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Nuclear Theory·nucl-th

Tuesday·August 28, 2018

4 papers—2 primary·2 cross-listed

All4Primary2Cross-lists2
  1. 01

    [Submitted on 24 Aug 2018]

    Directed flow in an extended multiphase transport model

    Chong-Qiang Guo🇨🇳 · He Liu🇨🇳 · Jun Xu🇨🇳

    We have studied the rapidity-odd directed flow in Au+Au collisions in the beam energy range from = 7.7 to 39 GeV within the framework of an extended multiphase transport model with both partonic and hadronic mean-field potentials incorporated. Effects of the partonic scatterings, mean-field potentials, hadronization, and hadronic evolution on the directed flow are investigated, and it is found that the final directed flow is mostly sensitive to the partonic scatterings and the hadronization mechanism. Our study shows that a negative slope of the proton directed flow does not necessarily need the equation of state with a first-order phase transition.

    Comments:
    7 pages, 7 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex)
    arXiv:
    1808.08334 [pdf]
    PRC(2018)·9 citations
  2. 02

    [Submitted on 27 Aug 2018]

    Validity of the distorted-wave impulse-approximation description of CaK data using only ingredients from a nonlocal dispersive optical model

    M. C. Atkinson · H.P. Blok · L. Lapikás · R. J. Charity · W. H. Dickhoff

    The nonlocal implementation of the dispersive optical model (DOM) provides all the ingredients for distorted-wave impulse-approximation (DWIA) calculations of the reaction. It provides both the overlap function, including its normalization, and the outgoing proton distorted wave. This framework is applied to describe the knockout of a proton from the and orbitals in Ca with fixed normalizations of 0.71 and 0.60, respectively. Data were obtained in parallel kinematics for three outgoing proton energies: 70, 100, and 135 MeV. Agreement with the data is as good as, or better than, previous descriptions employing local optical potentials and overlap functions from Woods-Saxon potentials - both with standard nonlocality corrections - whose normalization (spectroscopic factor) and radius were fitted to the data. The present analysis suggests that slightly larger spectroscopic factors are obtained when nonlocal optical potentials are employed than those generated with local potentials. The results further suggest that the chosen kinematical window around 100 MeV proton energy provides the best and cleanest method to employ the DWIA for the analysis of this reaction. The conclusion that substantial ground-state correlations cannot be ignored when describing a closed-shell atomic nucleus is therefore confirmed in detail. To reach these conclusions, it is essential to have a complete description of the nucleon single-particle propagator that accounts for all elastic nucleon-scattering observables in a wide energy domain up to 200 MeV. The current nonlocal implementation of the DOM fulfills this requirement.

    Comments:
    15 pages, 11 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1808.08895 [pdf]
    PRC(2018)·33 citations
  3. 03

    [Submitted on 27 Aug 2018] (cross-list from hep-lat)

    Proton Mass Decomposition from the QCD Energy Momentum Tensor

    Yi-Bo Yang🇺🇸 · Jian Liang🇺🇸 · Yu-Jiang Bi🇨🇳 · Ying Chen🇨🇳 · Terrence Draper🇺🇸 · Keh-Fei Liu🇺🇸 · Zhaofeng Liu🇨🇳

    We report results on the proton mass decomposition and also on related quark and glue momentum fractions. The results are based on overlap valence fermions on four ensembles of DWF configurations with three lattice spacings and three volumes, and several pion masses including the physical pion mass. With fully non-perturbative renormalization (and universal normalization on both quark and gluon), we find that the quark energy and glue field energy contribute 33(4)(4)\% and 37(5)(4)\% respectively in the scheme at GeV. A quarter of the trace anomaly gives a 23(1)(1)\% contribution to the proton mass based on the sum rule, given 9(2)(1)\% contribution from the and quark scalar condensates. The and glue momentum fractions in the scheme are in good agreement with global analyses at GeV.

    Comments:
    10 pages, 6 figures
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1808.08677 [pdf]
    PRL(2018)·224 citations
  4. 04

    [Submitted on 27 Aug 2018] (cross-list from hep-ph)

    On coupled-channel dynamics in the presence of anomalous thresholds

    M.F.M. Lutz🇩🇪 · C.L. Korpa🇭🇺

    We explore a general framework how to treat coupled-channel systems in the presence of overlapping left and right-hand cuts as well as anomalous thresholds. Such systems are studied in terms of a generalized potential, where we exploit the known analytic structure of t- and u-channel forces as the exchange masses get smaller approaching their physical values. Given an approximate generalized potential the coupled-channel reaction amplitudes are defined in terms of non-linear systems of integral equations. For large exchange masses, where there are no anomalous thresholds present, conventional methods are applicable to derive numerical solutions to the latter. At a formal level a generalization to the anomalous case is readily formulated by use of suitable contour integrations with amplitudes to be evaluated at complex energies. However, it is a considerable challenge to find numerical solutions to anomalous systems set up on a set of complex contours. By a suitable deformations of left-hand and right-hand cut lines we managed to establish a framework of linear integral equations defined for real energies. Explicit expressions are derived for the driving terms that hold for an arbitrary number of channels. Our approach is illustrated in terms of a schematic 3-channel systems. It is demonstrated that despite the presence of anomalous thresholds the scattering amplitude can be represented in terms of 3 phase shifts and 3 in-elasticity parameters, as one would expect from the coupled-channel unitarity condition.

    Comments:
    49 pages, 17 figures, major revision of the published version, the updated framework is applicable also in the presence of overlapping anomalous cut structures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    1808.08695 [pdf]
    PRD(2018)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE