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Nuclear Theory·nucl-th

Monday·September 3, 2018

7 papers—4 primary·3 cross-listed

All7Primary4Cross-lists3
  1. 01

    [Submitted on 30 Aug 2018]

    Hidden charm pentaquarks: mass spectrum, magnetic moments, and photocouplings

    Emmanuel Ortiz-Pacheco🇲🇽 · Roelof Bijker🇲🇽 · César Fernández-Ramírez🇲🇽

    We develop an extension of the usual three flavor quark model to four flavors (u, d, s and c), and discuss the classification of pentaquark states with hidden charm. We fit our model to the known baryon spectrum and we predict the double and triple charm baryons, finding good agreement with the most recent lattice QCD calculations. We compute the the ground state of hidden charm pentaquarks and their associated magnetic moments and electromagnetic couplings, of interest to pentaquark photoproduction experiments.

    Comments:
    21 pages, 5 figures, 14 tables, modified version, Journal of Physics G, in press
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1808.10512 [pdf]
    J.Phys.G(2019)·52 citations
  2. 02

    [Submitted on 30 Aug 2018]

    Nuclear kinetic density from ab initio theory

    M. Gennari🇨🇦 · P. Navratil🇨🇦

    Background: The nuclear kinetic density is one of many fundamental quantities in density functional theory (DFT) dependent on the nonlocal nuclear density. Often, approximations may be made when computing the density that may result in spurious contributions in other DFT quantities. With the ability to compute the nonlocal nuclear density from ab initio wave functions, it is now possible to estimate effects of such spurious contributions. Purpose: We derive the kinetic density using ab initio nonlocal scalar one-body nuclear densities computed within the no-core shell model (NCSM) approach, utilizing two- and three-nucleon chiral interactions as the sole input. With the ability to compute translationally invariant nonlocal densities, it is possible to directly gauge the impact of the spurious center-of-mass (COM) contributions in DFT quantities such as the kinetic density. Methods: The nonlocal nuclear densities are derived from the NCSM one-body densities calculated in second quantization. We present a review of COM contaminated and translationally invariant nuclear densities. We then derive an analytic expression for the kinetic density using these nonlocal densities, producing an ab initio kinetic density. Results: The ground state nonlocal densities of \textsuperscript{4,6,8}He, \textsuperscript{12}C, and \textsuperscript{16}O are used to compute the kinetic densities of the aforementioned nuclei. The impact of the COM removal technique in the densities is discussed. The results of this work can be extended to other fundamental quantities in DFT. Conclusions: The use of a general nonlocal density allows for the calculation of fundamental quantities taken as input in theories such as DFT. This allows benchmarking of procedures for COM removal in different many-body techniques.

    Comments:
    14 pages, 17 figures. Version accepted for publication
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1808.10537 [pdf]
    PRC(2019)·5 citations
  3. 03

    [Submitted on 31 Aug 2018]

    Two-particle angular correlations in pp and p-Pb collisions at LHC energies from a multi-phase transport model

    Liuyao Zhang🇨🇳 · Jinhui Chen🇨🇳 · Ziwei Lin🇨🇳 · Yugang Ma🇨🇳 · Song Zhang🇨🇳

    We apply a multi-phase transport (AMPT) model to study two-particle angular correlations in collisions at TeV. Besides being able to describe the angular correlation functions of meson-meson pairs, a large improvement for the angular correlations of baryon-baryon and antibaryon-antibaryon is achieved. We further find that the AMPT model with new quark coalescence provides an even better description on the anti-correlation feature of baryon-baryon correlations observed in the experiments. We also extend the study to p-Pb collisions at TeV and obtained similar results. These results help us better understand the particle production mechanism in and p-Pb collisions at LHC energies.

    Comments:
    12 pages, 9 figures, submit for publication
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1808.10641 [pdf]
    PRC(2018)·21 citations
  4. 04

    [Submitted on 31 Aug 2018]

    The influence of tensor force on the microscopic heavy-ion interaction potential

    Lu Guo · K. Godbey · A. S. Umar

    Background: The tensor interaction is known to play an important role in the nuclear structure studies of exotic nuclei. However, most microscopic studies of low-energy nuclear reactions neglect the tensor force, resulting in a lack of knowledge concerning the effect of the tensor force on HIC...... Purpose: The theoretical study of the influence of the tensor force on heavy-ion interaction potentials is required to further our understanding of the microscopic mechanisms entailed in fusion dynamics. Method: The full Skyrme tensor force is implemented into the static Hartree-Fock and dynamic density-constrained time-dependent Hartree-Fock (DC-TDHF) theory to calculate both static (frozen density) and dynamic microscopic interaction potentials for reactions involving exotic and stable nuclei. Results: The static potentials are found to be systematically higher than the dynamical results, which are attributed to the microscopic dynamical effects included in TDHF. We also show that the dynamical potential barriers vary more significantly by the inclusion of tensor force than the static barriers. The influence of isoscalar and isovector tensor terms is also investigated with the TIJ set of forces. For light systems, the tensor force is found to have an imperceptible effect on the nucleus-nucleus potential. However, for medium and heavy spin-unsaturated reactions, the potentials may change from a fraction of an MeV to almost 2 MeV by the inclusion of tensor force, indicating a strong impact of the tensor force on sub-barrier fusion. Conclusions: The tensor force could indeed play a large role in the fusion of nuclei, with spin-unsaturated systems seeing a systematic increase in ion-ion barrier height and width. This fusion hindrance is partly due to static, ground state effects from the inclusion of the tensor force, though additional hindrance appears when studying nuclear dynamics.

