Nuclear Theory·nucl-th

Tuesday·January 12, 2016

14 papers—9 primary·5 cross-listed

01
Neutron Skins and Halo Orbits in the $s d$ and $p f$ shells
J. Bonnard🇮🇹 · S. M. Lenzi🇮🇹 · A. P. Zuker🇮🇹
The strong dependence of Coulomb energies on nuclear radii makes it possible to extract the latter from calculations of the former. The resulting estimates of neutron skins indicate that two mechanisms are involved. The first one---isovector monopole polarizability---amounts to noting that when a particle is added to a system it drives the radii of neutrons and protons in different directions, tending to equalize the radii of both fluids independently of the neutron excess. This mechanism is well understood and the Duflo-Zuker (small) neutron skin values derived 14 years ago are consistent with recent measures and estimates. The alternative mechanism involves halo orbits whose huge sizes tend to make the neutron skins larger and have a subtle influence on the radial behavior of $s d$ and $p f$ shell nuclei. In particular, they account for the sudden rise in the isotope shifts of nuclei beyond $N = 28$ and the near constancy of radii in the $A = 40 - 56$ region. This mechanism, detected here for the first time, is not well understood and may well go beyond Efimov physics usually associated to halo orbits.
nucl-thPRL(2016)·32 citations
02
Hydrodynamic fluctuations and dissipation in an integrated dynamical model
Koichi Murase🇯🇵 · Tetsufumi Hirano🇯🇵
We develop a new integrated dynamical model to investigate the effects of the hydrodynamic fluctuations on observables in high-energy nuclear collisions. We implement hydrodynamic fluctuations in a fully 3-D dynamical model consisting of the hydrodynamic initialization models of the Monte-Carlo Kharzeev-Levin-Nardi model, causal dissipative hydrodynamics and the subsequent hadronic cascades. By analyzing the hadron distributions obtained by massive event-by-event simulations with both of hydrodynamic fluctuations and initial-state fluctuations, we discuss the effects of hydrodynamic fluctuations on the flow harmonics, $v_{n}$ and their fluctuations.
nucl-thhep-phnucl-exNPA(2016)·52 citations
03
Establishing mass spectrum of $S = - 1$ hyperon resonances via a dynamical coupled-channels analysis of $K^{-} p$ reactions
Hiroyuki Kamano🇯🇵
We report our recent effort for the extraction of resonance parameters (complex pole mass and residues etc.) associated with Lambda* and Sigma* hyperons. This was accomplished via a comprehensive partial-wave analysis of the data for K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi reactions from the thresholds up to W=2.1 GeV within a dynamical coupled-channels approach. The results suggest a possible existence of new narrow J^P=3/2^+ \Lambda resonance with pole mass 1671^{+2}_{-8} -i(5^{+11}_{-2}) MeV, located close to the eta Lambda threshold. This resonance is found to be responsible for reproducing the data for K^-p --> eta Lambda differential cross sections near the threshold, and thus the data seem favor its existence. The extracted poles for J^P=1/2^- Lambda resonances below the barK N threshold, including Lambda(1405), are also presented.
nucl-thhep-phnucl-exJPS Conf.Proc.(2017)·0 citations
04
Fixed points of the SRG evolution and the on-shell limit of the nuclear force
E. Ruiz Arriola🇪🇸 · S. Szpigel🇧🇷 · V. S. Timoteo🇧🇷
We study the infrared limit of the similarity renormalization group (SRG) using a simple toy model for the nuclear force aiming to investigate the fixed points of the SRG evolution with both the Wilson and the Wegner generators. We show how a fully diagonal interaction at the similarity cutoff $λ \to 0$ may be obtained from the eigenvalues of the hamiltonian and quantify the diagonalness by means of operator norms. While the fixed points for both generators are equivalent when no bound-states are allowed by the interaction, the differences arising from the presence of the Deuteron bound-state can be disentangled very clearly by analyzing the evolved interactions in the infrared limit $λ \to 0$ on a finite momentum grid. Another issue we investigate is the location on the diagonal of the hamiltonian in momentum-space where the SRG evolution places the Deuteron bound-state eigenvalue once it reaches the fixed point. This finite momentum grid setup provides an alternative derivation of the celebrated trace identities, as a by product. The different effects due to either the Wilson or the Wegner generators on the binding energies of $A = 2, 3, 4$ systems are investigated and related to the ocurrence of a Tjon-line which emerges as the minimum of an avoided crossing between $E_{α} = 4 E_{t} - 3 E_{d}$ and $E_{α} = 2 E_{t}$ . All infrared features of the flow equations are illustrated using the toy model for the two-nucleon $S$ -waves.
nucl-thhep-phAnnals Phys.(2016)·15 citations
05
Hartree-Fock and Random Phase Approximation theories in a many-fermion solvable model
Giampaolo Co' · Stefano De Leo
We present an ideal system of interacting fermions where the solutions of the many-body Schroedinger equation can be obtained without making approximations. These exact solutions are used to test the validity of two many-body effective approaches, the Hartree-Fock and the Random Phase Approximation theories. The description of the ground state done by the effective theories improves with increasing number of particles.
nucl-thMod.Phys.Lett.A(2015)·10 citations
06
Nonclassical Particle Transport in the 1-D Diffusive Limit
Richard Vasques · Rachel Slaybaugh · Kai Krycki
This paper provides numerical results that demonstrate the validity of the nonclassical diffusion approximation to the nonclassical transport equation in certain 1-D diffusive systems. This result provides a more solid foundation in which to improve this theory for relevant nuclear applications.
nucl-thTrans.Amer.Nucl.Soc.(2016)·3 citations
07
Energetic Light Fragment Production Capability in MCNP6
Leslie M. Kerby · Stepan G. Mashnik · Konstantin K. Gudima · Arnold J. Sierk · Jeffrey S. Bull · Michael R. James
The goal of this research is to enable MCNP6 to produce high-energy light fragments. These energetic light fragments may be emitted by our models through three processes: Fermi breakup, preequilibrium, and coalescence. We explore the emission of light fragments through each of these mechanisms and demonstrate an improved agreement with experimental data achieved by extending precompound models to include emission of fragments heavier than $^{4}$ He.
nucl-th0 citations
08
Electromagnetic Radiation from QCD Matter: Theory Overview
Chun Shen (McGill U.)🇨🇦
Recent theory developments in electromagnetic radiation from relativistic heavy-ion collisions are reviewed. Electromagnetic observables can serve as a thermometer, a viscometer, and tomographic probes to the collision system. The current status of the "direct photon flow puzzle" is highlighted.
nucl-thhep-phnucl-exNPA(2016)·42 citations
09
Jets in d(p)-A Collisions: Color Transparency or Energy Conservation
Michael Kordell II🇺🇸 · Abhijit Majumder🇺🇸
The production of jets, and high momentum hadrons from jets, produced in deuteron ( $d$ )- $A u$ collisions at the relativistic heavy-ion collider (RHIC) and proton ( $p$ )- $P b$ collisions at the large hadron collider (LHC) are studied as a function of centrality, a measure of the impact parameter of the collision. A modified version of the event generator PYTHIA, widely used to simulate $p$ - $p$ collisions, is used in conjunction with a nuclear Monte-Carlo event generator which simulates the locations of the nucleons within a large nucleus. We demonstrate how events with a hard jet may be simulated, in such a way that the parton distribution function of the projectile is frozen during its interaction with the extended nucleus. Using our approach, we demonstrate that the puzzling enhancement seen in peripheral events at RHIC and the LHC, as well as the suppression seen in central events at the LHC are mainly due to mis-binning of central and semi-central events, containing a jet, as peripheral events. This occurs due to the suppression of soft particle production away from the jet, caused by the depletion of energy available in a nucleon of the deuteron (in $d$ - $A u$ at RHIC) or in the proton (in $p$ - $P b$ at LHC), after the production of a hard jet. We conclude that partonic correlations built out of simple energy conservation are mostly responsible for such an effect.
nucl-thhep-phnucl-exPRC(2018)·37 citations
10
Cigar-shaped quarkonia under strong magnetic field
Kei Suzuki🇯🇵 · Tetsuya Yoshida🇯🇵
Heavy quarkonia in a homogeneous magnetic field are analyzed by using a potential model with constituent quarks. To obtain anisotropic wave functions and corresponding eigenvalues, the cylindrical Gaussian expansion method is applied, where the anisotropic wave functions are expanded by a Gaussian basis in the cylindrical coordinates. Deformation of the wave functions and the mass shifts of the $S$ -wave heavy quarkonia ( $η_{c}$ , $J / ψ$ , $η_{c} (2 S)$ , $ψ (2 S)$ and bottomonia) are examined for the wide range of external magnetic field. The spatial structure of the wave functions changes drastically as adjacent energy levels cross each other. Possible observables in heavy-ion collision experiments and future lattice QCD simulations are also discussed.
↳ hep-phhep-latnucl-exnucl-thPRD(2016)·32 citations
11
Classic Calculations of Static Properties of the Nucleons reexamined
N. F. Nasrallah🇱🇧
Classic calculations of the magnetic moments mu_p and mu_n of the nucleons using the traditional exponential kernel show instability with respect to variations of the Borel mass as well as arbitrariness with respect to the choice of the onset of perturbative QCD. The use of a polynomial kernel, the coefficients of which are determined by the masses of the nucleon resonances stabilizes the calculation and provides much better damping of the unknown contribution of the nucleon continuum. The method is also applied to the evaluation of the coupling gA of proton to the axial current and to the strong part of the neutron-proton mass difference Delta M_np. All these quantities depend sensitively on the value of the 4-quark condensate < 0 | qqqq | 0 > and the value < 0 | qqqq | 0 > ~ 1.5< 0 | qq | 0 >^2 reproduces the experimental results.
↳ hep-phnucl-thPRC(2016)·0 citations
12
Drag and Diffusion of Heavy Quarks in a hot and anisotropic QCD medium
P. K. Srivastava🇮🇳 · Binoy Krishna Patra🇮🇳
The propagation of heavy quarks (HQs) in a medium was quite often modeled by the Fokker-Plank (FP) equation. Since the transport coefficients, related to drag and diffusion processes are the main ingredients in the FP equation, the evolution of HQs is thus effectively controlled by them. At the initial stage of the relativistic heavy ion collisions, asymptotic weak-coupling causes the free-streaming motions of partons in the beam direction and the expansion in transverse directions are almost frozen, hence an anisotropy in the momentum space sets in. Since HQs are too produced in the same time therefore the study of the effect of momentum anisotropy on the drag and diffusion coefficients becomes advertently desirable. In this article we have thus studied the drag and diffusion of HQs in the anisotropic medium and found that the presence of the anisotropy reduces both drag and diffusion coefficients. In addition, the anisotropy introduces an angular dependence to both the drag and diffusion coefficients, as a result both coefficients get inflated when the partons are moving transverse to the direction of anisotropy than parallel to the direction of anisotropy.
↳ hep-phnucl-thEPJA(2017)·15 citations
13
Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States
M. Beitel🇩🇪 · C. Greiner🇩🇪 · H. Stoecker🇩🇪
Hagedorn states are the key to understand how all hadrons observed in high energy heavy ion collisions seem to reach thermal equilibrium so quickly. An assembly of Hagedorn states is formed in elementary hadronic or heavy ion collisions at hadronization. Microscopic simulations within the transport model UrQMD allow to study the time evolution of such a pure non-equilibrated Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by using dynamics, which unlike strings, fully respect detailed balance. Propagation, repopulation, rescatterings and decays of Hagedorn states provide the yields of all hadrons up to a mass of m=2.5 GeV. Ratios of feed down corrected hadron multiplicities are compared to corresponding experimental data from the ALICE collaboration at LHC. The quick thermalization within t=1-2 fmo̧f the emerging Hadron Resonance Gas exposes Hagedorn states as a tool to understand hadronization.
↳ hep-phnucl-thPRC(2016)·18 citations
14
Nucleon Resonance Structure Studies Via Exclusive KY Electroproduction
Daniel S. Carman (for the CLAS Collaboration)🇺🇸
Studying the structure of excited nucleon states employing the electroproduction of exclusive reactions is an important avenue for exploring the nature of the non-perturbative strong interaction. The electrocouplings of $N^{*}$ states in the mass range below 1.8~GeV have been determined from analyses of CLAS $π N$ , $η N$ , and $π π N$ data. This work has made it clear that consistent results from independent analyses of several exclusive channels with different couplings and non-resonant backgrounds but the same $N^{*}$ electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying $N^{*}$ states preferentially decay through the $π π N$ channel instead of $π N$ . Data from the $K Y$ channels will therefore be critical to provide an independent analysis to compare the extracted electrocouplings for the high-lying $N^{*}$ states against those determined from the $π N$ and $π π N$ channels. A program to study excited $N^{*}$ state structure in both non-strange and strange exclusive electroproduction channels using CLAS12 will measure differential cross sections and polarization observables to be used as input to extract the $γ_{v} N N^{*}$ electrocoupling amplitudes for the most prominent $N^{*}$ states in the range of invariant energy $W$ up 3~GeV in the virtually unexplored domain of momentum transfers $Q^{2}$ up to 12~GeV $^{2}$ .
↳ nucl-exnucl-thFew Body Syst.(2016)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE