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Nuclear Theory·nucl-th

Thursday·April 25, 2024

8 papers—6 primary·2 cross-listed

All8Primary6Cross-lists2
  1. 07

    [Submitted on 24 Apr 2024] (cross-list from nucl-ex)

    Electric and magnetic dipole strength in Ni from forward-angle inelastic proton scattering

    I. Brandherm (1) · P. von Neumann-Cosel (1) · R. Mancino (1,2,3) · G. Martínez-Pinedo (1,2) H. Matsubara (4,5) · V.Yu. Ponomarev (1) · A. Richter (1) · M. Scheck (6,7) A. Tamii (4) ((1) Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany, (2) GSI Helmholzzentrum für Schwerionenforschung, Planckstraße 1, Darmstadt, Germany, (3), Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic, (4) Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka, Japan, (5) Faculty of Radiological Technology, Fujita Health University, Aichi, Japan, (6) School of Computing, Engineering, and Physical Sciences, University of the West of Scotland, Paisley, United Kingdom, (7) SUPA, Scottish Universities Physics Alliance, United Kingdom)

    The aim of the present work is a state-by-state analysis of possible E1 and M1 transitions in Ni with a high-resolution (p,p') experiment at 295 MeV and very forward angles including 0{\deg} and a comparison to results from studies of the dipole strength with the and (e,e') reactions. The E1 and M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposition analysis and converted to reduced E1 and spin-M1 transition strengths using the virtual photon and the unit cross-section method, respectively. Despite the high level density good agreement is obtained for the deduced excitation energies of J = 1 states in the three types of experiments indicating that the same states are excited. The B(E1) and B(M1) strengths from the experiments are systematically smaller than in the present work because of the lack of information on branching ratios to lower-lying excited states and the competition of particle emission. Fair agreement with the B(M1) strengths extracted from the (e,e') data is obtained after removal of E1 transitions uniquely assigned in the present work, which belong to a low-energy toroidal mode with unusual properties mimicking M1 excitations in electron scattering. The experimental M1 strength distribution is compared to large-scale shell-model calculations with the effective GXPF1A and KB3G interactions. They provide a good description of the isospin splitting and the running sum of the M1 strength. A quenching factor 0.74 for the spin-isospin part of the M1 operator is needed to attain quantitative agreement with the data.

    Comments:
    16 pages, 15 figures
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2404.15906 [pdf]
    PRC(2024)·5 citations
  2. 08

    [Submitted on 24 Apr 2024] (cross-list from hep-ph)

    Symmetries in particle physics: from nuclear isospin to the quark model

    Bruno Berganholi🇧🇷 · Gláuber C. Dorsch🇧🇷 · Beatriz M. D. Sena🇧🇷 · Giovanna F. do Valle🇧🇷

    We present a concise pedagogic introduction to group representation theory motivated by the historical developments surrounding the advent of the Eightfold Way. Abstract definitions of groups and representations are avoided in favour of the physical intuition of symmetries of the nuclear interaction. The concept of nuclear isospin is used as a physical motivation to introduce SU(2) and discuss the main techniques of representation theory. The discovery of strange particles motivates extending the symmetry group to SU(3), at first in the context of the Sakata model. We highlight the successes in fitting mesons in the SU(3) octet, discuss the drawbacks of the Sakata model for baryonic classifications, and how the Eightfold Way finally led to the quark model. This approach has two major advantages: (i) the main concepts of the theory of Lie groups are introduced and discussed without ever losing touch with its applications in particle physics; (ii) it allows the beginner to study group theory while also becoming acquainted with the historical developments of particle physics that led to the concept of quarks. In particular, in this pedagogical path the quarks appear as yet another class of particles predicted from symmetry principles, rather than being introduced ad hoc for postulating an SU(3) symmetry, as usually done in the literature.

    Comments:
    12 figures, 24 pages
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2404.15988 [pdf]
    Eur.J.Phys.(2024)·3 citations

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first authorsco-authorsvia INSPIRE