Nuclear Theory·nucl-th

Tuesday·December 22, 2015

23 papers—17 primary·6 cross-listed

01
Screening of Nucleon Electric Dipole Moments in Nuclei
Satoru Inoue🇺🇸 · Vladimir Gudkov🇺🇸 · Matthias R. Schindler🇺🇸 · Young-Ho Song🇰🇷
A partial screening of nucleon electric dipole moments (EDMs) in nuclear systems, which is related to the Schiff mechanism known for neutral atomic systems, is discussed. It is shown that the direct contribution from the neutron EDM to the deuteron EDM is partially screened by about 1% in a zero-range approximation calculation.
nucl-thhep-phPRC(2016)·6 citations
02
Shell-model calculation of neutrinoless double- $β$ decay of $^{76}$ Ge
R.A.Sen'kov🇺🇸 · M.Horoi🇺🇸
In this article we present a more detailed version of our recent Rapid Communication [Phys. Rev. C 90, 051301(R) (2014)] where we calculate the nuclear matrix elements for neutrinoless double- $β$ decay of $^{76}$ Ge. For the calculations we use a novel method that has perfect convergence properties and allows one to obtain the nonclosure nuclear matrix elements for $^{76}$ Ge with a 1% accuracy. We present a new way of calculation of the optimal closure energy, using this energy with the closure approximation provides the most accurate closure nuclear matrix elements. In addition, we present a new analysis of the heavy-neutrino-exchange nuclear matrix elements, and we compare occupation probabilities and Gamow-Teller strength with experimental data.
nucl-thPRC(2016)·59 citations
03
Correlated fluctuations near the QCD critical point
Lijia Jiang🇨🇳 · Pengfei Li🇨🇳 · Huichao Song (Peking U.)🇨🇳
In this paper, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy dependent cumulant $C_{4}$ and $κ σ^{2}$ of net protons through tuning the related parameters. However, the calculated $C_{2}$ and $C_{3}$ with both Poisson and Binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. In order to qualitatively and quantitatively describe the experimental data, the dynamical critical fluctuations and more realistic non-critical fluctuation baselines should be investigated in the near future.
nucl-thhep-phnucl-exPRC(2016)·69 citations
04
A Complete Equation of State for Astrophysical Simulations
Hong Shen
We construct a complete equation of state (EOS) covering a wide range of temperature, proton fraction, and baryon density for the use of astrophysical simulations. We employ the relativistic mean-field (RMF) theory to describe nuclear interactions and adopt the Thomas-Fermi approximation to describe the nonuniform nuclear matter. The uniform matter and nonuniform matter are studied consistently using the same RMF theory.
nucl-thActa Astron.Sin.Suppl.(2015)·0 citations
05
The effect of momentum deposition during fireball evolution on flow anisotropy
Martin Schulc🇨🇿 · Boris Tomasik🇨🇿
The highest LHC energies give rise to production of many pairs of hard partons which deposit four-momentum into the expanding fireball matter. We argue that it is necessary to include momentum deposition during fireball evolution into 3+1 dimensional hydrodynamic simulations of the collision. This influence cannot be accounted for simply by modifying initial conditions of the simulation. The resulting contribution to flow anisotropy is correlated with the fireball geometry and causes an increase of the elliptic flow in non-central collisions. The results are presented for various scenarios with energy and momentum deposition to clearly demonstrate this effect.
nucl-thJ.Phys.G(2016)·2 citations
06
Does non-monotonic behavior of directed flow signal the onset of deconfinement?
Yasushi Nara🇯🇵 · Akira Ohnishi🇯🇵
We investigate the effects of nuclear mean-field as well as the formation and decay of nuclear clusters on the directed flow $v_{1}$ in high energy nucleus-nucleus collisions from $s_{N N} = 7.7$ GeV to 27 GeV incident energies within a transport model. Specifically, we use the JAM transport model in which potentials are implemented based on the framework of the relativistic quantum molecular dynamics. Our approach reproduces the rapidity dependence of directed flow data up to $s_{N N} \approx 8$ GeV showing the significant importance of mean-field. However, the slopes of $d v_{1} / d y$ at mid-rapidity are calculated to be positive at $s_{N N} = 11.7$ and 19.6 GeV, and becomes negative above 27 GeV. Thus the result from the JAM hadronic transport model with nuclear mean-field approach is incompatible with the data. Therefore within our approach, we conclude that the excitation function of the directed flow cannot be explained by the hadronic degree of freedom alone.
nucl-thhep-phnucl-exNPA(2016)·11 citations
07
Extracting shear viscosity of the Quark Gluon Plasma in the presence of bulk viscosity
Jacquelyn Noronha-Hostler🇺🇸
One of the most remarkable features of the Quark Gluon Plasma is its nearly perfect fluidity behavior indicated by the small shear viscosity to entropy density ratio obtained from fitting relativistic viscous hydrodynamics flow harmonics to experimental data. In recent years, bulk viscosity has also been considered in the context of event-by-event relativistic hydrodynamics and it has been found to have a non-trivial interplay with shear viscosity. In this paper some of the issues are discussed that require further work when extracting the shear viscosity to entropy density ratio in the presence of a non-zero bulk viscosity.
nucl-thhep-ph11 citations
08
Comparative study of fusion barriers using Skyrme interactions and the energy density functional
O.N.Ghodsi · F.Torabi
Using different Skyrme interactions, we have carried out a comparative analysis of fusion barriers for a wide range of interacting nuclei in the framework of semiclassical Skyrme energy density formalism. The results of our calculations reveal that SVI, SII, and SIII Skyrme forces are able to reproduce the empirical values of barrier heights with higher accuracy than the other considered forces in this formalism. It is also shown that the calculated nucleus-nucleus potentials derived from such Skyrme interactions are able to explain the fusion cross sections at energies near and above the barrier.
nucl-thPRC(2015)·10 citations
09
Elliptic Anisotropy $v_{2}$ May Be Dominated by Particle Escape instead of Hydrodynamic Flow
Zi-Wei Lin🇺🇸 · Liang He🇺🇸 · Terrence Edmonds🇺🇸 · Feng Liu🇨🇳 · Denes Molnar🇺🇸 · Fuqiang Wang🇺🇸
It is commonly believed that azimuthal anisotropies in relativistic heavy ion collisions are generated by hydrodynamic evolution of the strongly interacting quark-gluon plasma. Here we use transport models to study how azimuthal anisotropies depend on the number of collisions that each parton suffers. We find that the majority of $v_{2}$ comes from the anisotropic escape of partons, not from the parton collective flow, for semi-central Au+Au collisions at 200A GeV. As expected, the fraction of $v_{2}$ from the anisotropic particle escape is even higher for smaller systems such as d+Au. Our transport model results also confirm that azimuthal anisotropies would be dominated by hydrodynamic flow at unrealistically-high parton cross sections. Our finding thus naturally explains the similarity of azimuthal anisotropies in small and large systems; however, it presents a challenge to the paradigm of anisotropic flow.
nucl-thnucl-exNPA(2016)·43 citations
10
An estimate of the bulk viscosity of the hadronic medium
Golam Sarwar🇮🇳 · Sandeep Chatterjee🇮🇳 · Jan-e Alam🇮🇳
The bulk viscosity ( $ζ$ ) of the hadronic medium has been estimated within the ambit of the Hadron Resonance Gas (HRG) model including the Hagedorn density of states. The HRG thermodynamics within a grand canonical ensemble provides the mean hadron number as well as its fluctuation. The fluctuation in the chemical composition of the hadronic medium in the grand canonical ensemble can result in non-zero divergence of the hadronic fluid flow velocity, allowing us to estimate the $ζ$ of the hadronic matter upto a relaxation time. We study the influence of the hadronic spectrum on $ζ$ and find its correlation with the conformal symmetry breaking (CSB) measure, $ϵ - 3 P$ . We estimate $ζ$ along the contours with constant, $S / N_{B}$ (total entropy/net baryon number) in the $T - μ$ plane (temperature-baryonic chemical potential) for $S / N_{B} = 30, 45$ and 300. We also assess the value of $ζ$ on the chemical freezeout curve for various centre of mass energy ( $s_{N N}$ ) and find that the bulk viscosity to entropy density ratio, $ζ / s$ is larger at FAIR than LHC energies.
nucl-thhep-phJ.Phys.G(2017)·17 citations
11
Residue cross sections of $^{50}$ Ti-induced fusion reactions based on the two-step model
Ling Liu🇨🇳 · Caiwan Shen🇨🇳 · Qingfeng Li🇨🇳 · Ya Tu🇨🇳 · Xiaobao Wang🇨🇳 · Yongjia Wang🇨🇳
$^{50}$ Ti-induced fusion reactions to synthesize superheavy elements are studied systematically with the two-step model developed recently, where fusion process is divided into approaching phase and formation phase. Furthermore, the residue cross sections for different neutron evaporation channels are evaluated with the statistical evaporation model. In general, the calculated cross sections are much smaller than that of $^{48}$ Ca-induced fusion reactions, but the results are within the detection capability of experimental facilities nowadays. The maximum calculated residue cross section for producing superheavy element $Z = 119$ is in the reaction $^{50}$ Ti+ $^{247}$ Bk in $3 n$ channels with $σ_{res} (3 n) = 0.043$ pb at $E^{*}$ = 37.0 MeV.
nucl-thEPJA(2016)·26 citations
12
Photon and dilepton production at the Facility for Antiproton and Ion Research and the beam energy scan program at the Relativistic Heavy-Ion Collider using coarse-grained microscopic transport simulations
Stephan Endres🇩🇪 · Hendrik van Hees🇩🇪 · Marcus Bleicher🇩🇪
We present calculations of dilepton and photon spectra for the energy range $E_{lab} = 2 - 35$ $A$ GeV which will be available for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-Proton and Ion Research (FAIR). The same energy regime will also be covered by phase II of the Beam Energy Scan at the Relativistic Heavy-Ion Collider (RHIC-BES). Coarse-grained dynamics from microscopic transport calculations of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to determine temperature and chemical potentials, which allows for the use of dilepton and photon-emission rates from equilibrium quantum-field theory calculations. The results indicate that non-equilibrium effects, the presence of baryonic matter and the creation of a deconfined phase might show up in specific manners in the measurable dilepton invariant mass spectra and in the photon transverse momentum spectra. However, as the many influences are difficult to disentangle, we argue that the challenge for future measurements of electromagnetic probes will be to provide a high precision with uncertainties much lower than in previous experiments. Furthermore, a systematic study of the whole energy range covered by CBM at FAIR and RHIC-BES is necessary to discriminate between different effects, which influence the spectra, and to identify possible signatures of a phase transition.
nucl-thhep-phPRC(2016)·35 citations
13
Extending the truncated Dyson-Schwinger equation to finite temperatures
S. M. Dorkin🇷🇺 · M. Viebach🇩🇪 · L. P. Kaptari🇷🇺 · B. Kampfer🇩🇪
In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value $T_{c}$ the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than $T_{c}$ . For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.
nucl-thhep-phJ.Mod.Phys.(2016)·6 citations
14
In search of chiral magnetic effect: separating flow-driven background effects and quantifying anomaly-induced charge separations
Xu-Guang Huang🇨🇳 · Yi Yin🇺🇸 · Jinfeng Liao🇺🇸
We report our recent progress on the search of Chiral Magnetic Effect (CME) by developing new measurements as well as by hydrodynamic simulations of CME and background effects, with both approaches addressing the pressing issue of separating flow-driven background contributions and possible CME signal in current heavy ion collision measurements.
nucl-thhep-phNPA(2016)·17 citations
15
A further update on possible crises in nuclear-matter theory
W. H. Dickhoff
The ancient problem of the saturation of symmetric nuclear matter is reviewed with an update on the status of the crises that were identified at an early stage by John Clark. We discuss how the initial problem with variational calculations providing more binding than the two hole-line contribution for the same interaction was overcome by calculations including three hole-line contributions without however reproducing the empirical nuclear saturation properties. It is argued that this remaining problem is still open because many solutions have been proposed or ad hoc adjustments implemented without generating universal agreement on the proper interpretation of the physics. The problem of nuclear saturation therefore persists leading to the necessity of an analysis of the way the nuclear saturation properties are obtained from experimental data. We clarify the role of short-range correlations and review results for nuclear saturation when such ingredients are completely taken into account using the Green's function method. The role of long-range correlations is then analyzed with special emphasis on the importance of attractive pion-dominated excitation modes which inevitably lead to higher saturation densities than observed. Because such modes have no counterpart in finite nuclear systems, it is therefore argued that they should not be considered when calculating nuclear matter properties. The remaining open question is then whether long-range correlations in finite nuclei which in turn have no counterpart in infinite matter, represent the remaining missing ingredient in this analysis.
nucl-thJ.Phys.Conf.Ser.(2016)·2 citations
16
Forging the Link between Nuclear Reactions and Nuclear Structure
W. H. Dickhoff
A review of the recent applications of the dispersive optical model (DOM) is presented. Emphasis is on the nonlocal implementation of the DOM that is capable of describing ground-state properties accurately when data like the nuclear charge density are available. The DOM, conceived by Claude Mahaux, provides a unified description of both elastic nucleon scattering and structure information related to single-particle properties below the Fermi energy. We have recently introduced a nonlocal dispersive optical potential for both the real and imaginary part. Nonlocal absorptive potentials yield equivalent elastic differential cross sections for $^{40}$ Ca as compared to local ones but change the $ℓ$ -dependent absorption profile suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by $(e, e^{'} p)$ and $(p, 2 p)$ reactions are correctly described, including the energy distribution of about 10\% high-momentum protons obtained at Jefferson Lab. The nonlocal DOM allows a complete description of experimental data both above (up to 200 MeV) and below the Fermi energy in $^{40}$ Ca. It is further demonstrated that elastic nucleon-nucleus scattering data constrain the spectral strength in the continuum of orbits that are nominally bound in the independent-particle model. Extension of this analysis to $^{48}$ Ca allows a prediction of the neutron skin of this nucleus that is larger than most predictions made so far.
nucl-thEPJ Web Conf.(2016)·2 citations
17
The EOS of neutron matter and the effect of $Λ$ hyperons to neutron star structure
Stefano Gandolfi🇺🇸 · Diego Lonardoni🇺🇸
The structure of neutron stars is determined by the equation of state of the matter inside the star, which relies on the knowledge of nuclear interactions. While radii of neutron stars mostly depend on the equation of state of neutron matter at nuclear densities, their maximum mass can be drastically affected by the appearance of hyperons at higher densities in the inner core of the star. We summarize recent quantum Monte Carlo results on the calculation of the equation of state of neutron matter at nuclear and higher densities. We report about the development of realistic hyperon-nucleon interactions based on the available experimental data for light- and medium-heavy hypernuclei and on the effect of $Λ$ hyperons to the neutron star structure.
nucl-thJPS Conf.Proc.(2017)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE