Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University

1. Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University Overview of the Object Oriented Simulation ToolkitMaria Grazia PiaINFN Genova, Italy Maria.Grazia.Pia@cern.chon behalf of the Geant4 Collaboration

2. designof the experimental set-up evaluation and definition of the potential physics output of the project evaluation of potentialrisksto the project assessment of the performance of the experiment development, test and optimisation of reconstruction and physics analysis software contribution to the calculation and validation of physics results The scope of Geant4 encompasses the simulation of the passage of particles through matter there are other kinds of simulation components, such as physics event generators, detector/electronics response generators, etc. often the simulation of a complex experiment consists of several of these components interfaced to one another The role of simulation Simulation plays a fundamental role in various domains and phases of an experimental physics project

3. The zoo NMTC HERMES FLUKA EA-MC DPM SCALE GEM MF3D EGS4, EGS5, EGSnrc MCNP, MCNPX, A3MCNP, MCNP-DSP, MCNP4B Penelope Geant3, Geant4 Tripoli-3, Tripoli-3 A, Tripoli-4 Peregrine MVP, MVP-BURN MARS MCU MORSE TRAX MONK MCBEND VMC++ LAHET RTS&T-2000 ...and I probably forgot some more Many codes not publicly distributed A lot of business around MC Monte Carlo codes presented at the MC200 Conference, Lisbon, October 2000

4. Pro: the specific issue is treated in great detail sometimes the package is based on a wealth of specific experimental data simple code, usually relatively easy to install and use Contra: a typical experiment covers many domains, not just one domains are often inter-connected Pro: the same environment provides all the functionality Contra: it is more difficult to ensure detailed coverage of all the components at the same high quality level monolithic: take all or nothing limited or no options for alternative models usually complex to install and use difficult maintenance and evolution Integrated suites vs specialised codes Specialised packages cover a specific simulation domain Integrated packages cover all/many simulation domains

5. The Toolkit approach A toolkit is a set of compatible components • each component is specialised for a specific functionality • each component can be refined independently to a great detail • components can be integrated at any degree of complexity • components can work together to handle inter-connected domains • it is easy to provide (and use) alternative components • the simulation application can be customised by the user according to his/her needs • maintenance and evolution - both of the components and of the user application - is greatly facilitated ...but what is the price to pay? • the user is invested of a greater responsibility • he/she must critically evaluate and decide what he/she needs and wants to use

6. The Geant approach Geant provides a general infrastructure for • the description of geometry and materials • particle transport and interaction with matter • the description of detector response • visualisation of geometries, tracks and hits The user develops the specific code for • the primary event generator • the geometrical description of the set-up • the digitisation of the detector response

7. Geant4 is a simulation Toolkit designed for a variety of applications It has been developed and is maintained by an international collaboration of > 100 scientists RD44 Collaboration Geant4 Collaboration The code is publicly distributed from the WWW, together with ample documentation 1st production release: end 1998 2 new releases/year since then It provides a complete set of tools for all the typical domains of simulation geometry and materials tracking detector response run, event and track management PDG-compliant particle management visualisation user interface persistency physics processes It is also complemented by specific modules for space science applications

8. Atlas, BaBar, CMS, HARP, LHCB CERN, JNL,KEK, SLAC, TRIUMF Barcelona Univ., ESA, Frankfurt Univ.,Helsinki Univ. IGD, IN2P3, Karolinska Inst., Lebedev, TERA COMMON (Serpukov, Novosibirsk, Pittsburg etc.) Collaboration Board manages resources and responsibilities Technical Steering Board manages scientific and technical matters Working Groups do maintenance, development, QA, etc. Geant4 Collaboration • New organization for the production phase, MoU based • Distribution, development and User Support Members of National Institutes, Laboratories and Experiments participating in Geant4 Collaboration acquire the right to the Production Service and User Support For others: free code and user support on best effort basis Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University

9. Use of Standards • de jure and de facto Geant4 architecture Software Engineering plays a fundamental role in Geant4 • formally collected • systematically updated • PSS-05 standard User Requirements Domain decomposition has led to a hierarchical structure of sub-domains linked by a uni-directional flow of dependencies Software Process • spiral iterative approach • regular assessments and improvements • monitored following the ISO 15504 model • OOAD • use of CASE tools ObjectOriented methods • essential for distributed parallel development • contribute to the transparency of physics • commercial tools • code inspections • automatic checks of coding guidelines • testing procedures at unit and integration level • dedicated testing team QualityAssurance

10. Units Geant4 is independent from the system of units all numerical quantities expressed with their units explicitly user not constrained to use any specific system of units Standards Geant4 adopts standards, ISO and de facto • OpenGL e VRMLfor graphics • CVSfor code management • C++as programminglanguage • STEP engineering and CAD systems • ODMG RD45 Have you heard of the “incident” with NASA’s Mars Climate Orbiter ($125 million)?

11. Data libraries • Systematic collection and evaluation of experimental data from many sources worldwide • Databases • ENDF/B, JENDL, FENDL, CENDL, ENSDF,JEF, BROND, EFF, MENDL, IRDF, SAID, EPDL, EEDL, EADL, SANDIA, ICRU etc. • Collaborating distribution centres • NEA, LLNL, BNL, KEK, IAEA, IHEP, TRIUMF, FNAL, Helsinki, Durham, Japan etc. • The use of evaluated data is important for the validation of physics results of the experiments

12. Platforms DEC, HP, IMB-AIX, SUN, (SGI): native compilers, g++ Linux: g++ Windows-NT: Visual C++ Commercial software ObjectStore STL (optional) Free software CVS gmake, g++ CLHEP Graphics OpenGL, X11, OpenInventor, DAWN, VRML... OPACS, GAG, MOMO... Persistence it is possible to run in transient mode in persistent mode use a HepDB interface, ODMG standard What is needed to run Geant4

13. Run and event the RunManager can handle multiple events possibility to handle the pile-up multiple runs in the same job with different geometries, materials etc. powerful stacking mechanism three levels by default: handle trigger studies, loopers etc. Tracking decoupled from physics: all processes handled through the same abstract interface tracking is independent from particle type it is possible to add new physics processes without affecting the tracking The kernel • Geant4 has only production thresholds, no tracking cuts • all particles are tracked down to zero range • energy, TOF ... cuts can be defined by the user

14. Multiple representations CSG(Constructed Solid Geometries) simple solids STEP extensions polyhedra,, spheres, cylinders, cones, toroids, etc. BREPS(Boundary REPresented Solids) volumes defined by boundary surfaces include solids defined by NURBS (Non-Uniform Rational B-Splines) CAD exchange interface through ISO STEP (Standard for the Exchange of Product Model Data) Fields of variable non-uniformity and differentiability use of various integrators, beyond Runge-Kutta time of flight correction along particle transport Geometry Role: detailed detector description and efficient navigation External tool for g3tog4 geometry conversion

15. Things one can do with Geant4 geometry One can do operations with solids These figures were visualised with Geant4 Ray Tracing tool ...and one can describe complex geometries, like Atlas silicon detectors

16. Chandra(NASA) A selection of geometry applications BaBar at SLAC XMM-Newton (ESA) GLAST (NASA) ATLAS at LHC, CERN CMSat LHC, CERN Borexino at Gran Sasso Lab.

17. Physics • From the Minutes of LCB (LHCC Computing Board) meeting on 21 October, 1997: “It was noted that experiments have requirements for independent, alternative physics models. In Geant4 these models, differently from the concept of packages, allow the user to understand how the results are produced, and hence improve the physics validation. Geant4 is developed with a modular architecture and is the ideal framework where existing components are integrated and new models continue to be developed.”

18. OOD allows to implement or modify any physics process without changing other parts of the software open to extension and evolution Tracking is independent from the physics processes The generation of the final state is independent from the access and use of cross sections Transparent access via virtual functions to cross sections (formulae, data sets etc.) models underlying physics processes An abundant set of electromagnetic and hadronic physics processes a variety of complementary and alternative physics models for most processes Use of public evaluated databases No tracking cuts, only production thresholds thresholds for producing secondaries are expressed in range, universal for all media converted into energy for each particle and material Features of Geant4 Physics The transparency of the physics implementation contributes to the validation of experimental physics results

19. Processes Processes describe how particles interact with material or with a volume itself Three basic types • At rest process • (e.g. decay at rest) • Continuous process • (e.g. ionization) • Discrete process • (e.g. decay in flight) Transportationis a process • interacting with volume boundary The process which requires the shortest interaction length limits the step

20. multiple scattering Bremsstrahlung ionisation annihilation photoelectric effect Compton scattering Rayleigh effect g conversion e+e- pair production synchrotron radiation transition radiation Cherenkov refraction reflection absorption scintillation fluorescence Auger(in progress) Comparable to Geant3 already in the 1st a release (1997) High energy extensions fundamental for LHC experiments, cosmic ray experiments etc. Low energy extensions fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. Alternative models for the same physics process Electromagnetic physics • It handles • electrons and positrons • g, X-ray and optical photons • muons • charged hadrons • ions energy loss

21. Photo Absorption Ionisation Model Ionisation energy loss produced by charged particles in thin layers of absorbers 3 GeV/c p in 1.5 cm Ar+CH4 5 GeV/c p in 20.5 mm Si Ionisation energy loss distribution produced by pions, PAI model

22. Muon processes • Validity range 1 keV up to 10 PeV scale •  simulation of ultra-high energy and cosmic ray physics • High energy extensions based on theoretical models • Bremsstrahlung • Ionisation and d ray production • e+e- Pair production

23. Processes for optical photons • Optical photon  its wavelength is much greater than the typical atomic spacing • Production of optical photons in HEP detectors is mainly due to Cherenkov effect and scintillation • Processes in Geant4 • in-flight absorption • Rayleigh scattering • medium-boundary interactions (reflection, refraction) Track of a photon entering a light concentrator CTF-Borexino

24. Hadronic physics Relevant features • theory-driven, parameterisation-driven, data-driven models • complementary and alternative models Cross section data sets • transparent and interchangeable Final state calculation • models by particle, energy, material

25. Based on experimental data Some models originally from GHEISHA completely reengineered into OO design refined physics parameterisations New parameterisations pp, elastic differential cross section nN, total cross section pN, total cross section np, elastic differential cross section N, total cross section N, coherent elastic scattering Hadronic physicsParameterised and data-driven models (1) p elastic scattering on Hydrogen

26. Other models are completely new, such as stopping particles (- , K- ) neutron transport isotope production Stopping p absorption Neutrons Courtesy of CMS nuclear deexcitation MeV Energy Hadronic physicsParameterised and data-driven models (2) • Alldatabases existing worldwide used in neutron transport • Brond, CENDL, EFF, ENDFB, JEF, JENDL, MENDL etc.

27. Hadronic physicsTheoretical models • They fall into different parts • the evaporation phase • the low energy range, pre-equilibrium, O(100 MeV), • the intermediate energy range, O(100 MeV) to O(5 GeV), intra-nuclear transport • the high energy range, hadronic generator régime • Geant4 provides complementary theoretical models to cover all the various parts • Geant4 provides alternative models within the same part • All this is made possible by the powerful Object Oriented design of Geant4 hadronic physics • Easy evolution: new models can be easily added, existing models can be extended

28. A sample from theory-driven models

29. Materials elements, isotopes, compounds, chemical formulae Particles all PDG data and more, for specific Geant4 use, like ions Hits & Digi to describe detector response Persistency possibility to run in transient or persistent mode no dependence on any specific persistency model persistency handled through abstract interfaces to ODBMS Visualisation Various drivers OpenGL, OpenInventor, X11, Postscript, DAWN, OPACS, VRML User Interfaces Command-line, Tcl/Tk, Tcl/Java, batch+macros, OPACS, GAG, MOMO automatic code generation for geometry and materials Interface to Event Generators through ASCII file for generators supporting /HEPEVT/ abstract interface to Lund++ Other components

30. Modules for space applications General purpose source particle module Delayed radioactivity INTEGRAL and other science missions Low-energy e.m. extensions Particle source and spectrum Geological surveys Sector Shielding Analysis Tool CAD tool front-end Instrument design purposes Dose calculations

31. Fast simulation • Geant4 allows to perform full simulation and fast simulationin the same environment • Geant4parameterisationproduces a direct detector response, from the knowledge of particle and volume properties • hits, digis, reconstructed-like objects (tracks, clusters etc.) • Great flexibility • activate fast /full simulation by detector • example:full simulation for inner detectors, fast simulation per calorimeters • activate fast /full simulation by geometry region • example:fast simulation in central areas and full simulation near cracks • activate fast /full simulation by particle type • example:in e.m. calorimeter e/ parameterisation and full simulation of hadrons • parallel geometries in fast/full simulation • example: inner and outer tracking detectors distinct in full simulation, but handled together in fast simulation

32. Performance • Various Geant4 - Geant3.21 comparisons • realistic detector configurations • results and plots in • Geant4 Web Gallery (from Geant4 homepage) • RD44 Status Report, 1995 • Benchmark in liquid Argon/Pb calorimeter • at comparable physics performance Geant4 is faster than (fully optimised) Geant3.21 by • a factor >3 using exactly the same cuts • a factor >10 optimising Geant4 cuts, while keeping the same physics performance • at comparable speed Geant4 physics performance is greatly superior to Geant3.21 • Benchmark in thin silicon layer • at comparable physics performance Geant4 is 25% faster than Geant3.21 (single volume, single material)

33. User Documentation Introduction to Geant4 Installation Guide Application Developer Guide Toolkit Developer Guide Software Reference Manual Physics Reference Manual Examples a set of Novice, Extended and Advanced examples illustrating the main functionalities of Geant4 in realistic set-ups The Gallery a web collection of performance and physics evaluations http://cern.ch/geant4/reports/gallery/ Publication and Results web page http://cern.ch/geant4/reports/reports.html Low Energy e.m. Physics http:www.ge.infn.it/geant4/lowE Documentation http://cern.ch/geant4/geant4.html Seminars and Training courses available

34. The software challenge first successful attempt to redesign a major package of HEP software adopting an Object Oriented environment and a rigorous approach to advanced software engineering The functionality challenge a variety of requirements from many application domains (HEP, space, medical etc.) The physics challenge transparency extended coverage of physics processes across a wide energy range, with alternative models The performance challenge mandatory for large scale HEP experiments and for other complex applications The distributed software development OOAD has provided the framework for distributed parallel development The management challenge a well defined, and continuously improving, software process has allowed to achieve the goals The user support challenge the user community is distributed worldwide, operating in a variety of domains Conclusions Geant4 has successfully coped with a variety of challenges

35. Geant4 review • Next week at CERN • External review to evaluate Geant4 activity in 1999-2000 • Chairman: U. Mortensen (ESA) • Part 1 • Presentation of the activity of Geant4 Collaboration in 1999-2000 • (functionalities, user support etc.) • Part 2 • Results of applications from user groups (mainly comparisons with data) • Feedback on user support • Not a channel to present user requirements • User requirements should be conveyed through the normal User Support path (TSB Representatives) • TSB Representatives attending this Round Table: • V. Ivanchenko (Novosibirsk, Common), P. Nieminen (ESA), M.G. Pia (INFN), P. Truscott (DERA)