    Comments:
    accepted for publication in Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1808.10683 [pdf]
    PRC(2018)·33 citations
  5. 05

    [Submitted on 30 Aug 2018] (cross-list from astro-ph.HE)

    Fingerprints of heavy element nucleosynthesis in the late-time lightcurves of kilonovae

    Meng-Ru Wu🇹🇼 · Jennifer Barnes🇺🇸 · Gabriel Martinez-Pinedo🇩🇪 · Brian D. Metzger🇺🇸

    The kilonova emission observed following the binary neutron star merger event GW170817 provided the first direct evidence for the synthesis of heavy nuclei through the r-process. The late-time transition in the spectral energy distribution to near-infrared wavelengths was interpreted as indicating the production of lanthanide nuclei, with atomic mass number A>140. However, compelling evidence for the presence of heavier third-peak r-process elements (e.g., gold, platinum) or translead nuclei remains elusive. At early times (~days) most of the r-process heating arises from a large statistical ensemble of beta-decays, which thermalize efficiently while the ejecta is still dense, generating a heating rate that is reasonably approximated by a single power-law. However, at later times (weeks to months), the decay energy input can possibly be dominated by a discrete number of alpha-decays, 223Ra (half-life t_{1/2}=11.43d), 225Ac (t_{1/2}=10.0d, following the beta-decay of 225Ra with t_{1/2}=14.9d), and the fissioning isotope 254Cf (t_{1/2}=60.5d), which liberate more energy per decay and thermalize with greater efficiency than beta-decay products. Late-time nebular observations of kilonovae which constrain the radioactive power provide the potential to identify signatures of these individual isotopes, thus confirming the production of heavy nuclei. In order to constrain the bolometric light to the required accuracy, multi-epoch & wide-band observations are required with sensitive instruments like the James Webb Space Telescope. In addition, by comparing the nuclear heating rate obtained with an abundance distribution following the Solar r abundance pattern, to the bolometric lightcurve of AT2017gfo, we find that the yet-uncertain r abundance of 72Ge plays a decisive role in powering the lightcurve, if one assumes that GW170817 has produced a full range of the Solar r abundances down to A~70.

    Comments:
    11 pages, 8 figures including supplemental material, accepted by PRL
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
    arXiv:
    1808.10459 [pdf]
    PRL(2019)·120 citations
  6. 06

    [Submitted on 31 Aug 2018] (cross-list from astro-ph.HE)

    Accretion heated atmospheres of X-ray bursting neutron stars

    V.F. Suleimanov🇩🇪 · J. Poutanen🇷🇺 · K. Werner🇩🇪

    Some thermonuclear (type I) X-ray bursts at the neutron star surfaces in low-mass X-ray binaries take place during hard persistent states of the systems. Spectral evolution of these bursts is well described by the atmosphere model of a passively cooling neutron star when the burst luminosity is high enough. The observed spectral evolution deviates from the model predictions when the burst luminosity drops below a critical value of 20-70% of the maximum luminosity. We suggest that these deviations are induced by the additional heating of the accreted particles. We present a method for computation of the neutron star atmosphere models heated by accreted particles assuming that their energy is released via Coulomb interactions with electrons. We compute the temperature structures and the emergent spectra of the atmospheres of various chemical compositions and investigate the dependence of the results on the other model parameters. We show that the heated atmosphere develops the hot (20--100 keV) corona-like surface layer cooled by Compton scattering, and the deeper, almost isothermal optically thick region with a temperature of a few keV. The emergent spectra deviate strongly from those of undisturbed neutron star atmospheres, with the main differences being the presence of a high-energy tail and a strong excess in the low-energy part of the spectrum. They also lack the iron absorption edge, which is visible in the spectra of undisturbed low-luminosity atmospheres with solar chemical composition. Using the computed spectra, we obtained the dependences of the dilution and color-correction factors as functions of relative luminosities for pure helium and solar abundance atmospheres. We show that the helium model atmosphere heated by accretion corresponding to 5% of the Eddington luminosity describes well the late stages of the X-ray bursts in 4U 1820-30.

    Comments:
    14 pages, 19 figures, published version, some misprints were fixed
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    1808.10655 [pdf]
    Astron.Astrophys.(2018)·30 citations
  7. 07

    [Submitted on 31 Aug 2018] (cross-list from hep-ph)

    Accessing gluon parton distributions in large momentum effective theory

    Jian-Hui Zhang🇩🇪 · Xiangdong Ji🇺🇸 · Andreas Schäfer🇩🇪 · Wei Wang🇨🇳 · Shuai Zhao🇨🇳

    Gluon parton distribution functions (PDFs) in the proton can be calculated directly on Euclidean lattices using large momentum effective theory (LaMET). To realize this goal, one has to find renormalized gluon quasi-PDFs in which power divergences and operator mixing are thoroughly understood. For the unpolarized distribution, we identify four independent quasi-PDF correlators that can be multiplicatively renormalized on the lattice. Similarly, the helicity distribution can be derived from three independent multiplicatively renormalizable quasi-PDFs. We provide a LaMET factorization formula for these renormalized quasi-PDFs from which one can extract the gluon PDFs.

    Comments:
    5 pages, version accepted by Phys. Rev. Lett
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1808.10824 [pdf]
    PRL(2019)·122 citations

Affiliations

first authorsco-authorsvia INSPIRE