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A tutorial on geant4 hadronic physics (GHAD)

A tutorial on geant4 hadronic physics (GHAD). J.P. Wellisch, CERN/EP. With contributions from. T. Ersmark, G. Folger, V.Ivanchenko, A. Kiryunin, R. Nartello, B. Trieu, M. Verderi, J.P.Wellisch, D. Wright. Program. How to use GHAD? Implications for detector construction.

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A tutorial on geant4 hadronic physics (GHAD)

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  1. A tutorial on geant4 hadronic physics (GHAD) J.P. Wellisch, CERN/EP.

  2. With contributions from • T. Ersmark, • G. Folger, • V.Ivanchenko, • A. Kiryunin, • R. Nartello, • B. Trieu, • M. Verderi, • J.P.Wellisch, • D. Wright.

  3. Program • How to use GHAD? • Implications for detector construction. • A look inside (hadronic) processes, or how to tailor. • What models and options are available? • How good is it really? • Where to find more information.

  4. Part 1 How to use GHAD?

  5. Physics lists – defining the physics • GHAD physics, as all other physics, is used through geant4’s physics lists. • A physics lists is (user) code specifying the complete physics modeling used in your application. • Particle types • Decays • Electromagnetic physics • ... • Hadronic physics • It associates processes with particles.

  6. The approach to physics lists

  7. Geant4 physics lists versus geant3 packages • In geant4, the physics lists serve the same purpose as the “packages” (GHEISHA, FLUKA, GCALOR) in geant3. • Conceptually, the two are identical. • They provide the physics and its modeling to an application. • Each “package” is built of a complete and consistent set of models • Early in geant4, the idea was that each user would (have to) build ‘his’ package.

  8. In the case if hadronic physics, the problem was complexity. • It takes 5 levels of implementation framework in geant4 to implement hadronics. • These, and the models implementing them, are used to assemble the hadronic physics for the simulation engine. • The number of options is quite large. • Each comes with trade-offs in descriptive power and performance. • There are 25 particle species to be tracked, that need complete and consistent physics.

  9. Assume we want to study activation.

  10. Hence the educated guess physics lists. • It simply became clear that writing a good physics list is no trivial, in particular when hadronic physics is involved. • It is nice to be able to exploit the full power in the flexibility and variety of hadronic physics modeling in geant4, but being forced to do so is not what we want. • It is also nice to have the physics transparently in front of you and be able to exploit it in the best possible way, but being forced to understand it all is (very understandably) not what people want, either.

  11. Because of this • We have systematically accumulated experience with various combinations of cross-section and models over the last years. • Today we provide a set of physics lists institutionalizing this knowledge. • Publishing them to the general audience was one of the main milestones of the hadronic working group for 2002.

  12. LCG simulation project. HEP calorimetry. HEP trackers. 'Average' collider detector Low energy dosimetric applicationswith neutrons low energy nucleon penetration shielding linear collider neutron fluxes high energy penetration shielding medical and other life-saving neutron applications low energy dosimetric applications high energy production targets e.g. 400GeV protons on C or Be medium energy production targets e.g. 15-50 GeV p on light targets LHC neutron fluxes Air shower applications (still working on this) low background experiments Use case packages of Physics Lists • http://cmsdoc.cern.ch/~hpw/GHAD/HomePage

  13. To make tailoring easier, and the code more readable, we introduced Builders.

  14. Now, what does this mean ? • You can now • Just pick a physics list from the ‘menu’. • Aggregate your own cocktail from limited complexity of the builders • Use all 5 framework levels with their full power. • A structured reduction in the level of complexity exposed to you.

  15. The WWW pages – a small demo. • There is a ‘physics lists’ topic on the geant4 HyperNews. • We go to: • http://cmsdoc.cern.ch/~hpw/GHAD/HomePage

  16. The recommended procedure: • Start by trying the provided physics lists. • It makes it such that results by different groups can be compared. • You will profit from validation and verification done by others. • Of course you are still encouraged to tailor the physics lists that we provide, and/or build your own where you need. • Please also let us know about your findings. • Plots you may whish to provide can enter WWW for everyone’s benefit. Do not use examples/novice/N04 as example for a hadronic physics list.

  17. The support process –static view

  18. The support process – dynamic view

  19. Part 2 Some implications for detector construction

  20. On Material construction • There are three ways to construct materials in geant4 • From it’s isotopic composition • From it’s elements • As an effective material (Aeff, Zeff)

  21. Effective materials • Hadronics cross-section are not a function of material properties, but a function of nuclear properties. • If you use effective numbers, the element composition cannot be automatically recovered. • The cross-section will be ‘highly approximativ’ at best. • The final states will have wrong properties. • Never use effective A, Z with hadronic physics (There are situations, here you will not be able to avoid it, so we cannot protect against it.)

  22. Proton induced reactions

  23. From elementary composition • This is good enough for most high energy applications.

  24. Proton induced reactions

  25. Isotope wise composition • When detailled simulation of low energy neutrons is important, element info is not sufficient (E<20MeV) to get the cross-section and final states right. • For different isotopes, the neutron nuclear resonances will be at entirely different positions • For different isotopes, the final state channels open can differ drastically. •  You may be tempted to construct your materials from Isotopes in this case

  26. Isotope wise composition • In case the neutron_hp models are used (detailed neutron transport below 20MeV), geant4 recovers the natural isotopic composition, in case materials and mixtures are specified in terms of their constituting elements. • If you have enriched isotopes (like Uranium-238), please use the isotopes directly, to specify your material. • Normally you do not need to use the G4Isotope in your detector construction

  27. Example: Neutrons in Lithium • Neutron inelastic cross-section at 150eV: • Li-7: 0.00 millibarns • Li-6: 12.2 barns ! • Open inelastic channels: • Li-7: none • Li-6: nLita (which makes Li-6 a well known shielding isotope)

  28. Part 3 A look inside (hadronic) processes, or how to tailor.

  29. G4Track G4DynamicParticle G4ParticleDefinition G4ProcessManager Process_2 Process_1 Process_3 What is tracked in GEANT4 ? • Propagated by the tracking, • Snapshot of the particle state and location. • Momentum, pre-assigned decay… • The « particle type »: • G4Electron, • G4PionPlus… • « Hangs » the • physics sensitivity; • The classes involved in the building the « physics list » are: • The G4ParticleDefinition concrete classes; • The G4ProcessManager; • The processes; • The physics • processes;

  30. The process tracking interface. • There are three situations, where <tracking> may want to ask information from <process>: • AtRest: • Decay, e+ annihilation … • AlongStep: • To describe ‘continuous’ interactions, • occuring along the path of the particle, • like ionisation; AlongStep PostStep • PostStep actions: • Most hadronic interactions, …

  31. The process tracking interface. • A process will implement any combination of the three AtRest, AlongStep and PostStep actions: • Eg: decay = AtRest + PostStep • Each action defines two methods: • GetPhysicalInteractionLength(): • Used to limit the step size: • because the process « triggers »an interaction, a decay, geometry boundary, a user’s limit … • DoIt(): • Implements the actual action to be applied on the track; • Typically final state generation.

  32. G4VProcess & G4ProcessManager • In praxi the G4ProcessManager has three vectors of actions: • One for the AtRestmethods of the particle; • One for theAlongStep ones; • And one for thePostStepactions. • It is those vectors the user sets up in the physics list and which are used by the tracking.

  33. A word of caution on processes ordering • Ordering of following processes is critical: • Assuming n processes, the ordering of the AlongGetPhysicalInteractionLength of the last processes should be: [n-2] … [n-1] multiple scattering [n] transportation • Why ? • Processes return a « true path length »; • The multiple scattering « virtually folds up » this true path length into a shorter« geometrical » path length; • Based on this new length, the transportation can geometrically limits the step. • For other processes ordering does not matter. 

  34. A few examples of processes G4Transportation G4Decay G4eIonization G4ionIonization G4MuBremsStrahlung G4SynchrotronRadiation G4OpAbsorption G4HadronElasticProcess G4NeutronInelasticProcess Etc.. These are registered with the process managers by the physics lists and the builders.

  35. Hadronic vs. electromagnetic processes • In EM physics (mostly): • 1 process = 1 model and 1 cross-section. • In hadronic physics (mostly): • 1 process = an assembly and selection of many cross-sections data-sets, models, production codes, model components, sub-assemblies, options. • Default cross-section are provided for each process. • You decide in the physics list, what exactly you use. • Mix, match, assemble.

