Updates and Perspectives of Geant4 Hadronic Physics for Space Applications

1. 7th Geant4 Space Users Workshop Dennis Wright 19 August 2010 Updates and Perspectives of Geant4 Hadronic Physics for Space Applications

2. Recent Improvements in Hadronic Models 2

3. High Energy Models • The quark-gluon string (QGS) and Fritiof string Fragmentation (FTF) models deal with interactions from ~10 GeV to ~TeV • past improvements in QGS have improved shower shape descriptions in test beams • recent improvements in FTF have made this model much more competitive with QGS, and increased its range of application • LHC data now coming in will provide stringent tests of these models • for the first time we will be able to test above 1 TeV 3

4. p C -> X at 150 GeV/c (NA49 data)FTFP G4 8.2, FTFP G4 9.3.p01, QGSP G4 9.2 beta 4

5. Transition Region (5-15 GeV) • In many physics lists (e.g. QGSP_BERT) the cascade model transitions to a string model over the range 5 - 15 GeV • in QGSP_BERT: • 0 < BERT < 9.9 GeV • 9.5 < LEP < 15 GeV • 12 < QGSP • narrow transition range and mismatch between models causes a discontinuity • Discontinuity in transition region shows up in several comparisons with data • data from HARP-CDP group is perhaps most dramatic 5

6. p Ta -> + X (200 <  < 500) 6

7. Cascades (1) • Cascade codes deal typically with incident hadrons of KE < 10 GeV • Many improvements in Bertini-style cascade both in physics and CPU performance • see talk by Mike Kelsey • INCL/ABLA is a cascade + de-excitation code which is more data-driven, hence more precise • this model could be a useful alternative to the Binary or Bertini codes for energies below 3 GeV • spallation • fragment production • development now underway to extend model to 5 GeV 7

8. Cascades (2) • Binary cascade is a native Geant code based on a time-dependent intra-nuclear cascade • alternative to Bertini cascade or INCL/ABLA • somewhat lower upper bound in energy than Bertini, higher than INCL/ABLA • performs well in spallation region ( < 3 GeV) • interfaced to G4 precompound model to handle nuclear de-excitation after cascade phase • Binary cascade can be interfaced to string models to do re-scattering of secondaries from the initial interaction • potentially a more physical way to merge one model into another • similar method may be tried in Bertini 8

9. Precompound Model • The precompound model takes over after the cascade or string interactions are complete • takes highly excited residual nucleus down to the equilibrium stage • can be used by itself for incident p and n with KE < 200 MeV • particle emission is governed by probability nucleus is in a given excited state (density of states) X cross section for emitting a particle from that state (inverse absorption cross section) • Recent improvements include: • more careful treatment of density of states formula • new inverse absorption cross sections parameterized with up-to-date data 9

10. De-excitation Models • Various de-excitation models compete with one another to de-excite equilibrium nucleus to ground or low-lying states • evaporation of p, n, d, t, 3He and a particles • gamma emission • statistical multi-fragmentation • fission (for heavy nuclei) and disintegration (for light nuclei) • Recent improvements include: • new hybrid evaporation model: • Weisskopf-Ewing standard evaporation model for light fragments (p, n, t, 3He, a) • Generalized Evaporation Model (GEM) for fragments with A < 29 • tuning and bug-fixes of fission parameters 10

11. Pb + H -> fission at 1GeV/A (before and after improvements to G4 fission code) 11

12. Other Models • G4 QMD model: • a nucleus-nucleus collision model • alternative to Light Ion Binary Cascade model • see talk by Tatsumi Koi • high precision neutrons and possible alternative codes • see talk by Tatsumi Koi • Chiral Invariant Phase Space model • best model we have for electro- and gamma-nuclear • general hadron interaction model originally developed for stopped hadrons • extended to nuclear de-excitation • most recently extended to cascade and string energy ranges, but still being tested there 12

13. Validation Progress and New Efforts 13

14. SATIF 10 • SATIF: a yearly inter-code validation against data taken for shielding applications • typically 5 or 6 other simulation codes are represented • One of the many tests measured neutron attenuation length in concrete and steel • neutrons produced by p + Hg -> n + X at 2.83 GeV and 24 GeV at BNL AGS • neutrons pass into steel or concrete where they activate embedded Bi detectors: (n, 4n) and (n,6n) reactions • Geant4 entered the FTFP_BERT physics list • a little better than QGSP_BERT (see next slide) • high precision neutron cross sections from G4NDL were augmented by JENDL high energy cross sections 14

15. Agreement Level: abs{ ln(sim/data) } for various Geant4 Physics Lists 15

17. IAEA Validation • A yearly inter-code comparison project to study mainly spallation reactions • “new” data supplied to code developers to do comparison • workshop held to discuss differences • typical incident energies range from 25 MeV to 3 GeV • Has been very useful to Geant4 model development • provided access to data we had not seen before • pointed out model deficiencies in regions we had not studied before 17

18. IAEA p + Au -> d + X at 1.2 GeV (Bertini vs. Binary vs. data) 18

19. G4Bic G4Bert Incl/Abla

20. Proposed Hadronic Validation Access Page 20

21. Plans for the Upcoming Year 21

22. Shower Shapes 22

23. Shower Shapes • Even after recent improvements, our physics lists still produce showers which are too short and narrow • past improvements in QGS have improved shower shape descriptions in test beams • recent improvements in FTF have made this model much more competitive with QGS, and increased its range of application • What is needed? • a detailed study of the spectrum of low energy particles produced by the cascade models • a more physical way of merging the cascades into the string models (re-scattering or formation time) 23

24. Transition Region • Eliminate the use of LEP models in physics lists • do not conserve energy • contribute to discontinuity in 9-15 GeV energy range • will still be required for some of the more exotic particles (anti-protons, hyperons, etc.) • To do this we must extend cascade codes upward in energy, string codes down in energy • FTF and Bertini are likely candidates • new physics list required with wider merge region between the models 24

25. Cross Section Re-design • G4 hadronic group recently undertook a review of the hadronic cross sections because: • the number of cross section data sets is increasing • these sets are not currently handled in a consistent way • their use in physics lists is confusing to both users and developers • the merging of two data sets over a given energy range is not always smooth • Preliminary plan • base everything on “cross section components”: fragments of original code or data that may be combined to form cross section data sets, and used interchangeably at the model or process level • new machinery for smooth merging and naming 25

26. Improving CPU Performance • Both speed and memory footprint of most hadronic codes need to be addressed • already significant progress on Bertini cascade • next target: precompound model • Methods • reduce creation and deletion of objects • make better use of look-up tables (e.g. for trig functions, etc.) • use optimized math functions (integer arguments instead of real where possible) • better coding techniques 26