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Nuclear Theory·nucl-th

Thursday·August 11, 2016

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    [Submitted on 9 Aug 2016]

    Hydrodynamic Predictions for Mixed Harmonic Correlations in 200 GeV Au+Au Collisions

    Fernando G. Gardim🇧🇷 · Frederique Grassi🇧🇷 · Matthew Luzum🇧🇷 · Jacquelyn Noronha-Hostler🇺🇸

    Recent measurements at the LHC involve the correlation of different azimuthal flow harmonics . These new observables add constraints to theoretical models and probe aspects of the system that are independent of the traditional single-harmonic measurements such as 2- and multi-particle cumulants . Many of these new observables have not yet been measured at RHIC, leaving an opportunity to make predictions as a test of models across energies. We make predictions using NeXSPheRIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an important baseline for comparison to correlations of flow harmonics, which contain non-trivial information about the initial state as well as QGP transport properties. We also point out significant biases that can appear when using wide centrality bins and non-trivial event weighting, necessitating care in performing experimental analyses and in comparing theoretical calculations to these measurements.

    Comments:
    10 pages, 9 figures; v2 - updated Fig. 4 to include multiplicity weighing in the Event plane correlations
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1608.02982 [pdf]
    PRC(2017)·52 citations
  2. 02

    [Submitted on 10 Aug 2016]

    Nuclear charge radii: Density functional theory meets Bayesian neural networks

    Raditya Utama · Wei-Chia Chen · Jorge Piekarewicz

    The distribution of electric charge in atomic nuclei is fundamental to our understanding of the complex nuclear dynamics and a quintessential observable to validate nuclear structure models. We explore a novel approach that combines sophisticated models of nuclear structure with Bayesian neural networks (BNN) to generate predictions for the charge radii of thousands of nuclei throughout the nuclear chart. A class of relativistic energy density functionals is used to provide robust predictions for nuclear charge radii. In turn, these predictions are refined through Bayesian learning for a neural network that is trained using residuals between theoretical predictions and the experimental data. Although predictions obtained with density functional theory provide a fairly good description of experiment, our results show significant improvement (better than 40%) after BNN refinement. Moreover, these improved results for nuclear charge radii are supplemented with theoretical error bars. We have successfully demonstrated the ability of the BNN approach to significantly increase the accuracy of nuclear models in the predictions of nuclear charge radii. However, as many before us, we failed to uncover the underlying physics behind the intriguing behavior of charge radii along the calcium isotopic chain.

    Comments:
    14 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1608.03020 [pdf]
    J.Phys.G(2016)·136 citations
  3. 03

    [Submitted on 10 Aug 2016]

    The radiative proton capture on 16O at astrophysical energies

    Sergey Dubovichenko · Albert Dzhazairov-Kakhramanov

    The possibility of description of the experimental data for the astrophysical S-factor of the proton radiative capture on 16O to the ground and first excited states of 17F was considered in the frame of the modified potential cluster model with forbidden states and classification of the states according to Young tableaux. It was shown that on the basis of the E1 transitions from the P states of p16O scattering to the bound states of 17F in the p16O channel, it generally succeed to explain the value of measured astrophysical S-factors and reaction rates at astrophysical energies.

    Comments:
    9p., 4 fig., 2 tabl., 54 ref
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1608.03103 [pdf]
    Indian Journal of Physics 2018. V.92. P.9…·1 citation
  4. 04

    [Submitted on 8 Aug 2016]

    Event-shape-engineering study of charge separation in heavy-ion collisions

    Fufang Wen🇺🇸 · Jacob Bryon🇺🇸 · Liwen Wen🇺🇸 · Gang Wang🇺🇸

    Recent measurements of charge-dependent azimuthal correlations in high-energy heavy-ion collisions have indicated charge-separation signals perpendicular to the reaction plane, and have been related to the chiral magnetic effect (CME). However, the correlation signal is contaminated with the background caused by the collective motion (flow) of the collision system, and an effective approach is needed to remove the flow background from the correlation. We present a method study with simplified Monte Carlo simulations and a multi-phase transport model, and develop a scheme to reveal the true CME signal via the event-shape engineering with the flow vector of the particles of interest.

    Comments:
    6 pages, 8 figures, to be published in Chinese Physics C
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1608.03205 [pdf]
    CPC(2018)·42 citations
  5. 05

    [Submitted on 9 Aug 2016] (cross-list from astro-ph.HE)

    Millihertz Quasi-periodic Oscillations in 4U 1636-536: Putting Possible Constraints on the Neutron Star Size

    H. Stiele · W. Yu · A. K. H. Kong

    Based on previous studies of quasi-periodic oscillations in neutron star LMXBs, mHz quasi-periodic oscillations (QPO) are believed to be related to `marginally stable' burning on the neutron star (NS) surface. Our study of phase resolved energy spectra of these oscillations in 4U 1636-53 shows that the oscillations are not caused by variations in the blackbody temperature of the neutron star, but reveals a correlation between the change of the count rate during the mHz QPO pulse and the spatial extend of a region emitting blackbody emission. The maximum size of the emission area km, provides the direct evidence that the oscillations originate from a variable surface area constrained on the NS and are therefore not related to instabilities in the accretion disk. The obtained lower limit on the size of the neutron star (11.0 km) rules out equations of state that prefer small NS radii. Observations of mHz QPOs in NS LMXBs with NICER and eXTP will reduce the statistical uncertainty in the lower limit on the NS radius, which together with better estimates of the hardening factor and distance, will allow improving discrimination between different equations of state and compact star models. Furthermore, future missions will allow us to measure the peak blackbody emission area for a single mHz QPO pulse, which will push the lower limit to larger radii.

    Comments:
    10 pages, 4 figures, accepted for publication in ApJ
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
    arXiv:
    1608.02947 [pdf]
    ApJ(2016)·17 citations
  6. 06

    [Submitted on 10 Aug 2016] (cross-list from nucl-ex)

    Recent Experimental Results on Nuclear Cluster Physics

    C. Beck (IPHC Strasbourg)🇫🇷

    Knowledge on nuclear cluster physics has increased considerably since the pioneering discovery of 12C+12C resonances half a century ago and nuclear clustering remains one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. The occurrence of "exotic" shapes and/or Bose-Einstein alpha condensates in light N-Z alpha-conjugate nuclei is investigated. Evolution of clustering from stability to the drip-lines examined with clustering aspects persisting in light neutron-rich nuclei is consistent with the extension of the "Ikeda-diagram" to non alpha-conjugate nuclei.

    Comments:
    14 pages, 2 figures, extended version of the written contribution (6 pages) of the introductory talk given at the CLUSTER '16 Conference held in May 2016 in Napoli, Italy which Proceedings will be published in J. Phys. Conferences Series. arXiv admin note: substantial text overlap with arXiv:1408.0684, arXiv:1603.02574, arXiv:1402.6590, arXiv:1303.0960
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1608.03190 [pdf]
    J.Phys.Conf.Ser.(2017)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE