PaperPanorama

Nuclear Theory·nucl-th

Wednesday·December 23, 2015

17 papers8 primary·9 cross-listed

  1. 01

    [Submitted on 22 Dec 2015]

    Exploring the Beam Energy Dependence of Flow-Like Signatures in Small System Au Collisions

    J.D. Orjuela Koop🇺🇸 · R. Belmont🇺🇸 · P. Yin🇺🇸 · J.L. Nagle🇺🇸

    Recent analyses of small collision systems, namely and Pb at the LHC and Au, Au and He+Au at RHIC, have revealed azimuthal momentum anisotropies commonly associated with collective flow in larger systems. Viscous hydrodynamics and parton cascade calculations have proved successful at describing some flow-like observables in these systems. These two classes of calculations also confirm these observables to be directly related to the initial geometry of the created medium. However, the question of whether equilibrium dynamics is the dominant driver of the signal remains open, given the short lifetime of small systems. In this regime, pre-equilibrium dynamics and late stage hadronic interactions are expected to play a significant role. Hence, a beam energy scan of small systems---that amounts to varying the initial temperature and the lifetime of the medium---can provide valuable information to shed light on these issues. In this paper, we present predictions from viscous hydrodynamics (SONIC), partonic (AMPT) and hadronic (UrQMD) cascade calculations for elliptic and triangular anisotropy coefficients in +Au at = 7.7, 20, 39, 62.4 and 200 GeV, corresponding to the expected running at RHIC in 2016. We also present predictions for +Pb at = 5.02 TeV, an interesting system to compare to existing Pb data taken at the LHC.

    Comments:
    Added new figure comparing cumulant and event-plane methods
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1512.06949 [pdf]
    PRC(2016)·27 citations
  2. 02

    [Submitted on 22 Dec 2015]

    Recent developments in heavy-ion fusion reactions around the Coulomb barrier

    K. Hagino · N. Rowley🇫🇷 · J.M. Yao🇯🇵

    The nuclear fusion is a reaction to form a compound nucleus. It plays an important role in several circumstances in nuclear physics as well as in nuclear astrophysics, such as synthesis of superheavy elements and nucleosynthesis in stars. Here we discuss two recent theoretical developments in heavy-ion fusion reactions at energies around the Coulomb barrier. The first topic is a generalization of the Wong formula for fusion cross sections in a single-channel problem. By introducing an energy dependence to the barrier parameters, we show that the generalized formula leads to results practically indistinguishable from a full quantal calculation, even for light symmetric systems such as C+C, for which fusion cross sections show an oscillatory behavior. We then discuss a semi-microscopic modeling of heavy-ion fusion reactions, which combine the coupled-channels approach to the state-of-the-art nuclear structure calculations for low-lying collective motions. We apply this method to subbarrier fusion reactions of Ni+Ni and Ca+Ni systems, and discuss the role of anharmonicity of the low-lying vibrational motions.

    Comments:
    10 pages, 6 figures. A talk given at the 5th International Workshop on Compound-Nuclear Reactions and Related Topics (CNR*15), October 9-23, 2015, Tokyo, Japan
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1512.06954 [pdf]
    EPJ Web Conf.(2016)·0 citations
  3. 03

    [Submitted on 22 Dec 2015]

    The In-Medium Similarity Renormalization Group: A Novel Ab Initio Method for Nuclei

    H. Hergert · S. K. Bogner · T. D. Morris · A. Schwenk · K. Tsukiyama

    We present a comprehensive review of the In-Medium Similarity Renormalization Group (IM-SRG), a novel ab inito method for nuclei. The IM-SRG employs a continuous unitary transformation of the many-body Hamiltonian to decouple the ground state from all excitations, thereby solving the many-body problem. Starting from a pedagogical introduction of the underlying concepts, the IM-SRG flow equations are developed for systems with and without explicit spherical symmetry. We study different IM-SRG generators that achieve the desired decoupling, and how they affect the details of the IM-SRG flow. Based on calculations of closed-shell nuclei, we assess possible truncations for closing the system of flow equations in practical applications, as well as choices of the reference state. We discuss the issue of center-of-mass factorization and demonstrate that the IM-SRG ground-state wave function exhibits an approximate decoupling of intrinsic and center-of-mass degrees of freedom, similar to Coupled Cluster (CC) wave functions. To put the IM-SRG in context with other many-body methods, in particular many-body perturbation theory and non-perturbative approaches like CC, a detailed perturbative analysis of the IM-SRG flow equations is carried out. We conclude with a discussion of ongoing developments, including IM-SRG calculations with three-nucleon forces, the multi-reference IM-SRG for open-shell nuclei, first non-perturbative derivations of shell- model interactions, and the consistent evolution of operators in the IM-SRG. We dedicate this review to the memory of Gerry Brown, one of the pioneers of many-body calculations of nuclei.

    Comments:
    92 pages, 33 figures, to appear in Physics Reports
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1512.06956 [pdf]
    Phys.Rept.(2016)·550 citations
  4. 04

    [Submitted on 22 Dec 2015]

    Calculation of nuclear matter in the presence of strong magnetic field using LOCV technique

    G. H. Bordbar · Z. Rezaei

    In the present work, we are interested in the properties of nuclear matter at zero temperature in the presence of strong magnetic fields using the lowest order constraint variational (LOCV) method employing nuclear potential. Our results indicate that in the absence of a magnetic field, the energy per particle is a symmetric function of the spin polarization parameter. This shows that for the nuclear matter, the spontaneous phase transition to a ferromagnetic state does not occur. However, we have found that for the magnetic fields , the symmetry of energy is broken and the energy has a minimum at a positive value of the spin polarization parameter. We have also found that the effect of magnetic field on the value of energy is more significant at the low densities. Our calculations show that at lower densities, the spin polarization parameter is more sensitive to the magnetic field.

    Comments:
    14 pages, 5 figures Romanian J. Phys. 61 (2016) in press
    Subjects:
    Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
    arXiv:
    1512.06993 [pdf]
    Rom.J.Phys.(2016)·2 citations
  5. 05

    [Submitted on 22 Dec 2015]

    Separable Representation of Energy-Dependent Optical Potentials

    Linda Hlophe · Charlotte Elster

    Background. One important ingredient for many applications of nuclear physics to astrophysics, nuclear energy, and stockpile stewardship are cross sections for reactions of neutrons with rare isotopes. Since direct measurements are often not feasible, indirect methods, e.g. (d,p) reactions, should be used. Those (d,p) reactions may be viewed as three-body reactions and described with Faddeev techniques. Purpose. Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. Optical potentials representing the effective interactions in the neutron (proton) nucleus subsystem are usually non-Hermitian as well as energy-dependent. Potential matrix elements as well as transition matrix elements calculated with them must fulfill the reciprocity theorem. The purpose of this paper is to introduce a separable, energy-dependent representation of complex, energy-dependent optical potentials that fulfill reciprocity exactly. Results. Starting from a separable, energy-independent representation of global optical potentials based on a generalization of the Ernst-Shakin-Thaler (EST) scheme, a further generalization is needed to take into account the energy dependence. Applications to nCa, nPb, and pPb are investigated for energies from 0 to 50~MeV with special emphasis on fulfilling reciprocity. Conclusions. We find that the energy-dependent separable representation of complex, energy-dependent phenomenological optical potentials fulfills reciprocity exactly. In addition, taking into account the explicit energy dependence slightly improves the description of the matrix elements.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1512.07084 [pdf]
    PRC(2016)·7 citations
  6. 06

    [Submitted on 22 Dec 2015]

    Noncongruence of phase transitions in strongly interacting matter

    Matthias Hempel · Veronica Dexheimer · Stefan Schramm · Igor Iosilevskiy

    First-order phase transitions (PTs) with more than one globally conserved charge, so-called noncongruent PTs, have characteristic differences compared to congruent PTs (e.g., dimensionality of phase diagrams and location of critical points and endpoints). Here we discuss the noncongruent features of the QCD PT and compare it with the nuclear liquid-gas (LG) PT, for symmetric and asymmetric matter in heavy-ion collisions and neutron stars. In addition, we have identified a principle difference between the LG and the QCD PT: they have opposite slopes in the pressure-temperature plane.

    Comments:
    7 pages, 2 figures, Proceeding of the 14th Marcel Grossmann Meeting 2015
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1512.07116 [pdf]
    4 citations
  7. 07

    [Submitted on 22 Dec 2015]

    The unreasonable effectiveness of hydrodynamics in heavy ion collisions

    Jacquelyn Noronha-Hostler🇺🇸 · Jorge Noronha🇧🇷 · Miklos Gyulassy🇺🇸

    Event-by-event hydrodynamic simulations of AA and pA collisions involve initial energy densities with large spatial gradients. This is associated with the presence of large Knudsen numbers () at early times, which may lead one to question the validity of the hydrodynamic approach in these rapidly evolving, largely inhomogeneous systems. A new procedure to smooth out the initial energy densities is employed to show that the initial spatial eccentricities, , are remarkably robust with respect to variations in the underlying scale of initial energy density spatial gradients, . For TeV LHC initial conditions generated by the MCKLN code, (across centralities) remains nearly constant if the fluctuation scale varies by an order of magnitude, i.e., when varies from 0.1 to 1 fm. Given that the local Knudsen number , the robustness of the initial eccentricities with respect to changes in the fluctuation scale suggests that the vn's cannot be used to distinguish between events with large from events where is in the hydrodynamic regime. We use the 2+1 Lagrangian hydrodynamic code v-USPhydro to show that this is indeed the case: anisotropic flow coefficients computed within event-by-event viscous hydrodynamics are only sensitive to long wavelength scales of order fm and are incredibly robust with respect to variations in the initial local Knudsen number. This robustness can be used to justify the somewhat unreasonable effectiveness of the nearly perfect fluid paradigm in heavy ion collisions.

    Comments:
    Proceedings of the 25th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2015), Kobe, Japan,4 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1512.07135 [pdf]
    NPA(2016)·18 citations
  8. 08

    [Submitted on 22 Dec 2015]

    Long wavelength perfect fluidity from short distance jet transport in quark-gluon plasmas

    Jiechen Xu🇺🇸 · Jinfeng Liao🇺🇸 · Miklos Gyulassy🇺🇸

    We build a new phenomenological framework that bridges the long wavelength bulk viscous transport properties of the strongly-coupled quark-gluon plasma (sQGP) and short distance hard jet transport properties in the QGP. The full nonperturbative chromo-electric (E) and chromo-magnetic (M) structure of the near "perfect fluid" like sQGP in the critical transition region are integrated into a semi-Quark-Gluon-Monopole Plasma (sQGMP) model lattice-compatibly and implemented into the new CUJET3.0 jet quenching framework. All observables computed from CUJET3.0 are found to be consistent with available data at RHIC and LHC simultaneously. A quantitative connection between the shear viscosity and jet transport parameter is rigorously established within this framework. We deduce the MeV dependence of the QGP's : its near vanishing value in the near regime is determined by the composition of E and M charges, it increases as rises, and its high limit is fixed by color screening scales.

    Comments:
    4 pages excluding references, 3 figures, elsarticle style; contributed talk by Jiechen Xu at Quark Matter 2015, Kobe
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1512.07137 [pdf]
    NPA(2016)·0 citations
  9. 09

    [Submitted on 12 Dec 2015] (cross-list from hep-ph)

    Gluonic Structure of the Constituent Quark

    Nikolai Kochelev🇷🇺 · Hee-Jung Lee🇰🇷 · Baiyang Zhang🇨🇳 · Pengming Zhang🇨🇳

    Based on both the constituent quark picture and the instanton model for QCD vacuum, we calculate the unpolarized and polarized gluon distributions in the constituent quark and in the nucleon. Our approach consists of the two main steps. At the first step, we calculate the gluon distributions inside the constituent quark generated by the perturbative quark-gluon interaction, the non-perturbative quark-gluon interaction, and the non-perturbative quark-gluon-pion anomalous chromomagnetic interaction. The non-perturbative interactions are related to the existence of the instantons, strong topological fluctuations of gluon fields, in the QCD vacuum. At the second step, the convolution model is applied to derive the gluon distributions in the nucleon. A very important role of the pion field in producing the unpolarized and the polarized gluon distributions in the hadrons is discovered. We discuss a possible solution of the proton spin problem.

    Comments:
    6 pages, 5 figures, references added, discussion extended
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1512.03863 [pdf]
    PLB(2016)·11 citations
  10. 10

    [Submitted on 18 Dec 2015] (cross-list from hep-ph)

    Multipole decomposition of the nucleon transverse phase space

    C. Lorcé (Ecole Polytechnique, CPHT)🇫🇷 · B. Pasquini (Pavia U. & INFN, Pavia)🇮🇹

    We present a complete study of the leading-twist quark Wigner distributions in the nucleon, discussing both the -even and -odd sector, along with all the possible configurations of the quark and nucleon polarizations. We identify the basic multipole structures associated with each distribution in the transverse phase space, providing a transparent interpretation of the spin-spin and spin-orbit correlations of quarks and nucleon encoded in these functions. Projecting the multipole parametrization of the Wigner functions onto the transverse-position and the transverse-momentum spaces, we find a natural link with the corresponding multipole parametrizations for the generalized parton distributions and transverse-momentum dependent parton distributions, respectively. Finally, we show results for all the distributions in the transverse phase space, introducing a representation that allows one to visualize simultaneously the multipole structures in both the transverse-position and transverse-momentum spaces.

