Object Oriented Simulation Toolkit for X-ray Astronomy Missions

1. Overview of the Object Oriented Simulation Toolkit Maria Grazia Pia INFN Genova, Italy and CERN/IT Maria.Grazia.Pia@cern.ch

2. Once upon a time there was a X-ray telescope... Courtesy of NASA/CXC/SAO

3. Chandra X-ray Observatory Status Update September 14, 1999 MSFC/CXC CHANDRA CONTINUES TO TAKE SHARPEST IMAGES EVER; TEAM STUDIES INSTRUMENT DETECTOR CONCERN Normally every complex space facility encounters a few problems during its checkout period; even though Chandra’s has gone very smoothly, the science and engineering team is working a concern with a portion of one science instrument. The team is investigating a reduction in the energy resolution of one of two sets of X-ray detectors in the Advanced Charge-coupled Device Imaging Spectrometer (ACIS) science instrument. A series of diagnostic activities to characterize the degradation, identify possible causes, and test potential remedial procedures is underway. The degradation appeared in the front-side illuminated Charge-Coupled Device (CCD) chips of the ACIS. The instrument’s back-side illuminated chips have shown no reduction in capability and continue to perform flawlessly. An excerpt of a press release Courtesy of NASA/CXC/SAO

4. What can affect CCD’s on X-ray astronomy missions? • Radiation belt electrons? • Scattered in the mirror shells? • Effectiveness of Magnetic “brooms” • Electron damage mechanism? - NIEL? • Other particles? Protons, cosmics • Path to CCD? Wall penetration? • Proposal: set the problem up in Geant4 as a case-study.

5. XMM

6. ESA Space Environment & Effects Analysis Section RGS EPIC Q2 Q1 Q1

7. EPIC RGS ESA Space Environment & Effects Analysis Section CCD displacement damage: front vs. back-illuminated. 30 mm Si  ~1.5 MeV p+ 2 mm 30 mm 2 mm 30 mm Active layerPassive layer “Electron deflector” Low-E (~100 keV to few MeV), low-angle (~0°-5°) proton scattering:Obscure problem; not much analysed

8. How well can Geant4 simulate low energy protons? Courtesy of R. Gotta, Thesis

9. What happened next? XMM was launched on 10 December 1999 from Kourou EPIC image of the two flaring Castor components and the brighter YY Gem Courtesy of

10. What is Geant? Status of Geant3 and motivations for Geant4 The Geant4 R&D phase: RD44 The Geant4 Collaboration The role of software engineering and OO technology Performance A selection of Geant4 applications Conclusions Outline • Main features of the Geant4 toolkit • the kernel • geometry • physics • other tools

11. The role of Geant • Geant is a simulation tool, that 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

12. The past: Geant3 • Geant 3 • has been used by most major HEP experiments • Frozen since March 1994 (Geant3.21) • ~200K lines of code • equivalent of ~50 man-years, along 15 years • used also in nuclear physics experiments, medical physics, radiation background studies, space applications etc. • The result is a complex system • because its problem domain is complex • because it requires flexibility for a variety of applications • because its management and maintenance are complex • It is not self-sufficient • hadronic physics is not native, it is handled through the interface to external packages

13. Very high statistics to be simulated robustness and reliability for large scale production Exchange of CAD detector descriptions Transparent physics for validation of physics results Physics extensions to high energies LHC, cosmic ray experiments... Physics extensions to low energies space applications, medical physics, X-ray analysis, astrophysics, nuclear and atomic physics... Reliable hadronic physics not only for calorimetry, but also for PID applications (CP violation experiments) ...etc. New simulation requirements User requirements formally collected and coded according to PSS05 standard • Geant4 User Requirements Document

14. What is Geant4? • OO toolkit for the simulation of next generation HEP detectors ...of the current generation too ...not only of HEP detectors • already used also in nuclear physics, medical physics, space applications, radiation background studies etc. • It is also an experiment of distributed software production and management, as a large international collaboration with the participation of various experiments, labs and institutes • It is also an experiment of application of rigorous software engineeringandObject Oriented technologies to the HEP environment

15. Milestones: end 1995 OO methodology, problem domain analysis, full OOAD tracking prototype, performance evaluation Milestones: spring 1997 -release with the same functionality as Geant 3.21 persistency (hits), ODBMS transparency of physics models Milestone: July 1998 public -release Milestone: end 1998 production release: Geant4.0, end of the R&D phase All milestones have been met by RD44 Reconfiguration at the end of the R&D phase International Geant4 Collaboration sincel 1/1/1999 Management of the production phase Continuing R&D also in the production phase • Approved as R&D end 1994 (RD44) • > 100 physicits and software engineers • ~ 40 institutes, international collaboration • responded to DRCC/LCB

16. Atlas, BaBar, CMS, HARP, LHCB CERN, JNL,KEK, SLAC, TRIUMF ESA, Frankfurt Univ., IGD, IN2P3, Karolinska Inst., Lebedev, TERA COMMON (Serpukov, Novosibirsk, Pittsburg etc.) other memberships currently being discussed 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

17. Software process based on Booch methodology spiral type, with cycles of design-implementation iterations OOAD Development Evolution Maintenance in a worldwide collaboration! Software Engineering Software Engineering plays a fundamental role in Geant4 • Software process • User requirements • OOAD • Quality Assurance • User Requirements • Collected initially and systematically updated • Coded according to ESA PSS-05 standard

18. OO technologies OO design fundamental for distributed parallel approach • every part can be developed, refined, maintained independently • Problem domain decomposition and OOAD result into a unidirectional dependency of class categories • Open to evolution • extensibility, implementation of new models and algorithms without interfering with existing software • the user can extend the toolkit with his/her model and data • Transparency • decoupling from implementation • Flexibility • alternative models and implementations • Interface to external software, without dependencies • databases for persistency • visualisation libraries • tools for UI • etc.

19. Geant4 architecture exploits advanced Software Engineering techniques and Object Orientedtechnology to achieve transparency of physics implementation.

20. Extensive use of Quality Assurance systems fundamental for a toolkit of wide public use Commercial tools Insure++, Logiscope etc. C++ coding guidelines scripts to verify their applications automatically Code inspections within working groups and across groups Testing Unit testing in most cases down to class level granularity Integration testing sets of logically connected classes Test-bench for each category eg.: test-suite of 375 tests for hadronic physics parameterised models System testing exercising all Geant4 functionalities in realistic set-ups Physics testing comparisons with experimental data Performance Benchmarks Quality Assurance

21. Standards Based on standards, ISO and de facto 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 • OpenGL e VRML for graphics • CVSfor code management • C++ as programming language • STEP • engineering and CAD systems • ODMG • RD45 Have you heard of the “incident” with NASA’s Mars Climate Orbiter ($125 million)?

22. 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

23. The Geant4 kit • Code • ~1M lines of code, ~2000 classes • (continuously growing) • publicly available from the web • Documentation • 6 manuals • publicly available from the web • Examples • distributed with the code • navigation between documentation and examples code

24. Run and event the Run Manager 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

25. Multiple representations CGS (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) External tool for g3tog4 geometry conversion 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

26. 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

27. 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.

28. 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) • Transportation is a process • interacting with volume boundary • A process which requires the shortest interaction length limits the step

29. 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.”

30. The approach to physics • Ample variety of independent, alternative physics models available in Geant4 • No more black boxes of packages • Users are directly exposed to the physics they use in their simulation • This approach is fundamental for the validation of the experiments’ physics results

31. Transparency of Geant4 physics • No “hard coded” numbers • Explicit use of units throughout the code • Separation between the calculation of cross sections and the generation of the final state • Calculation of cross-sections independent from the way they are accessed (data files, analytical formulae etc.) • Distinction between processes and models • Cuts in range(rather than in energy, as usual) • consistent treatment of interactions near boundaries between materials • Modular design, at a fine granularity, to expose the physics • physics independent from tracking • Public distribution of the code, from one reference repository worldwide

32. Physics: general features • Abstract interface to physics processes • tracking independent from processes • Distinction between processes and models • often multiple models for the same process • Data encapsulation and polymorfism • Transparent access to cross sections, from files, interpolation from tables, analytical formulae etc. • Distinction between the calculation of cross sections and their use • Calculation of the final state independent from tracking • Uniform treatment of electromagnetic and hadronic physics • Open system • Users can easily create and use their own models

33. 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

34. Electromagnetic physics • Comparable to Geant3 and EGS already in the -release • Substantial further extensions • Multiple alternatives for various processes • High energy extensions • models for  up to PeV • fundamental for LHC experiments, cosmic ray experiments etc. • Low energy extensions • e, down to 250 eV • (EGS, ITS etc. to 1 keV, Geant3 to 10 keV)) • low energy hadrons and ions models based on Ziegler and ICRU data and parametrisations • models for antiprotons (positrons in progress) • fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc.

35. multiple scattering energy loss Bremsstrahlung ionisation annihilation photoelectric effect Compton scattering pair production synchrotron radiation transition radiation Cherenkov Rayleigh effect rifraction reflection absorption scintillation fluorescence Auger (in progress) E.M. processes in Geant4

36. Selection of e.m. physics results Backscattering Multiple scattering

37. Low energy e.m. extensions Fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. Barkas effect: models for antiprotons e, down to 250 eV (positrons in progress) (EGS, ITS to 1 keV, Geant3 to 10 keV) Low energy hadrons and ions models based on Ziegler and ICRU data and parameterisations

38. ESA Space Environment & Effects Analysis Section Low energy e.m. extensions Cosmic rays, jovian electrons X-Ray Surveys of Asteroids and Moons Solar X-rays, e, p Geant3.21 ITS3.0, EGS4 Courtesy SOHO EIT Geant4 Induced X-ray line emission: indicator of target composition (~100 mm surface layer) C, N, O line emissions included

39. Low energy e.m. extensions Brachytherapy at IST Genova, Italian National Institute for Cancer Research • Photon attenuation coefficient in water • 1.000.000 photons generated, • 120 sec on an Intel PC 300 MHz Courtesy of IST

40. High energy e.m. extensions Models for muons extended up to the PeV scale High energy m Courtesy of L3

41. Examples of application of Geant4 e.m. physics Sampling calorimeter Courtesy of CMS

42. Hadronic physics • Completely different approach w.r.t. the past • transparent • native • no longer interface to external packages • clear separation between data and their use in algorithms • Cross section data sets • transparent and interchangeable • Final state calculation • models by particle, energy, material

43. Completeness of Geant4 hadronic physics • Ample variety of models • the most complete hadronic simulation kit on the market • alternative and complementary models • it is possible to mix-and-match, with fine granularity • data-driven, parameterised and theoretical models • Consequences for the users • no more confined to the black box of one package • the user has control on the physics used in the simulation, which contributes to the validation of physics results

44. 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

45. 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.

46. 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

47. A sample from theory-driven models

48. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 152 cm Copper + 189 mm Plastic An example of user application CMS HCAL (H2 1996) Test-Beam Setup Courtesy of CMS Collaboration

49. Event biasing • Geant4 provides facilities for event biasing • The effect consists in producing a small number of secondaries, which are artificially recognized as a huge number of particles by their statistical weights • Event biasing can be used, for instance, for the transportation of slow neutrons or in the radioactive decay simulation

50. 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