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Nuclear Theory·nucl-th

Monday·August 5, 2019

5 papers—4 primary·1 cross-listed

All5Primary4Cross-lists1
  1. 01

    [Submitted on 2 Aug 2019]

    Toward a reliable description of reactions in the distorted-wave impulse approximation

    Nguyen Tri Toan Phuc · Kazuki Yoshida · Kazuyuki Ogata

    Background: Proton-induced nucleon knockout reactions have been successfully used to study the single-particle nature of stable nuclei in normal kinematics with the distorted-wave impulse approximation (DWIA) framework. Recently, these reactions have been applied to rare-isotope beams at intermediate energies in inverse kinematics to study the quenching of spectroscopic factors. Purpose: Our goal is to investigate the effects of various corrections and uncertainties within the standard DWIA formalism on the cross sections. The consistency of the extracted reduction factors between DWIA and other methods is also evaluated. Method: We analyze the and reactions data measured at the RB/LAND setup at GSI for carbon, nitrogen, and oxygen isotopes in the incident energy range of 300--450 MeV/u. Cross sections and reduction factors are calculated by using the DWIA method. The transverse momentum distribution of the C(,)B reaction is also investigated. Results: We have found that including the nonlocality corrections and the Møller factor affects the cross sections considerably. The proton-neutron asymmetry dependence of reduction factors extracted by the DWIA calculation is very weak and consistent with those given by other reaction methods and \textit{ab initio} structure calculations. Conclusions: The results found in this work provide a detailed investigation of the DWIA method for reactions at intermediate energies. They also suggest that some higher-order effects, which is essential for an accurate cross-section description at large recoil momentum, is missing in the current DWIA and other reaction models.

    Comments:
    8 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1908.00667 [pdf]
    PRC(2019)·19 citations
  2. 02

    [Submitted on 2 Aug 2019]

    Normal-ordered -body approximation in particle-number-breaking theories

    Julien Ripoche🇫🇷 · Alexander Tichai🇫🇷 · Thomas Duguet🇫🇷

    The reach of ab initio many-body theories is rapidly extending over the nuclear chart. However, dealing fully with three-nucleon, possibly four-nucleon, interactions makes the solving of the A-body Schrödinger equation particularly cumbersome, if not impossible beyond a certain nuclear mass. Consequently, ab initio calculations of mid-mass nuclei are typically performed on the basis of the normal-ordered two-body (NO2B) approximation that captures dominant effects of three-nucleon forces while effectively working with two-nucleon operators. A powerful idea currently employed to extend ab initio calculations to open-shell nuclei consists of expanding the exact solution of the A-body Schrödinger equation while authorizing the approximate solution to break symmetries of the Hamiltonian. In this context, operators are normal ordered with respect to a symmetry-breaking reference state such that proceeding to a naive truncation may lead to symmetry-breaking approximate operators. The purpose of the present work is to design a normal-ordering approximation of operators that is consistent with the symmetries of the Hamiltonian while working in the context of symmetry broken (and potentially restored) methods. Focusing on many-body formalisms in which U(1) global-gauge symmetry associated with particle number conservation is broken (and potentially restored), a particle-number-conserving normal-ordered k-body (PNOkB) approximation of an arbitrary N-body operator is designed on the basis of Bogoliubov reference states. A numerical test based on particle-number projected Hartree-Fock-Bogoliubov calculations permits to check the particle-number conserving/violating character of a given approximation to a particle-number conserving operator. Using the presently proposed PNOkB approximation, ab initio calculations based on symmetry-breaking and restored formalisms can be safely performed.

    Comments:
    27 pages, 12 figures, 6 tables, submitted to EPJA
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1908.00765 [pdf]
    EPJA(2020)·24 citations
  3. 03

    [Submitted on 2 Aug 2019]

    Jet overlap in heavy ion collisions at LHC energies and its consequences on jet shape

    Iurii Karpenko🇫🇷 · Joerg Aichelin🇫🇷 · Pol Gossiaux🇫🇷 · Martin Rohrmoser🇵🇱 · Klaus Werner🇫🇷

    Central lead-lead collisions at the LHC energies may pose a particular challenge for jet identification as multiple jets are produced per each collision event. We simulate the jet evolution in central Pb-Pb events at GeV collision energy with EPOS3 initial state, which typically contains multiple hard scatterings in each event. Therefore the partons from different jets have a significant chance to overlap in momentum space. We find that 30% of the jets with GeV, identified by the standard anti- jet finding algorithm with jet cone size R=0.3, contain `intruder' particles from overlapping generator-level jets. This fraction increases with increasing beam energy and increasing R. The reconstructed momentum of the jet differs from that of the modelled jet by the loss due to jet partons which are outside of the jet cone and by the gain due to intruder partons. The sum of both may be positive or negative. These intruder partons particularly affect the radial jet momentum distribution because they contribute mostly at large angles with respect to the jet centre. The study stresses the importance of the jet overlap effect emerging in central lead-lead collisions at the LHC energies, while being negligible in peripheral PbPb or Pb/ collisions.

    Comments:
    7 pages, 10 figures; version accepted for Physical Review C
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1908.00836 [pdf]
    PRC(2020)·0 citations
  4. 04

    [Submitted on 2 Aug 2019]

    Nuclear Theory and Event Generators for Charge-Changing Neutrino Reactions

    J. W. Van Orden🇺🇸 · T. W. Donnelly🇺🇸

    Semi-inclusive cross sections based on factorized cross sections are studied for a selection of spectral function models with the objective of facilitating the choice of models for use as input into event generators. The basic formalism for such cross sections is presented along with an introduction to constructing spectral functions for simple models based on the independent particle shell model (IPSM), the relativistic Fermi gas model (RFG) and a local density approximation (LDA) based on the RFG. Spectral functions for these models are shown for O along with a more sophisticated model which includes nucleon-nucleon interactions \cite{ALVAREZRUSO20181}. Inclusive and semi-inclusive cross sections are calculated for these models. Although the inclusive cross sections are all of similar size and shape, the semi-inclusive cross sections are subtantially different depending upon whether the spectral functions contain some features associated with the nuclear shell model or are based on the RFG and LDA models. Calculations of average values and standard deviations of the initial neutrino energy using the semi-inclusive cross section for the various models are presented and indicate that there may be simple kinematical descriptions of the average neutrino energy which is common to all of these models.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1908.00932 [pdf]
    PRC(2019)·29 citations
  5. 05

    [Submitted on 1 Aug 2019] (cross-list from hep-ph)

    Chiral kinetic theory from the on-shell effective theory: derivation of collision terms

    Stefano Carignano🇪🇸 · Cristina Manuel🇪🇸 · Juan M. Torres-Rincon🇩🇪

    We show that the on-shell effective theory (OSEFT) is the quantum field theory counterpart of a Foldy-Wouthuysen diagonalization of relativistic quantum mechanics for massless fermions. Thus, it is free of the Zitterbewegung oscillations that would yield an ill-defined meaning to the semiclassical transport approach at short distances if derived from the pure Dirac picture. We present a detailed derivation of the collision terms in the chiral kinetic theory using the OSEFT. Collision integrals are derived up to order 1/E, where E is the energy of an on-shell fermion. At this order, the collision terms depends on the spin tensor of the fermion, and in the presence of chiral imbalance, it describes how a massless fermion of a given helicity interacts differently with the transverse photons of different circular polarization. In order to back up our results, we check that they allow us to reproduce the fermion decay rate in an ultradegenerate plasma with a chiral imbalance computed directly from QED.

    Comments:
    36 pages, 2 figures, title and abstract modified, version largely extended with more details and discussions, results and conclusions unchanged
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    1908.00561 [pdf]
    PRD(2020)·37 citations

Affiliations

first authorsco-authorsvia INSPIRE