Nuclear Theory·nucl-th

Thursday·May 9, 2019

9 papers—8 primary·1 cross-listed

01
Yields of weakly-bound light nuclei as a probe of the statistical hadronization model
Yiming Cai🇺🇸 · Thomas D. Cohen🇺🇸 · Boris A. Gelman🇺🇸 · Yukari Yamauchi🇺🇸
The statistical hadronization model is a simple and efficient phenomenological framework in which the relative yields for very high energy heavy ion collisions are essentially determined by a single model parameter---the chemical freeze-out temperature. Recent measurements of yields of hadrons and light nuclei covering over 9 orders of magnitudes from the ALICE collaboration at the LHC were described by the model with remarkable accuracy with a chemical freeze-out temperature of 156.5 $\pm$ 1.5 MeV. A key physical question is whether the freeze-out temperature can be understood, literally, as the temperature at which the various species of an equilibrated gas of hadrons (including resonances) and nuclei chemically freeze out as the model assumes, or whether it successfully parametrizes the yield data for a different reason. The yields of weakly-bound light nuclei---the deuteron and the hypertriton---provide insights into this issue. The analysis indicates that a key assumption underlying the model---that hadrons (and nuclei), just prior to chemical freeze-out temperature, are in thermal equilibrium and are sufficiently dilute as to have particle distributions accurately described statistically by a nearly ideal gas of hadrons and nuclei with masses given by their free space values---appears to be inconsistent with the chemical freeze-out temperature output by the model, at least for these weakly-bound nuclei.
nucl-thhep-exhep-phnucl-exPRC(2019)·27 citations
02
Ab Initio Simulations of Light Nuclear Systems Using Eigenvector Continuation and Auxiliary Field Monte Carlo
Dillon K. Frame🇺🇸
In this work, we discuss a new method for calculation of extremal eigenvectors and eigenvalues in systems or regions of parameter space where direct calculation is problematic. This technique relies on the analytic continuation of the power series expansion for the eigenvector around a point in the complex plane. We start this document by introducing the background material relevant to understand the basics of quantum mechanics and quantum field theories on the lattice, how we perform our numerical simulations, and how this relates to the nuclear physics we probe. We then move to the mathematical formalism of the eigenvector continuation, which is rooted in analytic function theory and linear algebra. We then discuss how these techniques are implemented numerically, with a discussion about the computational costs. Finally, we discuss applications of this method to full, quantum many-body systems. These include neutron matter, the Bose-Hubbard model, the Lipkin model, and the Coulomb interaction in light nuclei with LO chiral forces. These systems cover two categories of interest to the field: systems with a substantial sign problem, or systems that exhibit quantum phase transitions.
nucl-thhep-lat8 citations
03
Restoration of pseudo-spin symmetry in $N = 32$ and $34$ isotones described by relativistic Hartree-Fock theory
Zheng Zheng Li · Shi Yao Chang · Qiang Zhao · Wen Hui Long · Yi Fei Niu
Restoration of pseudo-spin symmetry (PSS) along the $N = 32$ and $34$ isotonic chains and the physics behind are studied by applying the relativistic Hartree-Fock theory with effective Lagrangian PKA1. Taking the proton pseudo-spin partners $(π 2 s_{1/2}, π 1 d_{3/2})$ as candidates, systematic restoration of PSS along both isotonic chains is found from sulphur (S) to nickel (Ni), while distinct violation from silicon (Si) to sulphur is discovered near the drip lines. The effects of the tensor-force components introduced naturally by the Fock terms are investigated, which can only partly interpret the systematics from calcium to nickel, but fail for the overall trends. Further analysis following the Schrödinger-like equation of the lower component of Dirac spinor shows that the contributions from the Hartree terms dominate the overall systematics of the PSS restoration, and such effects can be self-consistently interpreted by the evolution of the proton central density profiles along both isotonic chains. Specifically the distinct PSS violation is found to tightly relate with the dramatic changes from the bubble-like density profiles in silicon to the central-bumped ones in sulphur.
nucl-thCPC(2019)·7 citations
04
Neutron capture cross sections from surrogate reaction data and theory: connecting the pieces with a Markov-Chain Monte Carlo approach
Oliver Gorton · Jutta E. Escher