  36. A sample inelastic process.

  37. Cross section logic: “AddDataSet(…)” fills a FILO stack Reg. sequence “GetCrossSection(…)” uses the first applicable dataset Data set 3 Data set 2 Data set 1 Cross section baseline Energy, particle, material, isotope, anything else

  38. A sketch of model management

  39. Part 4 What models and options are available?

  40. Cross section implementations • Default covers all possible situations for hadron interactions. • Carried forward from geant3.21. • Different kinds of cross-section data sets • Some are parametrizations, • Some are theory, • Some read and use large databases.

  41. Cross section implementations • Low energy neutrons • Data both for cross-sections and final state generation. • G4NDL, based on a number of Evaluated Nuclear Data Libraries • Data in a ENDF/B-VI derived data format. • Uses the Unix file-system • Data come from various revisions of ENDF/B, JENDL, FENDL, CENDL, Brond, Jef, MENDL, MENDL-P, EFF, etc.. • Recently we started to add geant4 native evaluations.

  42. Cross section implementations • Proton and neutron reaction cross-sections (Wellisch-Axen systematics) • 0-20GeV for protons • 14MeV-20GeV for neutrons • Alternative pion cross-sections • 0-1TeV • Data for isotope production • From MENDL-2 AND MENDL-2P, and Wellisch-Axen systematics (name was coined by Los Alamos).

  43. Cross section implementations • Ion reaction cross-sections • Tripathi’s cross-section formula for E/A<1GeV, and A>2. • Wellisch-Axen systematics for E/A<20GeV and A>4 for scattering off Hydrogen.

  44. Cross section implementations • Photo and electro-nuclear cross-sections • For all energies • Gammas • GDR, quasi-deuteron, Delta, Roper, reggeon-pomeron contributions parametrizised • Based on 14 nuclei, tested on many more… • Electrons/Positrons • Use method of equivalent photons, and fold the photo-nuclear cross-section • Added hard scattering

  45. Final state generators • Three categories of modeling approaches • Parametrization driven modeling • Data driven modeling • Theory driven modeling

  46. Parameterisation driven models • Two domains: • high energy inelastic (Aachen, CERN) • low energy inelastic, elastic, fission, capture (TRIUMF, UBC, CERN) • Stopping particles • base line (TRIUMF, CHAOS) • mu- (TRIUMF, FIDUNA) • pi- (INFN, CERN, TRIUMF) • K- (Crystal Barrel, TRIUMF) • anti-protons (JLAB, CERN) • Electromagnetic transitions of the exotic atom prior to capture; effects of atomic binding. (Novosibirsk, ESA)

  47. Data driven models: • Low energy neutron transport (neutron_hp), • Radioactive decay (DERA, ESA) • photon evaporation (INFN) • elastic scattering (TRIUMF, U.Alberta, CERN) • internal conversion (ESA), • etc..

  48. Theory driven models • Ultra-high energy models • Parton transport model (U.Frankfurt, in discussion) • High energy models • ‘Fritjof’ type string model (CERN) • Quark gluon String (CERN) • Pythia(7) interface (Lund, CERN) • Intra-nuclear transport models (or replacements) • Hadronic cascade+pre-equilibrium (HIP, CERN) • Binary and Bertini cascades (HIP, CERN, Novosibirsk, SLAC) • QMD type models (CERN, Inst.Th.Phys. Frankfurt) • Chiral invariant phase-space decay (JLAB, CERN, ITEP) • Partial Mars rewrite (Kyoto, Uvic, in collaboration with FNAL) • De-excitation • Evaporation, fission, multi-fragmentation, fermi-break-up (CMS)

  49. Absorption at rest m, p, K, p-bar, n-bar A not totally correct hadronic model summary (I fore sure left off something, like G4LElastic) CHIPS I CHIPS (gamma) LEP Neutron_hp HEP Evap multifrag FTF string Fermi Binary cascade Phot, ev. QGS string conversion Bertini cascade Rad. Dec. Precompound Fission mars LEpp, np 1 MeV 10 MeV 100 MeV 1 GeV 10 GeV 100 GeV 1 TeV 10 TeV 100 TeV

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