    Comments:
    22 pages, 12 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1512.06744 [pdf]
    PRD(2016)·41 citations
  11. 11

    [Submitted on 21 Dec 2015] (cross-list from hep-ph)

    Jet fragmentation functions in proton-proton collisions using soft-collinear effective theory

    Yang-Ting Chien🇺🇸 · Zhong-Bo Kang🇺🇸 · Felix Ringer🇺🇸 · Ivan Vitev🇺🇸 · Hongxi Xing🇺🇸

    The jet fragmentation function describes the longitudinal momentum distribution of hadrons inside a reconstructed jet. We study the jet fragmentation function in proton-proton collisions in the framework of soft-collinear effective theory (SCET). We find that, up to power corrections, the jet fragmentation function can be expressed as the ratio of the fragmenting jet function and the unmeasured jet function. Using renormalization group techniques, we are able to resum large logarithms of jet radii R in the perturbative expansion of the cross section. We use our theoretical formalism to describe the jet fragmentation functions for light hadron and heavy meson production measured at the Large Hadron Collider (LHC). Our calculations agree very well with the experimental data for the light hadron production. On the other hand, although our calculations for the heavy meson production inside jets are consistent with the PYTHIA simulation, they fail to describe the LHC data. We find that the jet fragmentation function for heavy meson production is very sensitive to the gluon-to-heavy-meson fragmentation function.

    Comments:
    26 pages, 7 figures, published version at JHEP
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1512.06851 [pdf]
    JHEP(2016)·75 citations
  12. 12

    [Submitted on 21 Dec 2015] (cross-list from nucl-ex)

    Precise measurement of alpha_K and alpha_T for the 150.8-keV E3 transition in 111Cd: Test of internal-conversion theory

    N. Nica · J.C. Hardy · V.E. Iacob · T.A. Werke · C.M. Folden III · L. Pineda · M.B. Trzhaskovskaya

    We have measured the K-shell and total internal conversion coefficients, alpha_K and alpha_T, for the 150.8-keV E3 transition in 111Cd to be 1.449(18) and 2.217(26) respectively. The alpha_K result agrees well with Dirac-Fock calculations in which the effect of the K-shell atomic vacancy is accounted for; it extends our precision tests of alpha_K calculations to Z = 48, the lowest Z yet measured. However, the result for alpha_T disagrees by about two standard deviations from the calculated alpha_T value, whether or not the atomic vacancy is included.

    Comments:
    7 pages, two figures. arXiv admin note: text overlap with arXiv:1312.3883
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1512.06898 [pdf]
    PRC(2016)·8 citations
  13. 13

    [Submitted on 21 Dec 2015] (cross-list from hep-ph)

    The quark susceptibility in a generalized dynamical quasiparticle model

    Hamza Berrehrah🇩🇪 · Wolfgang Cassing🇩🇪 · Elena Bratkovskaya🇩🇪 · Thorsten Steinert🇩🇪

    The quark susceptibility at zero and finite quark chemical potential provides a critical benchmark to determine the quark-gluon-plasma (QGP) degrees of freedom in relation to the results from lattice QCD (lQCD) in addition to the equation of state and transport coefficients. Here we extend the familiar dynamical-quasiparticle model (DQPM) to partonic propagators that explicitly depend on the three-momentum with respect to the partonic medium at rest in order to match perturbative QCD (pQCD) at high momenta. Within the extended dynamical-quasi-particle model (DQPM) we reproduce simultaneously the lQCD results for the quark number density and susceptibility and the QGP pressure at zero and finite (but small) chemical potential . The shear viscosity and the electric conductivity from the extended quasiparticle model (DQPM) also turn out in close agreement with lattice results for =0. The DQPM, furthermore, allows to evaluate the momentum , temperature and chemical potential dependencies of the partonic degrees of freedom also for larger which are mandatory for transport studies of heavy-ion collisions in the regime 5 GeV 10 GeV.

    Comments:
    12 pages, 11 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1512.06909 [pdf]
    PRC(2016)·28 citations
  14. 14

    [Submitted on 22 Dec 2015] (cross-list from nucl-ex)

    Statistical model analysis of hadron yields in proton-nucleus and heavy-ion collisions at SIS 18 energies

    G. Agakishiev🇷🇺 · O. Arnold🇩🇪 · A. Balanda🇵🇱 · D. Belver🇪🇸 · A. Belyaev🇷🇺 · J. C. Berger-Chen🇩🇪 · A. Blanco🇵🇹 · M. Böhmer🇩🇪 · J. L. Boyard🇫🇷 · P. Cabanelas🇪🇸 · E. Castro🇪🇸 · S. Chernenko🇷🇺 and 98 other authors

    The HADES data from p+Nb collisions at center of mass energy of = 3.2 GeV are analyzed by employing a statistical model. Accounting for the identified hadrons , , , , allows a surprisingly good description of their abundances with parameters MeV and MeV, which fits well in the chemical freeze-out systematics found in heavy-ion collisions. In supplement we reanalyze our previous HADES data from Ar+KCl collisions at = 2.6 GeV with an updated version of the statistical model. We address equilibration in heavy-ion collisions by testing two aspects: the description of yields and the regularity of freeze-out parameters from a statistical model fit. Special emphasis is put on feed-down contributions from higher-lying resonance states which have been proposed to explain the experimentally observed excess present in both data samples.

    Subjects:
    Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
    arXiv:
    1512.07070 [pdf]
    EPJA(2016)·73 citations
  15. 15

    [Submitted on 22 Dec 2015] (cross-list from hep-ph)

    Sudakov Resummations in Mueller-Navelet Dijet Production

    A. H. Mueller🇺🇸 · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷 · Bo-Wen Xiao🇨🇳 · Feng Yuan🇺🇸

    In high energy hadron-hadron collisions, dijet production with large rapidity separation proposed by Mueller and Navelet, is one of the most interesting processes which can help us to directly access the well-known Balitsky-Fadin-Kuraev-Lipatov evolution dynamics. The objective of this work is to study the Sudakov resummation of Mueller-Navelet jets. Through the one-loop calculation, Sudakov type logarithms are obtained for this process when the produced dijets are almost back-to-back. These results could play an important role in the phenomenological study of dijet correlations with large rapidity separation at the LHC.

    Comments:
    20 pages, 5 figures; v2, refs added
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1512.07127 [pdf]
    JHEP(2016)·55 citations
  16. 16

    [Submitted on 22 Dec 2015] (cross-list from hep-ph)

    Initial state azimuthal anisotropies in small collision systems

    T. Lappi🇫🇮

    Strong multiparticle azimuthal correlations have recently been observed in high energy proton-nucleus collisions. While final state collective effects can be responsible for many of the observations, the domain structure in the classical color field of a high energy nucleus also naturally leads to such correlations. We describe recent calculations of the momentum space 2-particle cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. We find significant differences between Wilson lines from the MV model and from JIMWLK evolution. We also discuss the relation of this calculation to earlier work on the ridge correlation obtained in the "glasma graph" approximation, and to the "color electric field domain model."

    Comments:
    4 pages, 1 figure. Talk at the Quark Matter 2015 conference, September 27 - October 3, 2015, Kobe, Japan
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1512.07209 [pdf]
    NPA(2016)·3 citations
  17. 17

    [Submitted on 22 Dec 2015] (cross-list from hep-lat)

    Charge transport and vector meson dissociation across the thermal phase transition in lattice QCD with two light quark flavors

    Bastian B. Brandt🇩🇪 · Anthony Francis🇨🇦 · Benjamin Jaeger🇬🇧 · Harvey B. Meyer🇩🇪

    We compute and analyze correlation functions in the isovector vector channel at vanishing spatial momentum across the deconfinement phase transition in lattice QCD. The simulations are carried out at temperatures and with MeV for two flavors of Wilson-Clover fermions with a zero-temperature pion mass of MeV. Exploiting exact sum rules and applying a phenomenologically motivated ansatz allows us to determine the spectral function via a fit to the lattice correlation function data. From these results we estimate the electrical conductivity across the deconfinement phase transition via a Kubo formula and find evidence for the dissociation of the meson by resolving its spectral weight at the available temperatures. We also apply the Backus-Gilbert method as a model-independent approach to this problem. At any given frequency, it yields a local weighted average of the true spectral function. We use this method to compare kinetic theory predictions and previously published phenomenological spectral functions to our lattice study.

    Comments:
    28 pages, 6 figures
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1512.07249 [pdf]
    PRD(2016)·94 citations

Affiliations

first authorsco-authorsvia INSPIRE