended Bruecker-Hartree-Fock approach.The shapes of the normalized momentum distributions varying with $k / k_{F}$ are practically identical, while the density and isospin dependent magnitude of the distribution is directly related to the depletion of the Fermi sea. Based on these properties, a parameterized formula is proposed with the parameters calibrated to the calculated result.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.10977 [pdf]
PRC(2019)·27 citations
06
[Submitted on 25 Jul 2019]
Neutron-proton pairing in Nuclear Matter
Xiao-Hua Fan · Xin-le Shang · Jian-Min Dong · Wei Zuo
The self-energy effect on the neutron-proton (np) pairing gap is investigated up to the third order within the framework of the extend Bruecker-Hartree-Fock (BHF) approach combined with the BCS theory. The self-energy up to the second-order contribution turns out to reduce strongly the effective energy gap, while the \emph{renormalization} term enhances it significantly. In addition, the effect of the three-body force on the np pairing gap is shown to be negligible. To connect the present results with the np pairing in finite nuclei, an effective density-dependent zero-range pairing force is established with the parameters calibrated to the microscopically calculated energy gap.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.10986 [pdf]
PRC(2019)·12 citations
07
[Submitted on 25 Jul 2019]
Macroscopic manifestations of rotating triaxial superfluid nuclei
P. Schuck🇫🇷 · M. Urban🇫🇷
Recently, Allmond and Wood [Phys. Lett. B 767, 226 (2017)] were able to extract the three moments of inertia $I_{k}$ of a dozen of superfluid triaxial nuclei from experimental data. The observed dependence of the $I_{k}$ on the deformation parameters is rather smooth. Here we show that these moments of inertia can be surprisingly well explained by a semiclassical cranked Hartree-Fock-Bogoliubov (HFB) calculation in which the velocity field is a simple superposition of rigid and irrotational flows.
Comments:
5 pages; v2: minor revision (pairing gaps from 5-point formula and improved figures)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.11008 [pdf]
PRC(2019)·8 citations
08
[Submitted on 25 Jul 2019]
Studies of quasiclassical approach applicability to true three-body decays
O.M. Sukhareva · L.V. Grigorenko · D.A. Kostyleva · M.V. Zhukov
Within the hyperspherical harmonics approach the three-body problem is reduced to a motion of one effective particle in a "strongly deformed" field, which is described in coupled-channel formalism. This method is especially suited to studies of phenomena characterized by genuine three-body dynamics, e.g. Borromean haloes and true three-body decays. The reduction of the hyperspherical equations set to a single-channel Schrödinger equation provides the basis for the use of the standard quasiclassical expression for calculations of widths for true three-body decays. We demonstrate that the quasiclassical approach by itself is quite precise in application to typical profiles of the three-body effective potentials. However, the reduction to single-channel formalism leads to significant overestimation of the two-proton width $Γ_{2 p}$ . This is demonstrated by the example of the $^{17}$ Ne first excited $3/ 2^{-}$ state decay, questioning, however, the applicability of such an approximation in general.
Comments:
12 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1907.11013 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE