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Geant4 - a simulation toolkit -

Geant4 - a simulation toolkit -. Makoto Asai (SLAC Computing Services) On behalf of the Geant4 Collaboration December 1 st , 2003 ACAT03 @ KEK. Contents. General introduction and brief history Geant4 kernel Geometry Physics Highlights of the new developments

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Geant4 - a simulation toolkit -

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  1. Geant4- a simulation toolkit - Makoto Asai (SLAC Computing Services) On behalf of the Geant4 Collaboration December 1st, 2003 ACAT03 @ KEK

  2. Contents • General introduction and brief history • Geant4 kernel • Geometry • Physics • Highlights of the new developments • Highlights of user applications • User support processes • Summary Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  3. General introduction and brief history

  4. What is Geant4? • Geant4 is an object-oriented toolkit for simulation of elementary particles passing through and interacting with matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. • Geant4's application area includes high energy and nuclear physics experiments, accelerator and shielding studies, space engineering, medical physics and several other fields. • Geant4 is the successor of GEANT3, the world-standard toolkit for HEP detector simulation. Geant4 is one of the first successful attempt to re-design a major package of HEP software for the next generation of experiments using an Object-Oriented environment. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  5. Flexibility of Geant4 • In order to meet wide variety of requirements from various application fields, a large degree of functionality and flexibility are provided. • Geant4 has many types of geometrical descriptions to describe most complicated and realistic geometries • CSG, BREP, Boolean • XML interface • The physics processes offered cover a comprehensive range including electromagnetic, hadronic and optical processes for a large set of long-lived particles in materials and elements, over a wide energy range. The applicable energy range begins, in some cases, from 100 eV and extends up to the TeV energy range. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  6. Physics in Geant4 • It is rather unrealistic to develop a uniform physics model to cover wide variety of particles and/or wide energy range. • Much wider coverage of physics comes from mixture of theory-driven, parameterized, and empirical formulae. Thanks to polymorphism mechanism, both cross-sections and models (final state generation) can be combined in arbitrary manners into one particular process. • Standard EM processes • Low energy EM processes • Hadronic processes • Photon/lepton-hadron processes • Optical photon processes • Decay processes • Shower parameterization • Event biasing technique Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  7. Geant4 – Its history and future • Dec ’94 - Project start • Apr ’97 - First alpha release • Jul ’98 - First beta release • Dec ’98 - Geant4 0.0 (first public) release • Jul ’99 - Geant4 0.1 release • … • Jun ’03 - Geant4 5.2 release • Dec 12th, ’03 - Geant4 6.0 release (planned) • We currently provide two to three public releases and bimonthly beta releases in between public releases every year. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  8. HARP Geant4 Collaboration PPARC Univ. Barcelona Lebedev Collaborators also from non-member institutions, including Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University Helsinki Inst. Ph. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  9. Geant4 kernel

  10. Geant4 kernel • Geant4 consists of 17 categories. • Independently developed and maintained by WG(s) responsible to each category. • Interfaces between categories (e.g. top level design) are maintained by the global architecture WG. • Geant4 Kernel • Handles run, event, track, step, hit, trajectory. • Provides frameworks of geometrical representation and physics processes. Geant4 Inter Visuali Readout faces zation Run Persis tency Event Tracking Digits + Processes Hits Track Geometry Particle Graphic Material _reps Intercoms Global Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  11. Tracking and processes • Geant4 tracking is general. • It is independent to • the particle type • the physics processes involving to a particle • It gives the chance to all processes • To contribute to determining the step length • To contribute any possible changes in physical quantities of the track • To generate secondary particles • To suggest changes in the state of the track • e.g. to suspend, postpone or kill it. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  12. Processes in Geant4 • In Geant4, particle transportation is a process as well, by which a particle interacts with geometrical volume boundaries and field of any kind. • Because of this, for example, shower parameterization process can take over from the ordinary transportation without modifying the transportation process. • Each particle has its own list of applicable processes. At each step, all processes listed are invoked to get proposed physical interaction lengths. • The process which requires the shortest interaction length (in space-time) limits the step. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  13. Cuts in Geant4 • A Cut in Geant4 is a production threshold. • Only for physics processes that have infrared divergence • Not tracking cut, which does not exist in Geant4 • Energy threshold must be determined at which discreteenergy loss is replaced by continuous loss • Old way: • Track primary particle until cut-off energy is reached,calculate continuous loss and dump it at that point,stop tracking primary • Create secondaries only above cut-off energy, or add to continuous loss of primary for less energetic secondaries • Geant4 way: • Specify range (which is converted toenergy for each material) at which continuous loss begins, trackprimary particle one more step to make it down to zero range • Create secondaries only above specified range, or add to continuous loss of primary for less energetic secondaries Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  14. Energy cut vs. range cut • 500 MeV/c proton in liq.Ar (4mm) / Pb (4mm) sampling calorimeter • Geant3 (energy cut) • Ecut = 450 keV liq.Ar Pb liq.Ar Pb • Geant4 (range cut) • Rcut = 1.5 mm • Corresponds to Ecut in liq.Ar = 450 keV, Ecut in Pb = 2 MeV Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  15. Geometry

  16. G4VSolid G4LogicalVolume G4VPhysicalVolume G4Material G4Box G4VisAttributes G4PVPlacement G4VSensitiveDetector G4Tubs G4PVParameterised Volume • Three conceptual layers • G4VSolid -- shape, size • G4LogicalVolume -- daughter physical volumes, material, sensitivity, user limits, etc. • G4VPhysicalVolume -- position, rotation • Hierarchal three layers of geometry description allows maximum reuse of information to minimize the use of memory space. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  17. Solid • Geant4 geometry module supports variety of representations of shapes. • CSG (Constructed Solid Geometry) solids • G4Box, G4Tubs, G4Cons, G4Trd, … • Analogous to simple GEANT3 CSG solids • Specific solids (CSG like) • G4Polycone, G4Polyhedra, G4Hype, … • BREP (Boundary REPresented) solids • G4BREPSolidPolycone, G4BSplineSurface, … • Any order surface • Boolean solids • G4UnionSolid, G4SubtractionSolid, … Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  18. Physical volume • G4PVPlacement 1 Placement = One Volume • A volume instance positioned once in its mother volume • G4PVParameterised 1 Parameterized = Many Volumes • Parameterized by the copy number • Shape, size, material, position and rotation can be parameterized, by implementing a concrete class of G4VPVParameterisation. • Reduction of memory consumption • G4PVReplica 1 Replica = Many Volumes • Slicing a volume into smaller pieces (if it has a symmetry) • G4ReflectionFactory 1 Placement = a set of Volumes • Generating a pair of placements of a volume and its reflected volume • Useful typically for end-cap calorimeter • G4AssemblyVolume 1 Placement = a set of Placements • Position a group of volumes Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  19. Smart voxelization • In case of Geant 3.21, the user had to carefully implement his/her geometry to maximize the performance of geometrical navigation. • While in Geant4, user’s geometry is automatically optimized to most suitable to the navigation. - "Voxelization" • For each mother volume, one-dimensional virtual division is performed. • Subdivisions (slices) containing same volumes are gathered into one. • Additional division again using second and/or third Cartesian axes, if needed. • "Smart voxels" are computed at initialisation time • When the detector geometry is closed • Does not require large memory or computing resources • At tracking time, searching is done in a hierarchy of virtual divisions Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  20. Geometry checking tools • An overlapping volume is a contained volume which actually protrudes from its mother volume • Volumes are also often positioned in a same volume with the intent of not provoking intersections between themselves. When volumes in a common mother actually intersect themselves are defined as overlapping • Geant4 does not allow for malformed geometries • The problem of detecting overlaps between volumes is bounded by the complexity of the solid models description • Utilities are provided for detecting wrong positioning • Graphical tools • Kernel run-time commands Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  21. Physics

  22. Physics processes in Geant4 • Each process can act at any of three space-time intervals • In time - At rest (e.g. decay at rest) • Continuously along a step (e.g. Cherenkov radiation) • At a point - at the end of the step (e.g. decay in flight) • “Along step actions” are applied cumulatively, while others are selectively applied. • A process can have more than one types of action according to its nature. • For example, Ionization process has Along and End step actions • Tracking handles each type of action in turn. • It loops over all processes with such a type of action. • The motivation for creating these categories of actions is to keep the tracking independent of the physics processes. • All seven combinations of actions are possible. • The traditional Continuous, Continuous-Discrete, Discrete and AtRest are found in these cases. • The ordering of processes is important in some cases. • e.g. Multiple scattering affects the step length. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  23. Electromagnetic processes • Gammas : • Gamma-conversion, Compton scattering, Photo-electric effect • Leptons (e, m), charged hadrons, ions : • Energy loss (Ionisation, Bremstrahlung) or PAI model energy loss, Multiple scattering, Transition radiation, Synchrotron radiation, • Optical photons : • Cerenkov, Rayleigh, Reflection, Refraction, Absorption, Scintillation • High energy m • Alternative implementation • Standard EM package ignores the binding energy of electron to an atom, while Low Energy EM package takes it into account. • ‘Standard’ for applications that do not need to go below 1 KeV • ‘Low Energy’: down to 250eV (e+/g), O(0.1mm) for hadrons Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  24. Multiple scattering • Examples of comparisons: • 15.7 MeV e- on gold foil Modelling & comparisons: L. Urban Angle (deg) Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  25. Hadronic and Photolepton-hadron processes • Each hadronic process may have one or more cross section data sets, and final state production models associated with it. Each one has its own energy range of applicability. • The term “data set” is meant in a broad sense to be an object that encapsulates methods and data for calculating total cross sections. • The term “model” is meant in a broad sense to be an object that encapsulates methods and data for calculating final state products. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  26. Parameterization and data driven models • Parameterization models on the fly • high energy inelastic (Aachen, CERN) • low energy inelastic, elastic, fission, capture (TRIUMF, UBC, CERN, SLAC) • Parameterization models for 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) • 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.. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  27. 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 model (CERN) • Pythia(7) interface (Lund, CERN) • Intra-nuclear transport models (or replacements) • Hadronic cascade+pre-equilibrium model (HIP, CERN) • Binary and Bertini cascade models (HIP, CERN, Novosibirsk, SLAC) • QMD type models (CERN, Inst.Th.Phys. Frankfurt) • Chiral invariant phase-space decay model (JLAB, CERN, ITEP) • Partial Mars rewrite (Kyoto, Uvic, in collaboration with FNAL) • De-excitation • Evaporation, fission, multi-fragmentation, fermi-break-up (CMS) Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  28. Hadronic Model Inventory CHIPS At rest Absorption m, p, K, anti-p CHIPS (gamma) Photo-nuclear, electro-nuclear High precision neutron Evaporation FTF String (up to 20 TeV) Fermi breakup Pre- compound Multifragment Bertini cascade QG String (up to 100 TeV) Photon Evap Binary cascade Fission Rad. decay MARS LE pp, pn HEP ( up to 20 TeV) LEP 1 MeV 10 MeV 100 MeV 1 GeV 10 GeV 100 GeV 1 TeV Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  29. Verification • The verification effort of the geant4 hadronic working group is grouped into several sections: • Inclusive cross-sections • Thin target comparisons • Verification of model components • Code comparisons (least effective) • Complete application tests • Robustness. • A few examples of each are given in the following slides. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  30. Proton reaction total cross-section: J.P.Wellisch Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  31. Pion production examples, QGS:Rapidity distributions and invariant cross-section predictions in quark gluon string model 400GeV protons on Lithium 100 GeV pi+ on Gold Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  32. Lead Forward peaks in proton induced neutron production Beryllium 256 MeV data Neutrons at 7.5deg. Iron Aluminum Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  33. Production from 730 MeV p (Bertini Model) Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  34. Low energy neutron capture:gammas from 14 MeV capture on Uranium Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  35. Nuclear interactions with Geant4 versus experiment 10-9 pC/incident proton Channel Phantom and experimental results from H.Paganetti, B.Gottschalk, Medical physics Vol. 30, No.7, 2003 Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  36. Atlas HEC (e/p ratio) Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  37. CMS ECAL + HCAL testbeam GEANT3 - GEANT4 comparison 100 GeV pi+ ECAL+HCAL Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  38. "Educated guess" physics lists • In Geant4, the physics lists serve the same purpose as the "packages" (GHEISHA, FLUKA, GCALOR) in geant3. • Conceptually, the two are identical. • Both ways provide the physics and its modeling to an application. • Each "package" is built of a complete and consistent set of models • In Geant4, the number of "packages" is quite large. Each option comes with trade-offs in descriptive power and performance. • It simply became clear that writing a good physics list is not 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 the user and to exploit it in the best possible way, but being forced to understand everything is (very understandably) not what people want, either. • We have systematically accumulated experience with various combinations of cross-section and models over the past years. Today we provide a set of physics lists institutionalizing this knowledge. • "Educated guess" physics lists Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  39. LCG simulation project. HEP calorimetry. HEP trackers. 'Average' collider detector Low energy dosimetric applications with 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 low background experiments Air shower applications (still working on this) Each package has several physics lists suitable to the use-case Use-case driven packages Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  40. Decay • A decay table is associated to the definition of each particle type. • A track can have a decay channel. If it has, it exactly decays through this channel without randomizing by the decay ratio. • This allows the user to import decay chains generated by physics generators such as Pythia, and rely on Geant4 tracking for such unstable particles. Primary particle list G4Track B0 B0 K0L … “pre-defined” decay channel K0L … Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  41. Optical processes • Geant4 has a particle named “Optical Photon”, which is distinguished from gamma. It interacts by optical processes. • Geant4 is an ideal framework for modeling the optics of scintillation and Cerenkov detectors and their associated light guides. This is founded in the toolkit's unique capability of commencing the simulation with the propagation of a charged particle and completing it with the detection of the ensuing optical photons on photo sensitive areas, all within the same event loop. • This functionality is now employed world-wide in experimental simulations as diverse as ALICE, ANTARES, AMANDA, Borexino, Icarus, LHCb, HARP, KOPIO, the Pierre Auger Observatory, and the GATE (Imaging in Nuclear Medicine) Collaboration. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  42. Optical processes • Optical photons are generated if one or more of following processes are activated. • Cerenkov radiation, • Transition radiation, • Scintillation • Optical processes built in Geant4 • Absorption, • Rayleigh scattering • Boundary Processes (reflection, refraction) • Optical properties, e.g. dielectric coefficient and surface smoothness, can be set to a volume. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  43. Shower parameterization framework • Geant4 includes a built-in framework for shower parameterization scheme. Currently, the user has to concrete his/her own parameterization assigned to a logical volume, which is then called as an “envelop”. • Regardless of the existence of granular daughter geometry, a particle comes into the envelop can be fully treated by the shower parameterization process. • The user still have a dynamic choice to take his/her parameterization or to follow the ordinary tracking in the granular geometry. • The shower parameterization process can directly contact to a sensitive detector associating to the volume to produce more than one distributed hits. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  44. Highlights ofnew developments

  45. Event biasing in Geant4 • Event biasing (variance reduction) technique is one of the most important requirements, which Geant4 collaboration is aware of. • This feature could be utilized by many application fields such as • Radiation shielding • Dosimetry • Since Geant4 is a toolkit and also all source code is open, the user can do whatever he/she wants. • CMS, ESA, Alice, and some other experiments have already had their own implementations of event biasing options. • It’s much better and convenient for the user if Geant4 itself provides most commonly used event biasing techniques. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  46. Current features in Geant4 • Partial MARS migration • n, p, pi, K (< 5 GeV) • Since Geant4 0.0 • General particle source module • Primary particle biasing • Since Geant4 3.0 • Radioactive decay module • Physics process biasing in terms of decay products and momentum distribution • Since Geant4 3.0 • Cross-section biasing (partial) for hadronic physics • Since Geant4 3.0 • Leading particle biasing • Since Geant4 4.0 • Geometry based biasing • Weight associating with real volume or artificial volume • Since Geant4 5.0 Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  47. I = 1.0 I = 2.0 W=0.5 W=0.5 W=1.0 P = 0.5 Geometrical importance biasing • Define importance for each geometrical region • Duplicate a track with half (or relative) weight if it goes toward more important region. • Russian-roulette in another direction. • Scoring particle flux with weights • At the surface of volumes Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  48. Cuts per Region • Geant4 has had a unique and uniform production threshold (‘cut’) expressed in length (range of secondary). • For all volumes • One cut in range for each particle • By default is the same cut for all particles. • Consistency of the physics simulated • A volume with dense material will not dominate the simulation time at the expense of sensitive volumes with light material. • Yet appropriate length scales can vary greatly between different areas of a large detector • E.g. a vertex detector (5 mm) and a muon detector (2.5 cm). • Having a unique (low) cut can create a performance penalty. • Requests from ATLAS, BABAR, CMS, LHCb, …, to allow several cuts • Enabling the tuning of production thresholds at the level of a sub-detector, i.e. region. • Cuts are applied only for gamma, electron and positron. • ‘Full release’ in Geant4 5.1 (end April, 2003) • Comparable run-time performance compared to global cuts. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  49. Default Region Region B Region B Region B Region A C C Region B Region • Introducing the concept of region. • Set of geometry volumes, typically of a sub-system; • Or any group of volumes; • A cut in range is associated to a region; • a different range cut for each particle is allowed in a region. • Typical Uses • barrel + end-caps of the calorimeter can be a region; • “Deep” areas of support structures can be a region. Geant4 : a simulation toolkit - M.Asai (SLAC) - Dec 01, 2003 @ACAT03

  50. Highlights ofUsers Applications

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