Geant4: an update

1. Geant4: an update John Apostolakis, CERN Makoto Asai, SLAC for the Geant4collaboration Version 0.5.4 23rd March 2003, 16:30

2. Outline • Brief introduction to Geant4 • Physics highlights • Modeling • validation • New capabilities • Detector description and collision detection • Some of the Developments • In progress • Planned for 2003

3. GEANT 4 • Detector simulation tool-kit for HEP • offering alternatives, allowing for tailoring • Software Engineering and OO technology • provide the method for building, maintaining it. • Requirements from: • LHC • heavy ions, CP violation, cosmic rays • medical and space science applications • World-wide collaboration

4. Geant4 Capabilities • Extensive & transparent physics models • electromagnetic, hadronic, optical, decay, … • Powerful structure and kernel • tracking, stacks, geometry, hits, … • Interfaces • visualization, GUI, persistency. • Efficiency enhancing techniques • Framework for fast simulation (shower parameterization) • Variance reduction / event biasing

5. Physics Development Highlights Geant4 releases Dec 2001-today included • New theoretical hadronic models • CHIPS for g-Nucleus, p capture, .. • Cascade models: Bertini (HETC) and Binary • New EM processes • gto m pair • new TR models • Numerous physics improvements Including, for example • Charge state for recoils • Improved X-sections for e-Nuclear, with hard scattering

6. Multiple scattering • Examples of comparisons: • 15.7 MeV e- on gold foil (figure this page) Modelling & comparisons: L. Urban Angle (deg)

7. Multiple scattering • Examples of comparisons: • 15.7 MeV e- on gold foil Modelling & comparisons: L. Urban Angle (deg)

8. Significant developments in EM (std) in 2002 • Multiple scattering (L. Urban) • Ultra relativistic energies (H. Burkardt, S. Kelner, R. Kokoulin) • Ionization for Generic Ions (V. Ivanchenko) • Models of Transition radiation detectors (V. Grichine) • Redesign of few processes: prototype model approach for Ionization and Bremsstrahlung (V. Ivanchenko)

9. Comparison projects • Joint efforts for comparing Geant4 with experiment & test-beam data. • Results of EM comparisons: 2000-2002. • Hadronic comparisons: 2002-ongoing. • Collaboration with experiments • ATLAS (projects with data of test beams of 4 calorimeters) • BaBar (with experiment data for tracker, drift chamber) • Many results have been presented (by the experiments) at conferences & workshops eg Calor 2002. • Presentations at quarterly LHC experiment-Geant4 physics comparisons meetings, eg 4th March 2003.

10. Element particle Energy CHIPS QGSM Hadronic physics: models, processes and ‘lists’ Components can be assembled in an optimized way for each use case. • Five level implementation framework • Variety of models and cross-sections • for each energy regime, particle type, material • alternatives with different strengths and CPU requirements. • Illustrative example of assembling models into an inelastic process for set of particles • Uses levels 1 & 2 of framework Z Pre-compound model Parame- terized

11. Models: Cascade energy range • Parameterized process (1997) • Chiral Invariant Phase Space decay,“CHIPS” • Development 2000-2001 (M Kosov, P Degtyarenko, JP Wellisch) • Refinements and extension in 2002 • Bertini cascade (Dec 2002, Geant4 5.0) • Re-engineered from HETC, • See the presentation of A Heikinen • Binary cascade model (Frankfurt, CERN) • First release for nucleon induced interactions (in Geant4 5.0) • Extensive verification suite • See the presentation by D. Wright • For other details, • see the next presentation (J.P. Wellisch)

12. Tailored Physics ‘lists’ • Created and distribute “educated guess” physics lists • That correspond to the major use cases of Geant4 involving hadronic physics, • to use directly, and as a starting point for users to modify, • facilitate the specialization of those parts of hadronic physics lists that vary between use cases. • First released in September 2002 • Using physics models of Geant4 4.1. • Revised with experience of comparisons with data • Latest: • updated with physics models of Geant4 5.0 in March 2003 • Find them on the G4 hadronic physics web pages http://cmsdoc.cern.ch/~hpw/GHAD/HomePage

13. Calorimetry Tracker detectors Average HEP detector High energy physics calorimetry. High energy physics trackers. 'Average' HEP 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 low background experiments Use cases of Physics Lists Contributors: http://cern.ch/geant4/organisation/ working_groups.html#wg.Had

14. Resolution Original (org) results from Calor 2002 presentation, (March 2002). Open symbols from additional physics lists JPW, May 2002, using geant4 4.0-patch2 (released: end Feb 2002). Status of May 2002 Thanks to Atlas HEC and J.P. Wellisch

15. BaBar Geant4 based simulation since 2001 production. More than 109 events (through Oct 2002) Used Geant4 3.1+fixes, own transport.

16. Other Development highlights • Various improvements • Ability to reduce initialisation time • By saving/retrieving physics processes’ table • A different field for any volume (or volume tree) • Overriding a potential global ‘default’ field • Additional ways to create geometries • Detect and debug incorrect geometry definitions • Variance reduction • Importance: biasing by geometry • In real or ’ghost’ geometry • Eg enabling simulation of shielding applications with improved time efficiency by large factors • Leading particle biasing • a-la MARS 95, for En<5GeV

17. Improvements in Geometry • Reflection of volume hierarchies • Eg to create endcap geometry • Improved voxelisation for performant navigation • 3-D for parameterized volumes • Now equal performance to ‘placed’ volume • Option to avoid voxelising some volumes • ‘Illegal’ geometries detected & rejected • E.g. incompatible daughters (placed & parameterised) • XML binding: GDML 1.0 released • Specification • Implementation • Refinements currently on ‘hold’. I Hrivnacova G Cosmo V Grichine G Cosmo R Chytracek

18. Debugging geometries • It is easy to create overlapping volumes • a volume that protrudes from its mother, • 2+ volumes that intersect in common mother • During tracking Geant4 does not check for malformed geometries • The problem of detecting ‘significant’overlaps is now addressed by • DAVID that intersects volumes directly • Uses graphical representations • By S. Tanaka, released circa 1997 • New built-in run-time commands to run verification tests by its own navigation • Using solids and a grid of rays • Created DC Williams; released in 4.0 • New example with full tracking / navigation • Uses the full hierarchy & the Navigator • Created by M Liendl; released in 5.0 Thanks to S. Tanaka

19. Variance reduction • Geant4 has had an event biasing option for the transportation of “low energy” neutrons. • The formulae are derived from MARS95. • New, redesigned and improved, implementation in Geant4 4.1. • It was possible to use other methods, but only in user code. • Now new general purpose built-in methods have been created. • Importance biasing: • Splitting/Russian roulette (first released in G4 4.1, June 2002). • Importance values can be associated to a ‘mass’ geometry or to a ghost geometry. • Varied options in driving MC ‘history’ and scoring tallies; • No changes to the kernel were required, due to the flexibility of the toolkit. M Dressel

20. CPU Performance • Our simple benchmarks: • Geometry faster, EM shower setups: competitive • Performance in experimental setups (with Geant4 releases 2 and 3) was comparable to Geant3 • few counterexamples, including BTeV ECAL. • New performance issue arose with Geant4 4.0 • and were addressed (in the patches & release 4.1) • Difficult cases remain, including • Some setups of EM showers and field propagation, factor ~ 2x • Collecting a set of benchmarks • To follow computing performance regularly • Goal is that Geant4 is at least as fast as Geant3 in almost all cases • When its power is used.

21. DAWN renderer Thanks to S. Tanaka Visualization Geometry, hits • New • “DTREE”: hierarchy display • HEPREP and Wired driver • Other Current Drivers • OpenGL • Popular, hardware speed • VRML • Portable, lower detail • DAWN renderer • High quality Postscript • Also from others, eg • IGUANA (for CMS simulation) Iguana, thanks to L.Tuura, I. Osborne

22. In Progress 2003 (highlights) • Cuts per region • See next slides • Improvements of multiple scattering • in straggling, backscattering • Additional refinements of physics lists • Continuous updates • Design iteration of EM (std) processes • With benefits in tailoring, maintenance • Further extension and automation of testing • Statistical testing: ‘benchmarks’ and test-beams

23. Cuts per region (precis) • Geant4 has had a unique production threshold (‘cut’) expressed in length (range of secondary). • For all volumes • Possibly different for each particle. • This promotes • Good consistency in energy deposition • less use of CPU in dense materials (compared to a common Energy) • Yet appropriate length scales can vary greatly between different areas of a large detector • Eg a vertex detector (5 mm) and a muon detector (2.5 cm). • Having a unique (low) cut can create a performance penalty. • New functionality, • enabling the tuning of production thresholds at the level of a sub-detector. • Created Region (or sub-detector)

24. Cuts/Region Introduction • A Cut here is a « production threshold »; • Only for physics processes that have infra-red divergence • Not tracking cut; (which does not exist in Geant4) • GEANT4 up to now allows a unique cut in range; • 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. • Requests from ATLAS, BABAR, CMS, LHCb, …, to allow several cuts; • Globally or per particle;

25. Motivation for several cuts • Having a unique cut can be the source of performance penalties; • Part of the detector with lower cut needs fixes the cut for the all simulation; • Can be far too low than necessary in other parts; • Silicon vertex detector: a few 10 mm; • Hadronic calorimeter: 1 cm; • Other parts being geometrically far, to.

26. Region: example & properties • Introduce the concept of « region »: • Set of geometry volumes, typically of a sub-system; • Eg: barrel + end-caps of the calorimeter; • 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. Region B Region B Region B Region C c Region B Region A

27. Cuts per region status • Design and implementation have been made • without severe design revision of the existing GEANT4; • First implementation available in latest b release (Feb) • Comparable run-time performance • Today a penalty within 5% is seen, due to redundant checks included for verification purposes • ‘Full release’ will be in Geant4 5.1 (end April) • With further refinements, tests, validation.

28. In progress (also) • The refinement of the design of EM physics processes through the use of ‘models’. • To enable the specialization of key features; • To enable the easy use of different models for a single process (e.g. Ionization) in one application. • Additional variance reduction techniques • Filter for enhancing processes in hadronic interactions.

29. Scheduled 2003 Development: highlights • Cuts per region • Additional physics processes/models • Hadronic: p induced binary cascade model, .. • EM: refinements to multiple scattering; “models”. • Refinements, including • Improvement to recoil in elastic scattering • Improved X-sections for pions. • Variance reduction • Physics process enhancement • Refinements to importance biasing. • Leading particle

30. Geant4 Collaboration Collaborators also from non-member institutions, including Budker Inst. of Physics IHEP Protvino MEPHI Moscow Lebedev

31. Review and Releases • d Review October 2002 • Report available at http://cern.ch/geant4 • Developments available in b releases • Every two months • Latest b release (February) • Included cuts per region • Upcoming releases • Planned: Geant4 5.1 release end-April • Geant4 5.2 scheduled for end-June • Release timeframe(s) adjusted for customer needs • Workplan • User & Experiment Requirements and Requests • Next major release Geant4 6.0 scheduled for December.

32. http://cern.ch/geant4/ Summary • Results of comparing Geant4 versus data, • Have & are providing excellent ‘yardsticks’ of EM perf. • Are testing the hadronics well, with increasing coverage • Geant4 has demonstrated important strengths: • stability of results, flexibility, transparency. • Geant4 is in production use today in running HEP experiments (BaBar, HARP) • Geant4 is evolving • With requirements from LHC exper., BaBar and numerous other experiments and application domains. • Refinements & development are ongoing.

33. THE END Slides after this are backup slides, deleted from the presentation

34. Support: new & continued • Documentation • Revisions of the user and reference guides • After assessments of overall structure & detailed • LXR for code reference • see http://geant4www.triumf.ca/lxr/ • New tool for collecting requirements • Continued Support • of users’ questions, problems • HyperNews, Problem reporting system, email. • of comparisons with data • By wide variety of users, in HEP, space, medical phys., ..

35. Testing and QA 2002/3 • Establishment of ‘statistical testing’ suite • Automated comparison of physics quantities • Against ‘standard’ data (eg NIST) • In ‘test-beam’ applications • Including ‘regression testing’. • For details see • Establishing a benchmark suite for computing performance.

36. Geant4 Capabilities • Extensive & transparent physics models • electromagnetic, hadronic, optical, decay, … • Powerful structure and kernel • tracking, stacks, geometry, hits, … • Interfaces • visualization, GUI, persistency. • Efficiency enhancing techniques • Framework for fast simulation (shower parameterization) • Variance reduction / event biasing

37. Summary • Geant4 is in production use today in running HEP experiments (BaBar, HARP) • Results of comparing Geant4 versus data • are growing month by month, • have provided important ‘yardsticks’. • Geant4 has demonstrated important strengths: • stability of results, flexibility, transparency. • Refinements & development are ongoing.

38. Testing tools • Improvements of tools for automation of testing, followup • Tinderbox • Bonsai • LXR for use in testing followup

39. Examples of improvements Fixes and improvements in Geant4 release 4.1 (June 2002) • Geometry • Fix for voxelisation of reflected volumes • Fix for exit normal angle • Fix for problem in very small step in field • EM • Improvements in Multiple Scattering, Ionisation, .. • Hadronics • Fix for energy conservation in parametrised models. • Fix for small peak at f=0 in parametrised models.