maria grazia pia, infn genova overview of the object oriented simulation toolkit maria grazia pia...

Maria Grazia Pia, INFN Genova

Overview of the

Object Oriented Simulation ToolkitMaria Grazia PiaINFN Genova, Italy

[email protected] behalf of the Geant4 Collaboration

Budker Inst. of PhysicsIHEP ProtvinoMEPHI Moscow Pittsburg University



The role of simulation

designdesign of the experimental set-up evaluation and definition of the

potential physics outputphysics output of the project

evaluation of potential risksrisks to the project

assessment of the performanceperformance of the experiment

development, test and optimisation of reconstructionreconstruction and physics analysis softwareanalysis software

contribution to the calculation and validation of physics results 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

Simulation plays a fundamental role in various domains and phases of an experimental physics project


EGS4, EGS5, EGSnrcMCNP, MCNPX, A3MCNP, MCNP-DSP, MCNP4BPenelopeGeant3, Geant4Tripoli-3, Tripoli-3 A, Tripoli-4 PeregrineMVP, MVP-BURNMARS

MCUMORSETRAXMONKMCBENDVMC++LAHETRTS&T-2000

NMTCHERMES FLUKAEA-MCDPMSCALEGEMMF3D

...and I probably forgot some more

Many codes not publicly distributed

A lot of business around MC

The zoo

Monte Carlo codes presented at the MC200 Conference, Lisbon, October 2000Monte Carlo codes presented at the MC200 Conference, Lisbon, October 2000


Integrated suites vs specialised codes

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

functionalityContra:• 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

Specialised packages cover a specific simulation domain

Integrated packages cover all/many simulation domains


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


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

The Geant approach


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


Geant4 Collaboration

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.

Members of National Institutes, Laboratories and Experiments participating in Geant4 Collaboration acquire the right to the Production Service and User SupportFor others: free code and user support on best effort basis


New organization for the production phase, MoU based Distribution, development and User Support


Software Engineering

plays a fundamental role in Geant4

User Requirements• formally collected• systematically updated• PSS-05 standard

Software Process• spiral iterative approach• regular assessments and improvements• monitored following the ISO 15504 model

Quality Assurance• commercial tools• code inspections• automatic checks of coding guidelines• testing procedures at unit and integration level• dedicated testing team

Object Oriented methods• OOAD• use of CASE tools

• essential for distributed parallel development• contribute to the transparency of physics

Use of Standards • de jure and de facto

Domain decomposition

has led to a hierarchical structure of

sub-domains linked

by a uni-directional

flow of

dependencies

Geant4 architecture


Standards

UnitsUnits• 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

Geant4 adopts standards, ISO and de facto

OpenGL e VRML for graphics

CVS for code management

C++ as programming language

STEPengineering and CAD systems

ODMG RD45

Have you heard of

the “incident” with

NASA’s Mars

Climate Orbiter

($125 million)?


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


What is needed to run Geant4

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


The kernel

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

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


Geometry

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

Role: detailed detector description and efficient navigation

External tool for g3tog4 geometry conversion


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


Borexino at Gran Sasso Lab.

BaBar at SLAC Chandra (NASA)XMM-Newton (ESA)

ATLAS at LHC, CERNGLAST (NASA)

CMS at LHC, CERN

A selection of geometry applications


PhysicsPhysics

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.”


Features of Geant4 Physics OOD allows to implement or modify any

physics process without changing other parts of the software

open to extension and evolutionopen to extension and evolution

Tracking Tracking is independent from the physics processes

The generation of the final statefinal 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 electromagneticelectromagnetic and hadronic hadronic physics processes

a variety of complementary and alternative physics modelsphysics models for most processes

Use of public evaluated evaluated databasesdatabases

No tracking cuts, only production production thresholdsthresholds

thresholds for producing secondaries are expressed in rangerange, universal for all media

converted into energy for each particle and material

The transparency of the physics implementation contributes to the validation of experimental physics results


Processes

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

The process which requires the shortest interaction length limits the step

Processes describe how particles interact with material or with a volume itself


multiple scattering Bremsstrahlung ionisation annihilation photoelectric effect Compton scattering Rayleigh effect conversion e+e- pair production synchrotron radiation transition radiation Cherenkov refraction reflection absorption scintillation fluorescence Auger (in progress)

Electromagnetic physics

Comparable to Geant3 already in the 1st release (1997)

High energy extensionsHigh energy extensions fundamental for LHC experiments, cosmic ray experiments etc.

Low energy extensionsLow energy extensions fundamental for space and medical applications, neutrino

experiments, antimatter spectroscopy etc.

Alternative models for the same physics processAlternative models for the same physics process

energy lossIt handles

electrons and positrons , X-ray and optical photons muons charged hadrons ions


Ionisation energy loss distribution produced by pions, PAI modelPAI model

3 GeV/c in 1.5 cm Ar+CH4 5 GeV/c in 20.5 m Si

PPhoto hoto AAbsorption bsorption IIonisation onisation ModelModel

Ionisation energy loss produced by charged particles in thin layers of absorbers


Muon processes

Validity range

1 keV up to 10 PeV scale1 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 ray production e+e- Pair production


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 Geant4Processes in Geant4 in-flight absorption Rayleigh scattering medium-boundary interactions

(reflection, refraction) Track of a photon entering a light concentrator CTF-Borexino


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


Hadronic physicsParameterised and data-driven models (1)

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

p elastic scattering on Hydrogen


Hadronic physicsParameterised and data-driven models (2)

Other models are completely new, such as stopping particles (- , K- ) neutron transport isotope production

NeutronsCourtesy of CMS

nuclear deexcitation

absorption

Stopping

MeV

Energy

All databases existing worldwide used in neutron transport

Brond, CENDL, EFF, ENDFB, JEF, JENDL, MENDL etc.


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


A sample from theory-driven models


Other components

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++


Sector Shielding

Analysis Tool

CAD tool

front-end

Delayed

radioactivity

General purpose

source particle module

INTEGRAL and other science missions

Instrument design purposesDose calculations

Particle source and spectrum

Geological surveys

Modules for space applications

Low-energy e.m. extensions


Fast simulation

Geant4 allows to perform full simulation and fast simulation in the same environment Geant4 parameterisation produces 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


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)


Documentation

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

http://cern.ch/geant4/geant4.html

Seminars and Training courses available


Conclusions

The software challengeThe 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 challengeThe functionality challenge a variety of requirements from many

application domains (HEP, space, medical etc.)

The physics challengeThe physics challenge transparency extended coverage of physics

processes across a wide energy range, with alternative models

The performance challengeThe performance challenge mandatory for large scale HEP

experiments and for other complex applications

The distributed software The distributed software developmentdevelopment

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 challengeThe user support challenge the user community is distributed

worldwide, operating in a variety of domains

Geant4 has successfully coped with a variety of challenges


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)

maria grazia pia, infn genova overview of the object oriented simulation toolkit maria grazia pia...

Documents

kinds of simulation

role of simulation

simulation application

validation of physics

alternative components

infn genova overview

infn genova egs4

potential physics output