Nuclear Theory·nucl-th

Wednesday·February 14, 2018

8 papers—3 primary·5 cross-listed

01
$β$ -delayed fission in $r$ -process nucleosynthesis
M. R. Mumpower · T. Kawano · T. M. Sprouse · N. Vassh · E. M. Holmbeck · R. Surman · P. Moller
We present $β$ -delayed neutron emission and $β$ -delayed fission calculations for heavy, neutron-rich nuclei using the coupled Quasi-Particle Random Phase Approximation plus Hauser-Feshbach (QRPA+HF) approach. From the initial population of a compound nucleus after $β$ -decay, we follow the statistical decay taking into account competition between neutrons, $γ$ -rays, and fission. We find a region of the chart of nuclides where the probability of $β$ -delayed fission is $\sim 100$ %, that likely prevents the production of superheavy elements in nature. For a subset of nuclei near the neutron dripline, neutron multiplicity and the probability of fission are both large, leading to the intriguing possibility of multi-chance $β$ -delayed fission, a new decay mode for extremely neutron-rich heavy nuclei. In this new decay mode, $β$ -decay can be followed by multiple neutron emission leading to subsequent daughter generations which each have a probability to fission. We explore the impact of $β$ -delayed fission in rapid neutron capture process ( $r$ -process) nucleosynthesis in the tidal ejecta of a neutron star--neutron star merger and show that it is a key fission channel that shapes the final abundances near the second $r$ -process peak.
nucl-thastro-ph.SRApJ(2018)·92 citations
02
Strangeness $S = - 1$ hyperon-nucleon interactions: chiral effective field theory vs. lattice QCD
Jing Song🇨🇳 · Kai-Wen Li🇨🇳 · Li-Sheng Geng🇨🇳
Hyperon-nucleon interactions serve as basic inputs to studies of hypernuclear physics and dense (neutron) stars. Unfortunately, a precise understanding of these important quantities have lagged far behind that of the nucleon-nucleon interaction due to lack of high precision experimental data. Historically, hyperon-nucleon interactions are either formulated in quark models or meson exchange models. In recent years, lattice QCD simulations and chiral effective field theory approaches start to offer new insights from first principles. In the present work, we contrast the state of art lattice QCD simulations with the latest chiral hyperon-nucleon forces and show that the leading order relativistic chiral results can already describe the lattice QCD data reasonably well. Given the fact that the lattice QCD simulations are performed with pion masses ranging from the (almost) physical point to 700 MeV, such studies provide a highly non-trivial check on both the chiral effective field theory approaches as well as lattice QCD simulations. Nevertheless more precise lattice QCD simulations are eagerly needed to refine our understanding of hyperon-nucleon interactions.
nucl-thhep-lathep-phPRC(2018)·41 citations
03
Pseudorapidity distribution and decorrelation of anisotropic flow within CLVisc hydrodynamics
Long-Gang Pang🇨🇳 · Hannah Petersen🇩🇪 · Xin-Nian Wang🇨🇳
Studies of fluctuations and correlations of soft hadrons and hard and electromagnetic probes of the dense and strongly interacting medium require event-by-event hydrodynamic simulations of high-energy heavy-ion collisions that are computing intensive. We develop a (3+1)D viscous hydrodynamic model -- CLVisc that is parallelized on Graphics Processing Unit (GPU) using Open Computing Language (OpenCL) with 60 times performance increase for space-time evolution and more than 120 times for the Cooper-Frye particlization relative to that without GPU parallelization. The pseudo-rapidity dependence of anisotropic flow $v_{n} (η)$ are then computed in CLVisc with initial conditions given by the A Multi-Phase Transport (AMPT) model, with energy density fluctuations both in the transverse plane and along the longitudinal direction. Although the magnitude of $v_{n} (η)$ and the ratios between $v_{2} (η)$ and $v_{3} (η)$ are sensitive to the effective shear viscosity over entropy density ratio $η_{v} / s$ , the shape of the $v_{n} (η)$ distributions in $η$ do not depend on the value of $η_{v} / s$ . The decorrelation of $v_{n}$ along the pseudo-rapidity direction due to the twist and fluctuation of the event-planes in the initial parton density distributions is also studied. The decorrelation observable $r_{n} (η^{a}, η^{b})$ between $v_{n} {- η^{a}}$ and $v_{n} {η^{a}}$ with the auxiliary reference window $η^{b}$ is found not sensitive to $η_{v} / s$ when there is no initial fluid velocity. For small $η_{v} / s$ , the initial fluid velocity from mini-jet partons introduces sizable splitting of $r_{n} (η^{a}, η^{b})$ between the two reference rapidity windows $η^{b} \in [3, 4]$ and $η^{b} \in [4.4, 5.0]$ , as has been observed in experiment. The implementation of CLVisc and guidelines on how to efficiently parallelize scientific programs on GPUs are also provided.
nucl-thhep-phphysics.comp-phphysics.flu-dynPRC(2018)·213 citations

Affiliations

first authorsco-authorsvia INSPIRE

β-delayed fission in r-process nucleosynthesis

Strangeness S=−1 hyperon-nucleon interactions: chiral effective field theory vs. lattice QCD

Pseudorapidity distribution and decorrelation of anisotropic flow within CLVisc hydrodynamics

Affiliations

$β$ -delayed fission in $r$ -process nucleosynthesis

Strangeness $S = - 1$ hyperon-nucleon interactions: chiral effective field theory vs. lattice QCD