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Nuclear Theory·nucl-th

Monday·March 5, 2018

6 papers—6 primary·0 cross-listed

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  1. 01

    [Submitted on 1 Mar 2018]

    Distribution of Magnetic Dipole Strength -Binning

    Arun Kingan · Mingyang Ma · Larry Zamick

    In previous works we examined the systematics of magnetic dipole transitions in a single j shell. We here extend the study to large space calculations. We consider Ti and Cr isotopes.. In this work we focus on the B(M1) strength as a function of excitation of energy. The initial state is the lowest J= state. T=1 state in a specified nucleus. The final states are J=0 T=2 , all in one plot, and J=2 T=2 in another. The initial figures have points all over the map although there is a suggestion of an exponential trend. To reduce clutter we perform binning operations in which the summed strength in a given energy interval is represented by a single point. The new binning curves show more clearly the exponential fall of B(M1)'s with energy.

    Comments:
    arXiv admin note: substantial text overlap with arXiv:1707.00266
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1803.00645 [pdf]
    IJMPE(2020)·5 citations
  2. 02

    [Submitted on 1 Mar 2018]

    Beta equilibrium in neutron star mergers

    Mark G. Alford🇺🇸 · Steven P. Harris🇺🇸

    We show that the commonly used criterion for beta equilibrium in neutrino-transparent dense nuclear matter becomes invalid as temperatures rise above 1 MeV. Such temperatures are attained in neutron star mergers. By numerically computing the relevant weak interaction rates we find that the correct criterion for beta equilibrium requires an isospin chemical potential that can be as large as 10-20 MeV, depending on the temperature at which neutrinos become trapped.

    Comments:
    Section on neutrino mean free paths added. Discussion and plot of effect of isospin chemical potential on beta-equilibrium proton fraction added
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1803.00662 [pdf]
    PRC(2018)·108 citations
  3. 03

    [Submitted on 2 Mar 2018]

    Inclusive electron-nucleus cross section within the Self Consistent Green's Function approach

    N. Rocco🇬🇧 · C. Barbieri🇬🇧

    We compute inclusive electron-nucleus cross sections using ab initio spectral functions of He and O obtained within the Self Consistent Green's Function approach. The formalism adopted is based on the factorization of the spectral function and the nuclear transition matrix elements. This allows to provide an accurate description of nuclear dynamics and to account for relativistic effects in the interaction vertex. Our calculations use a saturating chiral Hamiltonian in order reproduce the correct nuclear sizes. When final state interactions for the struck particle are accounted for, we find nice agreement between the data and the theory for the inclusive electron-O cross section. The results lay the foundations for future applications of the Self Consistent Green's Function method, in both closed and open shell nuclei, to neutrino data analysis. This work also presents results for the point-proton, charge and single-nucleon momentum distribution of the same two nuclei. The center of mass can affect these quantities for light nuclei and cannot be separated cleanly in most ab initio post-Hartree-Fock methods. In order to address this, we developed a Metropolis Monte Carlo calculation in which the center of mass coordinate can be subtracted exactly from the trial wave function and the expectation values. We gauged this effect for He by removing the center of mass effect from the Optimal Reference State wave function that is generated during the Self Consistent Green's Function calculations. Our findings clearly indicate that the residual center of mass contribution strongly modifies calculated matter distributions with respect to those obtained in the intrinsic frame. Hence, its subtraction is crucial for a correct description of light nuclei.

    Comments:
    12 pages, 10 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex)
    arXiv:
    1803.00825 [pdf]
    PRC(2018)·33 citations
  4. 04

    [Submitted on 2 Mar 2018]

    Probing vorticity structure in heavy-ion collisions by local polarization

    Xiao-Liang Xia🇨🇳 · Hui Li🇨🇳 · Zebo Tang🇨🇳 · Qun Wang🇨🇳

    We study the local structure of the vorticity field and the polarization in Au+Au collisions in the energy range -- GeV and Pb+Pb collisions at GeV using A Multi-Phase Transport (AMPT) model. We focus on the vorticity field arising from the non-uniform expansion of the fireball, which gives the circular structure of the transverse vorticity around the direction as well as the quadrupole pattern of the longitudinal vorticity in the transverse plane. As a consequence, the three components of the polarization vector for hyperons show harmonic behaviors as , , and , where and are the azimuthal angle and rapidity in momentum space. These patterns of the local polarization are expected to be tested in future experiments.

    Comments:
    8 pages, 7 figures. One table, one figure and references added. Discussions in Sec III and IV improved. To appear in Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1803.00867 [pdf]
    PRC(2018)·207 citations
  5. 05

    [Submitted on 2 Mar 2018]

    Estimating model bias over the complete nuclide chart with sparse Gaussian processes at the example of INCL/ABLA and double-differential neutron spectra

    Georg Schnabel🇫🇷

    Predictions of nuclear models guide the design of nuclear facilities to ensure their safe and efficient operation. Because nuclear models often do not perfectly reproduce available experimental data, decisions based on their predictions may not be optimal. Awareness about systematic deviations between models and experimental data helps to alleviate this problem. This paper shows how a sparse approximation to Gaussian processes can be used to estimate the model bias over the complete nuclide chart at the example of inclusive double-differential neutron spectra for incident protons above 100\,MeV. A powerful feature of the presented approach is the ability to predict the model bias for energies, angles, and isotopes where data are missing. The number of experimental data points that can be taken into account is at least in the order of magnitude of~ thanks to the sparse approximation. The approach is applied to the Liège Intranuclear Cascade Model (INCL) coupled to the evaporation code ABLA. The results suggest that sparse Gaussian process regression is a viable candidate to perform global and quantitative assessments of models. Limitations of a philosophical nature of this (and any other) approach are also discussed.

    Subjects:
    Nuclear Theory (nucl-th); Data Analysis, Statistics and Probability (physics.data-an)
    arXiv:
    1803.00928 [pdf]
    EPJ Nuclear Sci.Technol.(2018)·5 citations
  6. 06

    [Submitted on 2 Mar 2018]

    Fitting and Analysis Technique for Inconsistent Nuclear Data

    Georg Schnabel🇫🇷

    Consistent experiment data are crucial to adjust parameters of physics models and to determine best estimates of observables. However, often experiment data are not consistent due to unrecognized systematic errors. Standard methods of statistics such as -fitting cannot deal with this case. Their predictions become doubtful and associated uncertainties too small. A human has then to figure out the problem, apply corrections to the data, and repeat the fitting procedure. This takes time and potentially costs money. Therefore, a Bayesian method is introduced to fit and analyze inconsistent experiment data. It automatically detects and resolves inconsistencies. Furthermore, it allows to extract consistent subsets from the data. Finally, it provides an overall prediction with associated uncertainties and correlations less prone to the common problem of too small uncertainties. The method is foreseen to function with a large corpus of data and hence may be used in nuclear databases to deal with inconsistencies in an automated fashion.

    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex); Data Analysis, Statistics and Probability (physics.data-an)
    arXiv:
    1803.00960 [pdf]
    8 citations

Affiliations

first authorsco-authorsvia INSPIRE