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Nuclear Theory·nucl-th

Monday·September 18, 2017

10 papers—3 primary·7 cross-listed

All10Primary3Cross-lists7
  1. 04

    Central and peripheral interactions of hadrons

    I.M. Dremin🇷🇺 · V.A. Nechitailo🇷🇺 · S.N. White🇨🇭

    Surprisingly enough, the ratio of elastic to inelastic cross sections of proton interactions increases with energy in the interval correspond- ing to ISR - LHC (i.e. from 10 GeV to 10 TeV). That leads to special features of their spatial interaction region at these and higher ener- gies. Within the framework of some phenomenological models, we show how the particular ranges of the transferred momenta measured in elastic scattering experiments expose the spatial features of the in- elastic interaction region according to the unitarity condition. The difference between their predictions at higher energies is discussed. The notion of central and peripheral collisions of hadrons is treated in terms of the impact parameters description. It is shown that the shape of the differential cross section in the diffraction cone is mostly determined by collisions with intermediate impact parameters. Elastic scattering at very small transferred momenta is sensitive to peripheral processes with large impact parameters. The role of central collisions in formation of the diffraction cone is less significant.

    ↳ hep-phhep-exnucl-exnucl-thEPJC(2017)·9 citations
  2. 05

    The Structure of the Proton in the LHC Precision Era

    Jun Gao🇨🇳 · Lucian Harland-Lang🇬🇧 · Juan Rojo🇳🇱

    We review recent progress in the determination of the parton distribution functions (PDFs) of the proton, with emphasis on the applications for precision phenomenology at the Large Hadron Collider (LHC). First of all, we introduce the general theoretical framework underlying the global QCD analysis of the quark and gluon internal structure of protons. We then present a detailed overview of the hard-scattering measurements, and the corresponding theory predictions, that are used in state-of-the-art PDF fits. We emphasize here the role that higher-order QCD and electroweak corrections play in the description of recent high-precision collider data. We present the methodology used to extract PDFs in global analyses, including the PDF parametrization strategy and the definition and propagation of PDF uncertainties. Then we review and compare the most recent releases from the various PDF fitting collaborations, highlighting their differences and similarities. We discuss the role that QED corrections and photon-initiated contributions play in modern PDF analysis. We provide representative examples of the implications of PDF fits for high-precision LHC phenomenological applications, such as Higgs coupling measurements and searches for high-mass New Physics resonances. We conclude this report by discussing some selected topics relevant for the future of PDF determinations, including the treatment of theoretical uncertainties, the connection with lattice QCD calculations, and the role of PDFs at future high-energy colliders beyond the LHC.

    ↳ hep-phhep-exhep-latnucl-ex+1Phys.Rept.(2018)·313 citations
  3. 06

    Matching the Quasi Parton Distribution in a Momentum Subtraction Scheme

    Iain W. Stewart🇺🇸 · Yong Zhao🇺🇸

    The quasi parton distribution is a spatial correlation of quarks or gluons along the direction in a moving nucleon which enables direct lattice calculations of parton distribution functions. It can be defined with a nonperturbative renormalization in a regularization independent momentum subtraction scheme (RI/MOM), which can then be perturbatively related to the collinear parton distribution in the scheme. Here we carry out a direct matching from the RI/MOM scheme for the quasi-PDF to the PDF, determining the non-singlet quark matching coefficient at next-to-leading order in perturbation theory. We find that the RI/MOM matching coefficient is insensitive to the ultraviolet region of convolution integral, exhibits improved perturbative convergence when converting between the quasi-PDF and PDF, and is consistent with a quasi-PDF that vanishes in the unphysical region as the proton momentum , unlike other schemes. This direct approach therefore has the potential to improve the accuracy for converting quasi-distribution lattice calculations to collinear distributions.

    ↳ hep-phhep-latnucl-thPRD(2018)·152 citations
  4. 07

    Integral transforms of the quantum mechanical path integral: hit function and path averaged potential

    James P. Edwards🇲🇽 · Urs Gerber🇲🇽 · Christian Schubert🇲🇽 · Maria Anabel Trejo🇩🇪 · Axel Weber🇲🇽

    We introduce two new integral transforms of the quantum mechanical transition kernel that represent physical information about the path integral. These transforms can be interpreted as probability distributions on particle trajectories measuring respectively the relative contribution to the path integral from paths crossing a given spatial point (the hit function) and the likelihood of values of the line integral of the potential along a path in the ensemble (the path averaged potential).

    ↳ quant-phhep-thnucl-thphysics.atom-phPRE(2018)·9 citations
  5. 08

    Octet Baryons in Large Magnetic Fields

    Amol Deshmukh🇺🇸 · Brian C. Tiburzi🇺🇸

    Magnetic properties of octet baryons are investigated within the framework of chiral perturbation theory. Utilizing a power counting for large magnetic fields, the Landau levels of charged mesons are treated exactly giving rise to baryon energies that depend non-analytically on the strength of the magnetic field. In the small-field limit, baryon magnetic moments and polarizabilities emerge from the calculated energies. We argue that the magnetic polarizabilities of hyperons provide a testing ground for potentially large contributions from decuplet pole diagrams. In external magnetic fields, such contributions manifest themselves through decuplet-octet mixing, for which possible results are compared in a few scenarios. These scenarios can be tested with lattice QCD calculations of the octet baryon energies in magnetic fields.

    ↳ hep-phhep-latnucl-thPRD(2018)·22 citations
  6. 09

    Constraining the Mass and Radius of Neutron Stars in Globular Clusters

    A.W. Steiner (1,2)🇺🇸 · C.O. Heinke (3)🇨🇦 · S. Bogdanov (4)🇺🇸 · C. Li (3,5)🇨🇦 · W.C.G. Ho (6)🇬🇧 · A. Bahramian (3,7)🇨🇦 · S. Han (1) ((1) Tennessee U., (2) Oak Ridge Natl. Lab., Phys. Div. (3) U. of Alberta, (4) Columbia, (5) CAS, IHEP, Beijing (6) U. of Southampton, (7) Michigan State U.)🇺🇸

    We analyze observations of eight quiescent low-mass X-ray binaries in globular clusters and combine them to determine the neutron star mass-radius curve and the equation of state of dense matter. We determine the effect that several uncertainties may have on our results, including uncertainties in the distance, the atmosphere composition, the neutron star maximum mass, the neutron star mass distribution, the possible presence of a hotspot on the neutron star surface, and the prior choice for the equation of state of dense matter. We find that the radius of a 1.4 solar mass neutron star is most likely from 10 to 14 km and that tighter constraints are only possible with stronger assumptions about the nature of the neutron stars, the systematics of the observations, or the nature of dense matter. Strong phase transitions are preferred over other models and interpretations of the data with a Bayes factor of 8 or more, and in this case, the radius is likely smaller than 12 km. However, radii larger than 12 km are preferred if the neutron stars have uneven temperature distributions.

    ↳ astro-ph.HEastro-ph.SRnucl-thMNRAS(2018)·163 citations
  7. 10

    Cs diffusion in SiC high-energy grain boundaries

    Hyunseok Ko · Izabela Szlufarska · Dane Morgan

    Cesium (Cs) is a radioactive fission product whose release is of concern for Tristructural-Isotropic (TRISO) fuel particles. In this work, Cs diffusion through high energy grain boundaries (HEGBs) of cubic-SiC is studied using an ab-initio based kinetic Monte Carlo (kMC) model. The HEGB environment was modeled as an amorphous SiC (a-SiC), and Cs defect energies were calculated using density functional theory (DFT). From defect energies, it was suggested that the fastest diffusion mechanism as Cs interstitial in an amorphous SiC. The diffusion of Cs interstitial was simulated using a kMC, based on the site and transition state energies sampled from the DFT. The Cs HEGB diffusion exhibited an Arrhenius type diffusion in the range of 1200-1600{\deg}C. The comparison between HEGB results and the other studies suggests not only that the GB diffusion dominates the bulk diffusion, but also that the HEGB is one of the fastest grain boundary paths for the Cs diffusion. The diffusion coefficients in HEGB are clearly a few orders of magnitude lower than the reported diffusion coefficients from in- and out-of- pile samples, suggesting that other contributions are responsible, such as a radiation enhanced diffusion.

    ↳ cond-mat.mtrl-scinucl-thJ.Appl.Phys.(2017)·0 citations

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