Nuclear Theory·nucl-th

Friday·April 10, 2015

9 papers—4 primary·5 cross-listed

01
Pre-equilibrium evolution effects on heavy-ion collision observables
Jia Liu🇺🇸 · Chun Shen🇨🇦 · Ulrich W. Heinz🇺🇸
In order to investigate the importance of pre-equilibrium dynamics on relativistic heavy-ion collision observables, we match a highly non-equilibrium early evolution stage, modeled by free-streaming partons generated from the Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) and Monte Carlo Glauber (MC-Glb) models, to a locally approximately thermalized later evolution stage described by viscous hydrodynamics, and study the dependence of final hadronic transverse momentum distributions, in particular their underlying radial and anisotropic flows, on the switching time between these stages. Performing a 3-parameter fit of the measured values for the average transverse momenta $⟨ p_{⊥} ⟩$ for pions, kaons and protons as well as the elliptic and triangular flows of charged hadrons $v_{2, 3}^{ch}$ , with the switching time $τ_{s}$ , the specific shear viscosity $η / s$ during the hydrodynamic stage, and the kinetic decoupling temperature $T_{dec}$ as free parameters, we find that the preferred "thermalization" times $τ_{s}$ depend strongly on the model of the initial conditions. MC-KLN initial conditions require an earlier transition to hydrodynamic behavior (at $τ_{s} \approx$ 0.13 fm/ $c$ ) , followed by hydrodynamic evolution with a larger specific shear viscosity $η / s \approx$ 0.2, than MC-Glb initial conditions which prefer switching at a later time ( $τ_{s} \approx$ 0.6 fm/ $c$ ) followed by a less viscous hydrodynamic evolution with $η / s \approx$ 0.16. These new results including pre-equilibrium evolution are compared to fits without a pre-equilbrium stage where all dynamic evolution before the onset of hydrodynamic behavior is ignored. In each case, the quality of the dynamical descriptions for the optimized parameter sets, as well as the observables which show the strongest constraining power for the thermalization time, are discussed.
nucl-thPRC(2015)·124 citations
02
Adiabatic hyperspherical approach to large-scale nuclear dynamics
Yasuyuki Suzuki
We formulate a fully microscopic approach to large-scale nuclear dynamics using a hyperradius as a collective coordinate. An adiabatic potential is defined by taking account of all possible configurations at a fixed hyperradius, and its hyperradius dependence plays a key role in governing the global nuclear motion. In order to go to larger systems beyond few-body systems, we suggest basis functions of a microscopic multicluster model, propose a method for calculating matrix elements of an adiabatic Hamiltonian with use of Fourier transforms, and test its effectiveness.
nucl-thPTEP(2015)·5 citations
03
Constraints on neutron skin thickness in 208Pb and density-dependent symmetry energy
Jianmin Dong · Wei Zuo · Jianzhong Gu
Accurate knowledge about the neutron skin thickness $Δ R_{n p}$ in $^{208}$ Pb has far-reaching implications for different communities of nuclear physics and astrophysics. Yet, the novel Lead Radius Experiment (PREX) did not yield stringent constraint on the $Δ R_{n p}$ recently. We employ a more practicable strategy currently to probe the neutron skin thickness of $^{208}$ Pb based on a high linear correlation between the $Δ R_{n p}$ and $J - a_{sym}$ , where $J$ and $a_{sym}$ are the symmetry energy (coefficient) of nuclear matter at saturation density and of $^{208}$ Pb. An accurate $J - a_{sym}$ thus places a strong constraint on the $Δ R_{n p}$ . Compared with the parity-violating asymmetry $A_{PV}$ in the PREX, the reliably experimental information on the $J - a_{sym}$ is much more easily available attributed to a wealth of measured data on nuclear masses and on decay energies. The density dependence of the symmetry energy is also well constrained with the $J - a_{sym}$ . Finally, with a `tomoscan' method, we find that one just needs to measure the nucleon densities in $^{208}$ Pb starting from $R_{m} = 7.61 \pm 0.04$ fm to obtain the $Δ R_{n p}$ in hadron scattering experiments, regardless of its interior profile that is hampered by the strong absorption.
nucl-thPRC(2015)·19 citations
04
{\alpha}-accompanied cold ternary fission of $^{238 - 244}$ Pu isotopes in equatorial and collinear configuration
K. P. Santhosh · Sreejith Krishnan · B. Priyanka
The cold ternary fission of $^{238}$ Pu, $^{240}$ Pu, $^{242}$ Pu and $^{244}$ Pu isotopes, with $^{4}$ He as light charged particle, in equatorial and collinear configuration has been studied within the Unified ternary fission model (UTFM). The fragment combination $^{100}$ Zr+ $^{4}$ He+ $^{134}$ Te possessing the near doubly magic nuclei $^{134}$ Te (N=82, Z=52) gives the highest yield in the alpha accompanied ternary fission of $^{238}$ Pu. For the alpha accompanied ternary fission of $^{240}$ Pu, $^{242}$ Pu and $^{244}$ Pu isotopes, the highest yield was found for the fragment combination with doubly magic nuclei $^{132}$ Sn (N=82, Z=50) as the heavier fragment. The deformation and orientation of fragments have also been taken into account for the alpha accompanied ternary fission of $^{238 - 244}$ Pu isotopes, and it has been found that in addition to closed shell effect, ground state deformation also plays an important role in determining the isotopic yield in the ternary fission process. The emission probability and kinetic energy of long range alpha particles have been calculated and are found to be in good agreement with the experimental data.
nucl-thPRC(2015)·20 citations

Affiliations

first authorsco-authorsvia INSPIRE

Pre-equilibrium evolution effects on heavy-ion collision observables

Adiabatic hyperspherical approach to large-scale nuclear dynamics

Constraints on neutron skin thickness in 208Pb and density-dependent symmetry energy

{\alpha}-accompanied cold ternary fission of 238−244Pu isotopes in equatorial and collinear configuration

Affiliations

{\alpha}-accompanied cold ternary fission of $^{238 - 244}$ Pu isotopes in equatorial and collinear configuration