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Comparison of heavy-ion transport simulations: Collision integral with pions and Δ resonances in a box

Journal Article · · Physical Review. C
 [1];  [2];  [3];  [4];  [5];  [4];  [6];  [7];  [8];  [9];  [10];  [11];  [12];  [13];  [14];  [15];  [16];  [17];  [18];  [19] more »;  [20];  [21];  [22];  [20] « less
  1. Tohoku Univ., Sendai (Japan)
  2. Chinese Academy of Sciences (CAS), Beijing (China)
  3. Istituto Nazionale di Fisica Nucleare (INFN) - Lab. Nazionali del Sud, Catania (Italy)
  4. Michigan State Univ., East Lansing, MI (United States). Dept. of Physics and Astronomy
  5. Texas A & M Univ., College Station, TX (United States)
  6. Huzhou Univ., Huzhou (China)
  7. Univ. of Munich, Garching (Germany)
  8. China Inst. of Atomic Energy, Beijing (China); Guangxi Key Lab. Breeding Base of Nuclear Physics and Technology, Guilin (China)
  9. Shanghai Jiao Tong Univ. (China)
  10. Horia Hulubei National Inst. of Physics and Nuclear Engineering (Romania)
  11. GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt (Germany); Goethe Univ., Frankfurt (Germany)
  12. South China Univ. of Technology, Guangzhou (China)
  13. Tottori Univ., Tottori (Japan); RIKEN Nishina Center (Japan)
  14. Texas A & M Univ., Commerce, TX (United States)
  15. Variable Energy Cyclotron Centre, Kolkata (India)
  16. Akita International Univ. (Japan)
  17. Japan Atomic Energy Agency, Ibaraki (Japan). Research Group for Radiation Transport Analysis
  18. Kyoto Univ. (Japan)
  19. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  20. Sun Yat-Sen Univ., Guangzhou (China)
  21. GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt (Germany)
  22. Beijing Normal Univ., Beijing (China); Beijing Radiation Center (China)
+ Show Author Affiliations
Simulations by transport codes are indispensable for extracting valuable physical information from heavy-ion collisions. Pion observables such as the π-/π+ yield ratio are expected to be sensitive to the symmetry energy at high densities. To evaluate, understand, and reduce the uncertainties in transport-code results originating from different approximations in handling the production of Δ resonances and pions. We compare ten transport codes under controlled conditions for a system confined in a box, with periodic boundary conditions, and initialized with nucleons at saturation density and at a temperature of 60 MeV. The reactions NN↔NΔ and Δ↔Nπ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Thus, these are cascade calculations including pions and Δ resonances. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. For the numbers of Δ and π, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of reactions, such as collisions and decays, that take place in the same time step. Better agreements with the reference values are seen in the reaction rates and the number ratios among the isospin species of Δ and π. Both the reaction rates and the number ratios are, however, affected by the correlations between particle positions, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in many of the transport calculations. The uncertainty in the transport-code predictions of the π-/π+ ratio, after letting the existing Δ resonances decay, is found to be within a few percent for the system initialized at n/p=1.5. In conclusion, the uncertainty in the final π-/π+ ratio in this simplified case of particles in a box is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved in future applications. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Michigan State Univ., East Lansing, MI (United States); Texas A & M Univ., College Station, TX (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Grant/Contract Number:
AC02-05CH11231; SC0013702; SC0019209
OSTI ID:
1582341
Alternate ID(s):
OSTI ID: 1658240
OSTI ID: 1596129
Journal Information:
Physical Review. C, Journal Name: Physical Review. C Journal Issue: 4 Vol. 100; ISSN PRVCAN; ISSN 2469-9985
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

Probing the Symmetry Energy with the Spectral Pion Ratio text January 2021
Sensitivity of the excitation functions of collective flow to relativistic scalar and vector meson interactions in the relativistic quantum molecular dynamics model RQMD.RMF journal November 2019

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73 NUCLEAR PHYSICS AND RADIATION PHYSICS
Low & intermediate energy heavy-ion reactions
Models & methods for nuclear reactions
Molecular dynamics
Particle & resonance production
Symmetry energy
Test-particle methods
heavy ion collisions
transport theory
code comparison
pion production