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Nuclear Theory·nucl-th

Monday·May 31, 2021

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    [Submitted on 27 May 2021]

    Implications of PREX-2 on the electric dipole polarizability of neutron rich nuclei

    J. Piekarewicz

    The recent announcement by the PREX collaboration of an unanticipated thick neutron skin in 208Pb (Rskin208) has challenged our understanding of neutron rich matter in the vicinity of nuclear saturation density. Whereas earlier constraints indicate that the symmetry energy is relatively soft, the PREX-2 result seems to suggest the opposite. We confront constraints on the symmetry energy obtained from measurements of the electric dipole polarizability against those informed by the PREX-2 measurement of Rskin208 and by the correlations that it entails. Covariant energy density functionals informed by the properties of finite nuclei are used to compute the electric dipole response of 48Ca, 68Ni, 132Sn, and 208Pb. The set of functionals used in this work are consistent with experimental data, yet are flexible enough in that they span a wide range of values of Rskin208. It is found that theoretical predictions of the electric dipole polarizability that are consistent with the PREX-2 measurement systematically overestimate the corresponding values extracted from the direct measurements of the distribution of electric dipole strength. The neutron skin thickness of 208Pb extracted from parity violating electron scattering and the electric dipole polarizability measured in photoabsorption experiments are two of the cleanest experimental tools used to constrain the symmetry energy around nuclear saturation density. However, the recent value of Rskin208 that suggests a fairly stiff symmetry energy stands in stark contrast to the conclusions derived from the electric dipole polarizability. At present, we offer no solution to this dilemma.

    Comments:
    11 pages and 9 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2105.13452 [pdf]
    PRC(2021)·59 citations
  2. 02

    [Submitted on 27 May 2021]

    Hyperon Polarization from the Vortical Fluid in Low Energy Nuclear Collisions

    Yu Guo🇨🇳 · Jinfeng Liao🇺🇸 · Enke Wang🇨🇳 · Hongxi Xing🇨🇳 · Hui Zhang🇨🇳

    In 2017, STAR Collaboration reported the measurements of hyperon global polarization in heavy ion collisions, suggesting the subatomic fireball fluid created in these collisions as the most vortical fluid. There remains the interesting question: at which beam energy the truly most vortical fluid will be located. In this work we perform a systematic study on the beam energy dependence of hyperon global polarization phenomenon, especially in the interesting region. We find a non-monotonic trend, with the global polarization to first increase and then decrease when beam energy is lowered from down to . The maximum polarization signal has been identified around , where the heavy ion collisions presumably create the most vortical fluid. Detailed experimental measurements in the beam energy region are expected to test the prediction very soon.

    Comments:
    5 pages, 4 figures, new results for hyperon local polarization are added
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    2105.13481 [pdf]
    PRC(2021)·57 citations
  3. 03

    [Submitted on 28 May 2021]

    Baryon number in proton-proton and proton-nucleus high energy collisions

    Marek Jeżabek🇵🇱 · Andrzej Rybicki🇵🇱

    New analyses of baryon spectra in proton-proton and proton-carbon collisions at GeV, made in the framework of two phenomenological models are presented. The first model in question is the classic Dual Parton Model by Capella and Tran Thanh Van, the second is the Gluon Exchange Model very recently proposed by the authors. For both studies, the usage of modern experimental data from the CERN SPS eliminates several of the most important limitations inherent to earlier studies of this type. In both studies, the standard mechanism of baryon stopping with preservation of the diquark, proposed by Capella and Tran Thanh Van fails to describe the distribution of non-strange baryons in collisions of the projectile proton with {\em more than one} nucleon from the carbon target obtained from experimental data, and the upper limit for the contribution of this mechanism can be established. In both cases, the conclusion is that the projectile diquark must be very often disintegrated. This opens new diagrams not available in proton-proton collisions which lead to the transport of baryon number over long distances in rapidity. The present limitations, and possibility of improvement in both approaches are discussed. The implications of our findings for new measurements are addressed, in particular using antiproton beams.

    Comments:
    21 pages, 14 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2105.13741 [pdf]
    Eur.Phys.J.Plus(2021)·9 citations
  4. 04

    [Submitted on 28 May 2021]

    Short-range correlation physics at low RG resolution

    A. J. Tropiano🇺🇸 · S. K. Bogner🇺🇸 · R. J. Furnstahl🇺🇸

    Recent experiments have succeeded in isolating processes for which short-range correlation (SRC) physics is dominant and well accounted for by SRC phenomenology. But an alternative and compelling picture emerges from renormalization group (RG) evolution to low RG resolution. At high RG resolution, SRCs are identified as components in the nuclear wave function with relative pair momenta greater than the Fermi momentum. Scale separation results in wave-function factorization that can be exploited with phenomenologies such as the generalized contact formalism or the low-order correlation operator approximation. Evolution to lower resolution shifts SRC physics from nuclear structure to the reaction operators without changing the measured observables. We show how the features of SRC phenomenology manifested at high RG resolution are cleanly identified at low RG resolution using simple two-body operators and local-density approximations with uncorrelated wave functions, all of which can be systematically generalized. We verify that the experimental consequences to date follow directly at low resolution from well-established properties of nucleon-nucleon interactions such as the tensor force. Thus the RG reconciles the contrasting pictures of the same experiment and shows how to get correct results using wave functions without SRC components. Our demonstration has implications for the analysis of knock-out reactions for which SRC physics is not cleanly isolated.

    Comments:
    18 pages, 10 figures. Updated figures 5 and 10
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2105.13936 [pdf]
    PRC(2021)·50 citations

Affiliations

first authorsco-authorsvia INSPIRE