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Nuclear Theory·nucl-th

Monday·February 18, 2019

4 papers—4 primary·0 cross-listed

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  1. 01

    [Submitted on 14 Feb 2019]

    Magnetic dipole excitation and its sum rule in nuclei with two valence nucleons

    Tomohiro Oishi · Nils Paar

    Background: Magnetic dipole (M1) excitation is the leading mode of nuclear excitation by the magnetic field, which couples unnatural-parity states. Since the M1 excitation occurs mainly for open-shell nuclei, the nuclear pairing effect is expected to play a role. As expected from the form of operator, this mode may provide the information on the spin-related properties, including the spin component of dineutron and diproton correlations. In general, the sum rule for M1 transition strength has not been derived yet. Purpose: To investigate the M1 excitation of the systems with two valence nucleons above the closed-shell core, with pairing correlation included, and to establish the M1 sum rule that could be used to validate theoretical and experimental approaches. Possibility to utilize the M1 excitation as a tool to investigate the pairing correlation in medium is also discussed. Method: Three-body model, which consists of a rigid spherical core and two valence nucleons, is employed. Interactions for its two-body subsystems are phenomenologically determined in order to reproduce the two-body and three-body energies. We also derive the M1 sum rule within this three-body picture. Conclusion: The introduced M1 sum rule can be utilized as a benchmark for model calculations of M1 transitions in the systems with two valence nucleons. The total sum of the M1 transition strength is related with the coupled spin of valence nucleons in the open shell, where the pairing correlation is unnegligible. The three-body-model calculations for 18 O, 18 Ne, and 42 Ca nuclei demonstrate a significant effect of the pairing correlations on the low-lying M1 transitions. Therefore, further experimental studies of M1 transitions in those systems are on demand, in order to validate proposed sum rule, provide a suitable probe for the nuclear pairing in medium, as well as to optimize the pairing models.

    Comments:
    10 pages, 3 figures, 4 tables. Revised for re-submission to Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1902.05562 [pdf]
    PRC(2019)·12 citations
  2. 02

    [Submitted on 15 Feb 2019]

    Fock contributions to nuclear symmetry energy and its slope parameter based on Lorentz-covariant decomposition of nucleon self-energies

    Tsuyoshi Miyatsu🇯🇵 · Myung-Ki Cheoun🇰🇷 · Chikako Ishizuka🇯🇵 · K. S. Kim🇰🇷 · Tomoyuki Maruyama🇯🇵 · Koichi Saito🇯🇵

    Using relativistic Hartree-Fock (RHF) approximation, we study the effect of Fock terms on the nuclear properties not only around the saturation density, , but also at higher densities. In particular, we investigate how the momentum dependence due to the exchange contribution affects the nuclear symmetry energy and its slope parameter, using the Lorentz-covariant decomposition of nucleon self-energies in an extended version of the RHF model, in which the exchange terms are adjusted so as to reproduce the single-nucleon potential at . We find that the Fock contribution suppresses the kinetic term of nuclear symmetry energy at the densities around and beyond . It is noticeable that not only the isovector-vector () meson but also the isoscalar mesons () and pion make significant influence on the potential term of nuclear symmetry energy through the exchange diagrams. Furthermore, the exchange contribution prevents the slope parameter from increasing monotonically at high densities.

    Comments:
    35 pages, 13 figures, 5 tables
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1902.05769 [pdf]
    4 citations
  3. 03

    [Submitted on 15 Feb 2019]

    Theoretical calculation of the radiative capture reaction

    Alex Gnech (GSSI, L'Aquila and INFN-PISA)🇮🇹 · Laura Elisa Marcucci (University of Pisa and INFN-PISA)🇮🇹

    We present a new calculation of the radiative capture astrophysical -factor in a cluster model framework. We consider several intercluster potentials, adjusted to reproduce the bound state properties and the elastic scattering phase shifts. Using these potentials, we calculate the astrophysical -factor, obtaining a good agreement with available data, and the photon angular distribution. Finally, we discuss the consequences of a hypothetical resonance-like structure on the -factor.

    Comments:
    27 pages, 9 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1902.05881 [pdf]
    NPA(2019)·18 citations
  4. 04

    [Submitted on 15 Feb 2019]

    Multi-stage jet evolution through QGP using the JETSCAPE framework: inclusive jets, correlations and leading hadrons

    C. Park · A. Angerami · S. A. Bass · S. Cao · J. Coleman · L. Cunqueiro · T. Dai · L. Du · H. Elfner · D. Everett · W. Fan · R. Fries and 32 other authors

    The JETSCAPE Collaboration has recently announced the first release of the JETSCAPE package that provides a modular, flexible, and extensible Monte Carlo event generator. This innovative framework makes it possible to perform a comprehensive study of multi-stage high-energy jet evolution in the Quark-Gluon Plasma. In this work, we illustrate the performance of the event generator for different algorithmic approaches to jet energy loss, and reproduce the measurements of several jet and hadron observables as well as correlations between the hard and soft sector. We also carry out direct comparisons between different approaches to energy loss to study their sensitivity to those observables.

    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1902.05934 [pdf]
    PoS(2019)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE