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Nuclear Theory·nucl-th

Monday·November 28, 2016

18 papers—7 primary·11 cross-listed

All18Primary7Cross-lists11
  1. 01

    [Submitted on 23 Nov 2016]

    Equation of state dependence of directed flow in a microscopic transport model

    Yasushi Nara🇯🇵 · Harri Niemi🇩🇪 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪

    We study the sensitivities of the directed flow in Au+Au collisions on the equation of state (EoS), employing the transport theoretical model JAM. The EoS is modified by introducing a new collision term in order to control the pressure of a system by appropriately selecting an azimuthal angle in two-body collisions according to a given EoS. It is shown that this approach is an efficient method to modify the EoS in a transport model. The beam energy dependence of the directed flow of protons is examined with two different EoS, a first-order phase transition and crossover. It is found that our approach yields quite similar results as hydrodynamical predictions on the beam energy dependence of the directed flow; Transport theory predicts a minimum in the excitation function of the slope of proton directed flow and does indeed yield negative directed flow, if the EoS with a first-order phase transition is employed. Our result strongly suggests that the highest sensitivity for the critical point can be seen in the beam energy range of GeV.

    Comments:
    7 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1611.08023 [pdf]
    PLB(2017)·56 citations
  2. 02

    [Submitted on 24 Nov 2016]

    Vorticity in the QGP liquid and hyperon polarization at the RHIC BES energies

    Iu. Karpenko🇮🇹 · F. Becattini🇮🇹

    We calculate the polarization of hyperons in Au-Au collisions at RHIC Beam Energy Scan range GeV in a state-of-the-art 3+1 dimensional cascade + viscous hydro model vHLLE+UrQMD. We find that the polarization of in the out-of-plane direction decreases substantially with collision energy. We explore the connection between the polarization signal and thermal vorticity and discuss the feed-down and hadronic rescattering effects on the mean polarization of all produced hyperons.

    Comments:
    proceedings of Strangeness in Quark Matter 2016 conference, 27 June - 1 July 2016, Berkeley
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1611.08136 [pdf]
    J.Phys.Conf.Ser.(2017)·5 citations
  3. 03

    [Submitted on 25 Nov 2016]

    Extracting kinetic freeze-out temperature and radial flow velocity from an improved Tsallis distribution

    Hai-Ling Lao🇨🇳 · Fu-Hu Liu🇨🇳 · Roy A. Lacey🇺🇸

    We analyze the transverse momentum () spectra of identified particles (, , , and ) produced in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions over a (center-of-mass energy per nucleon pair) range from 14.5 GeV [one of the Relativistic Heavy Ion Collider (RHIC) energies] to 2.76 TeV [one of the Large Hadron Collider (LHC) energies]. For the spectra with a narrow range, an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used. For the spectra with a wide range, a superposition of the improved Tsallis distribution and an inverse power-law is used. Both the extracted kinetic freeze-out temperature () and radial flow velocity () increase with the increase of , which indicates a higher excitation and larger expansion of the interesting system at the LHC. Both the values of and in central collisions are slightly larger than those in peripheral collisions, and they are independent of isospin and slightly dependent on mass.

    Comments:
    We have corrected the pseudorapidity ranges of the data quoted in this paper. The PHENIX data should be in the pseudorapidity range , but not the rapidity range ; and the ALICE data should be in for high transverse momentum region and for low transverse momentum region, but not only . These do not affect the results of the publication
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1611.08391 [pdf]
    EPJA(2017)·51 citations
  4. 04

    [Submitted on 25 Nov 2016]

    Leading order relativistic chiral nucleon-nucleon interaction

    Xiu-Lei Ren🇨🇳 · Kai-Wen Li🇨🇳 · Li-Sheng Geng🇨🇳 · Bing-Wei Long🇨🇳 · Peter Ring🇨🇳 · Jie Meng🇨🇳

    Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian. We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the and phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta , the relativistic results are almost the same as their leading order non-relativistic counterparts.

    Comments:
    12 pages, 4 figures; version to appear in Chinese Physics C
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1611.08475 [pdf]
    CPC(2018)·90 citations
  5. 05

    [Submitted on 25 Nov 2016]

    Nuclear fragmentation and charge-exchange reactions induced by pions in the -resonance region

    Zhao-Qing Feng🇨🇳

    Dynamics of the nuclear fragmentations and the charge exchange reactions in pion-nucleus collisions near the (1232) resonance energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. An isospin, momentum and density-dependent pion-nucleon potential is implemented in the model, which influences the pion dynamics, in particular the kinetic energy spectra, but weakly impacts the fragmentation mechanism. The absorption process in pion-nucleon collisions to form the (1232) resonance dominates the heating mechanism of target nucleus. The excitation energy transferred to the target nucleus increases with the pion kinetic energy and is similar for both and induced reactions. The magnitude of fragmentation of target nucleus weakly depends on the pion energy. The isospin ratio in the pion double charge exchange is influenced by the isospin ingredient of target nucleus.

    Comments:
    11 pages, 12 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1611.08495 [pdf]
    PRC(2016)·17 citations
  6. 06

    [Submitted on 25 Nov 2016]

    Ab initio calculation of the potential bubble nucleus Si

    T. Duguet🇫🇷 · V. Somà🇫🇷 · S. Lecluse🇧🇪 · C. Barbieri🇬🇧 · P. Navrátil🇨🇦

    The possibility that an unconventional depletion in the center of the charge density distribution of certain nuclei occurs due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. We report on ab initio self-consistent Green's function calculations of one of such candidates, Si, together with its Z+2 neighbour S. Binding energies, rms radii and density distributions of the two nuclei as well as low-lying spectroscopy of Si, S, Al and P are discussed. The interpretation of one-nucleon removal and addition spectra in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input inter-nucleon interactions. The prediction regarding the (non-)existence of the bubble structure in Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root mean square radius of S are well reproduced, along with Si and S binding energies, only leaves the NNLO Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of Si, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2-3/2 splitting in the spectrum of Si as compared to S.

    Comments:
    19 pages, 21 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1611.08570 [pdf]
    PRC(2017)·74 citations
  7. 07

    [Submitted on 25 Nov 2016]

    Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions

    Boris Tomasik🇸🇰 · Martin Schulc🇨🇿

    Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.

    Comments:
    6 pages, 4 figures, Proceedings from XII Quark Confinement and the Hadron Spectrum, Thessaloniki, Grece, 28.8.2016-4.9.2016
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1611.08577 [pdf]
    EPJ Web Conf.(2017)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE