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Slide1 l.jpg

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

The role of simulation l.jpg

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

The zoo l.jpg
The zoo








EGS4, EGS5, EGSnrc



Geant3, Geant4

Tripoli-3, Tripoli-3 A, Tripoli-4












...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

Integrated suites vs specialised codes l.jpg


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


a typical experiment covers many domains, not just one

domains are often inter-connected


the same environment provides all the functionality


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

The toolkit approach l.jpg
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

The geant approach l.jpg
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

Slide7 l.jpg

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


detector response

run, event and track management

PDG-compliant particle management


user interface


physics processes

It is also complemented by specific modules for space science applications

Geant4 collaboration l.jpg

Atlas, BaBar, CMS, HARP, LHCB applications


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

Software engineering l.jpg

Use of Standards applications

  • 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


Standards l.jpg

Units applications

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 VRMLfor graphics

  • CVSfor code management

  • C++as programminglanguage

  • STEP

    engineering and CAD systems

  • ODMG


Have you heard of the “incident” with NASA’s Mars Climate Orbiter ($125 million)?

Data libraries l.jpg
Data libraries applications

  • Systematic collection and evaluation of experimental data from many sources worldwide

  • Databases


  • 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 l.jpg

Platforms applications

DEC, HP, IMB-AIX, SUN, (SGI): native compilers, g++

Linux: g++

Windows-NT: Visual C++

Commercial software

ObjectStore STL (optional)

Free software


gmake, g++



OpenGL, X11, OpenInventor, DAWN, VRML...



it is possible to run in transient mode

in persistent mode use a HepDB interface, ODMG standard

What is needed to run Geant4

The kernel l.jpg

Run and event applications

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.


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

Geometry l.jpg

Multiple representations applications

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)


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 l.jpg
Things one can do with Geant4 geometry applications

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

A selection of geometry applications l.jpg

Chandra applications(NASA)

A selection of geometry applications

BaBar at SLAC

XMM-Newton (ESA)




Borexino at Gran Sasso Lab.

Physics l.jpg
Physics applications

  • 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 l.jpg

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

Processes l.jpg
Processes without changing other parts of the software

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

Electromagnetic physics l.jpg

multiple scattering without changing other parts of the software




photoelectric effect

Compton scattering

Rayleigh effect

g conversion

e+e- pair production

synchrotron radiation

transition radiation







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

Slide21 l.jpg

P without changing other parts of the softwarehoto 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

Muon processes l.jpg
Muon processes without changing other parts of the software

  • 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

Processes for optical photons l.jpg
Processes for optical photons without changing other parts of the software

  • 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

Hadronic physics l.jpg
Hadronic physics without changing other parts of the software

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 physics parameterised and data driven models 1 l.jpg

Based on experimental data without changing other parts of the software

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

Hadronic physics parameterised and data driven models 2 l.jpg

Other models are completely new, such as without changing other parts of the software

stopping particles (- , K- )

neutron transport

isotope production

Stopping p



Courtesy of CMS

nuclear deexcitation



Hadronic physicsParameterised and data-driven models (2)

  • Alldatabases existing worldwide used in neutron transport


Hadronic physics theoretical models l.jpg
Hadronic physics without changing other parts of the softwareTheoretical 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 l.jpg
A sample from theory-driven models without changing other parts of the software

Other components l.jpg

Materials without changing other parts of the software

elements, isotopes, compounds, chemical formulae


all PDG data

and more, for specific Geant4 use, like ions

Hits & Digi

to describe detector response


possibility to run in transient or persistent mode

no dependence on any specific persistency model

persistency handled through abstract interfaces to ODBMS


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

Modules for space applications l.jpg
Modules for space applications without changing other parts of the software

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

Fast simulation l.jpg
Fast simulation without changing other parts of the software

  • 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

Performance l.jpg
Performance without changing other parts of the software

  • 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 l.jpg

User Documentation without changing other parts of the software

Introduction to Geant4

Installation Guide

Application Developer Guide

Toolkit Developer Guide

Software Reference Manual

Physics Reference Manual


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


Publication and Results web page


Low Energy e.m. Physics




Seminars and Training courses available

Conclusions l.jpg

The software challenge without changing other parts of the software

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


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


Geant4 has successfully coped with a variety of challenges

Geant4 review l.jpg
Geant4 review without changing other parts of the software

  • 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)