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Nuclear Theory·nucl-th

Friday·May 1, 2020

13 papers—7 primary·6 cross-listed

All13Primary7Cross-lists6
  1. 01

    Classification of Equation of State in Relativistic Heavy-Ion Collisions Using Deep Learning

    Yu. Kvasiuk🇳🇴 · E. Zabrodin🇳🇴 · L. Bravina🇳🇴 · I. Didur🇺🇦 · M. Frolov🇺🇦

    Convolutional Neural Nets, which is a powerful method of Deep Learning, is applied to classify equation of state of heavy-ion collision event generated within the UrQMD model. Event-by-event transverse momentum and azimuthal angle distributions of protons are used to train a classifier. An overall accuracy of classification of 98\% is reached for Au+Au events at GeV. Performance of classifiers, trained on events at different colliding energies, is investigated. Obtained results indicate extensive possibilities of application of Deep Learning methods to other problems in physics of heavy-ion collisions.

    nucl-thcs.LGhep-phnucl-exJHEP(2020)·12 citations
  2. 02

    Constraining the quadrupole deformation of atomic nuclei with relativistic nuclear collisions

    Giuliano Giacalone🇫🇷

    Preliminary data by the STAR collaboration at the BNL Relativistic Heavy Ion Collider shows that the elliptic flow, , and the average transverse momentum, , of final-state hadrons produced in high-multiplicity U+U collisions are negatively correlated. This observation brings experimental evidence of a significant prolate deformation, , in the colliding U nuclei. I show that a quantitative description of this new phenomenon can be achieved within the hydrodynamic framework of heavy-ion collisions, and that thus such kind of data in the context of high-energy nuclear experiments can help constrain the quadrupole deformation of the colliding species.

    nucl-thhep-exhep-phnucl-exPRC(2020)·71 citations
  3. 03

    Moravcsik's theorem on complete sets of polarization observables reexamined

    Y. Wunderlich🇩🇪 · P. Kroenert🇩🇪 · F. Afzal🇩🇪 · A. Thiel🇩🇪

    We revisit Moravcsik's theorem on the unique extraction of amplitudes from polarization observables, which has been originally published in 1985. The proof is (re-) written in a more formal and detailed way and the theorem is corrected for the special case of an odd number of amplitudes (this case was treated incorrectly in the original publication). Moravcsik's theorem, in the modified form, can be applied in principle to the extraction of an arbitrary number of helicity amplitudes. The uniqueness theorem is then applied to hadronic reactions involving particles with spin. The most basic example is Pion-Nucleon scattering (), the first non-trivial example is pseudoscalar meson photoproduction () and the most technically involved case treated here is given by pseudoscalar meson electroproduction (). The application of Moravcsik's theorem to electroproduction yields new results, which for the first time provide insights into the structure and content of complete sets for this particular process. The uniqueness-statements for the various reactions are compared and an attempt is made to recognize general patterns, which emerge under the application of the theorem.

    nucl-thPRC(2020)·11 citations
  4. 04

    Microscopic calculation of proton and alpha-particle inelastic scattering to study the excited states of He and He

    Yoshiko Kanada-En'yo · Kazuyuki Ogata

    Elastic and inelastic cross sections of the , , and reactions were investigated using the Melbourne -matrix folding approach with the theoretical densities of and obtained by a microscopic structure model of antisymmetrized molecular dynamics (AMD). Microscopic coupled-channel (MCC) calculations of the and reactions were performed to investigate transition properties of the and states. The MCC+AMD calculations reproduced elastic cross sections of the reaction at MeV/A and of the reaction at and 72 MeV/A, which have both been measured by inverse kinematics experiments. For inelastic scattering to the state, the calculated result was in reasonable agreement with the data at and 40.9 MeV/A and supported the AMD prediction of the neutron transition matrix element fm. For the inelastic scattering to , the MCC+AMD calculation overshot the cross sections at MeV/A by a factor of three. According to a phenomenological model analysis, values in the range of 4--6 fm were favored to reproduce the cross sections of the reaction at MeV/A. For the reaction, the MCC+AMD calculation reproduced the elastic cross sections at MeV/A. Theoretical predictions of the () and () cross sections to the , , and states are also given.

    nucl-th2 citations
  5. 05

    Determining distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to Be

    A.M. Moro · J.A. Lay · J.Gómez-Camacho

    A novel method to extract the strength of a weakly bound nucleus from experimental Coulomb dissociation data is proposed. The method makes use of continuum discretized coupled channels (CDCC) calculations, in which both nuclear and Coulomb forces are taken into account to all orders. This is a crucial advantage with respect to the standard procedure based on the Equivalent Photon Method (EPM) which does not properly take into account nuclear distortion, higher order coupling effects, or Coulomb-nuclear interference terms. The procedure is applied to the Be nucleus using two sets of available experimental data at different energies, for which seemingly incompatible have been reported using the EPM. We show that the present procedure gives consistent strengths, thus solving the aforementioned long-standing discrepancy between the two measurements.

    nucl-thnucl-exPLB(2020)·18 citations
  6. 06

    He and Li cluster structures in light nuclei

    Naoyuki Itagaki · Tokuro Fukui · Junki Tanaka · Yuma Kikuchi

    The possibility of the He and Li clusters in atomic nuclei is discussed. Until now most of the clusters in the conventional models have been limited to the closures of the three-dimensional harmonic oscillators, such as He, O, and Ca. In the neutron-rich nuclei, however, the neutron to proton ratio is not unity, and it is worthwhile to think about more neutron-rich objects with as the building blocks of cluster structures. Here the nuclei with the neutron number six, which is the subclosure of the subshell of the -coupling shell model, are assumed to be clusters, and thus we study the He and Li cluster structures in Be (He+He), B (He+Li), C (Li+Li), and C (He+He+He). Recent progress of the antisymmetrized quasi cluster model (AQCM) enables us to utilize -coupling shell model wave functions as the clusters rather easily. It is shown that the He+Li and Li+Li cluster configurations cover the lowest shell-model states of B and C, respectively. To predict the cluster states with large relative distances, we increase the expectation value of the principal quantum numbers by adding the nodes to the lowest states under the condition that the total angular momentum is unchanged (equal to ). As a result, developed cluster states are obtained around the corresponding threshold energies. The rotational band structure of C, which reflect the symmetry of equilateral triangular configuration ( symmetry) of three He clusters, also appears around the threshold energy.

    nucl-thPRC(2020)·12 citations
  7. 07

    Quantifying alpha clustering in light nuclei from binding energies

    K. Fossez

    What is the origin of nuclear clustering and how does it emerge from the nuclear interaction? While there is ample experimental evidence for this phenomenon, its theoretical characterization directly from nucleons as degrees of freedom remains a challenge, making it difficult to improve nuclear forces using clustering observables. In this work, a simple ratio of energies based on effective scale arguments is proposed to assess the quality of nuclear forces on alpha clustering () in bound and narrow ground-state nuclei. The proposed clustering ratio is parameter-free and correctly identify basic alpha clustering features in light nuclei. It is found that in nuclei ranging from to , state-of-the-art \textit{ab initio} nuclear forces underestimate the degree of alpha clustering in key nuclei such as and . Stringent constraints on binding energies are then provided by back-propagating 10\% relative uncertainties on the experimental clustering ratios using a parallel Markov chain Monte Carlo algorithm. It is demonstrated that the binding energies of the nuclei Li, Be, B, and C need to be obtained within tens of keV precision by nuclear forces to ensure a proper reproduction of basic alpha clustering features in light nuclei. This study provides a new and practical path to guide future optimizations of nuclear forces with a potential impact for medium-mass nuclei.

    nucl-thnucl-ex1 citation

Affiliations

first authorsco-authorsvia INSPIRE