The neutron capture cross section for $^{90} Z r (n, γ)$ has recently been determined using surrogate $^{92} Z r (p, d γ)$ data and nuclear reaction theory. That work employed an approximate fitting method based on Bayesian Monte Carlo sampling to determine parameters needed for calculating the $^{90} Z r (n, γ)$ cross section. Here, we improve the approach by introducing a more sophisticated Markov Chain Monte Carlo sampling method. We present preliminary results.
nucl-thSpringer Proc.Phys.(2020)·0 citations
05
Calculated Inter-band B(E2)'s in the p-f Shell
Levering Wolfe · Larry Zamick
Whereas previous works for B(E2)'s in the even-even Ti isotopes focused on yrast transitions we here also consider inter-band transitions to a second group i.e. states like 1_{1} , 2_{2}, 3_{1} , 4_{2} , 5_{1}e.t.c.. We focus on variations from one even-even Ti isotope to the next. We make a qualitative comparison with similar transitions in a heavier deformed nucleus.
nucl-thnucl-exNPA(2019)·1 citation
06
Mutual derivation between arbitrary distribution forms of momenta and momentum components
Pei-Pin Yang🇨🇳 · Qi Wang🇨🇳 · Fu-Hu Liu🇨🇳
The mutual derivation between arbitrary distribution forms of momenta and momentum components of particles produced in an isotropic emission source are systematically studied in terms of probability theory and mathematical statistics. The distributions of rapidities and pseudorapidities are expediently studied. As an example, the classical and relativistic ideal gas models are used to show these distributions by the analytic and Monte Carlo methods. As an application, the experimental rapidity and transverse momentum spectra of light flavor particles produced in high energy collisions are analyzed by a multi-component relativistic ideal gas model in which the single model can be replaced by other models and distributions.
nucl-thhep-exnucl-exphysics.class-ph+1Int.J.Theor.Phys.(2019)·8 citations
07
Feed-down effect on $Λ$ spin polarization
Xiao-Liang Xia🇨🇳 · Hui Li🇨🇳 · Xu-Guang Huang🇨🇳 · Huan Zhong Huang🇨🇳
We develop a theoretical framework to study the feed-down effect of higher-lying strange baryons on the spin polarization of the $Λ$ hyperon. In this framework, we consider two-body decays through strong, electromagnetic, and weak processes and derive general formulas for the angular distribution and spin polarization of the daughter particle by adopting the helicity formalism. Using the realistic experimental data as input, we explore the feed-down contribution to the global and the local $Λ$ polarizations and find that such a contribution suppresses the primordial $Λ$ polarization, which is not strong enough to resolve the discrepancy between the current theoretical and the experimental results on the azimuthal-angle dependence of $Λ$ polarization. Our paper may also be useful for the measurement of spin polarization of baryons heavier than $Λ$ (e.g., $Ξ^{-}$ ) in future experiments.
nucl-thhep-phPRC(2019)·91 citations
08
Polarization transfer in hyperon decays and its effect in relativistic nuclear collisions
F. Becattini (University of Florence)🇮🇹 · Gaoqing Cao (Sun Yat-Sen University)🇨🇳 · Enrico Speranza (University of Frankfurt)🇩🇪
We calculate the contribution to the polarization of $Λ$ hyperons in relativistic nuclear collisions at high energy from the decays of $Σ^{*} (1385)$ and $Σ^{0}$ , which are the predominant sources of $Λ$ production besides the primary component, as a function of the $Λ$ momentum. Particularly, we estimate the longitudinal component of the mean spin vector as a function of the azimuthal angle in the transverse plane, assuming that primary $Σ^{*}$ and $Σ^{0}$ polarization follow the predictions of local thermodynamic equilibrium in a relativistic fluid. Provided that the rapidity dependence around midrapidity of polarization is negligible, we find that this component of the overall spin vector has a very similar pattern to the primary one. Therefore, we conclude that the secondary decays cannot account for the discrepancy in sign between experimental data and hydrodynamic model predictions of the longitudinal polarization of $Λ$ hyperons recently measured by the STAR experiment at RHIC.
nucl-thhep-phEPJC(2019)·103 citations
09
Partonic angular momentum in the nucleon's chiral periphery
Carlos Granados🇺🇸 · Christian Weiss🇺🇸
We study the nucleon's partonic angular momentum (AM) content at peripheral transverse distances $b = O (M_{π}^{- 1})$ , where the structure is governed by chiral dynamics. We compute the nucleon form factors of the energy-momentum tensor in chiral effective field theory (ChEFT) and construct the transverse densities of AM at fixed light-front time. In the periphery the spin density is suppressed, and the AM is predominantly orbital. In the first-quantized representation of ChEFT in light-front form, the field-theoretical AM density coincides with the quantum-mechanical orbital AM density of the soft pions in the nucleon's periphery.
↳ hep-phnucl-thPLB(2019)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE