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Geant4—a simulation toolkit

Abstract: G eant 4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics.
Topics: Applied physics (54%)

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Nuclear Instruments and Methods in Physics Research A 506 (2003) 250303
Gea nt4—a simulation toolkit
S. Agostinelli
, J. Allison
*, K. Amako
, J. Apostolakis
, H. Araujo
P. Arce
, M. Asai
, D. Axen
, S. Banerjee
, G. Barrand
, F. Behner
L. Bellagamba
, J. Boudreau
, L. Broglia
, A. Brunengo
, H. Burkhardt
S. Chauvie
, J. Chuma
, R. Chytracek
, G. Cooperman
, G. Cosmo
P. Degtyarenko
, A. Dell’Acqua
, G. Depaola
, D. Dietrich
, R. Enami
A. Feliciello
, C. Ferguson
, H. Fesefeldt
, G. Folger
, F. Foppiano
A. Forti
, S. Garelli
, S. Giani
, R. Giannitrapani
, D. Gibin
, J.J. G
, I. Gonz
, G. Gracia Abril
, G. Greeniaus
, W. Greiner
V. Grichine
, A. Grossheim
, S. Guatelli
, P. Gumplinger
, R. Hamatsu
K. Hashimoto
, H. Hasui
, A. Heikkinen
, A. Howard
, V. Ivanchenko
A. Johnson
, F.W. Jones
, J. Kallenbach
, N. Kanaya
, M. Kawabata
Y. Kawabata
, M. Kawaguti
, S. Kelner
, P. Kent
, A. Kimura
T. Kodama
, R. Kokoulin
, M. Kossov
, H. Kurashige
, E. Lamanna
T. Lamp
, V. Lara
, V. Lefebure
, F. Lei
, M. Liendl
W. Lockman
, F. Longo
, S. Magni
, M. Maire
, E. Medernach
K. Minamimoto
, P. Mora de Freitas
, Y. Morita
, K. Murakami
M. Nagamatu
, R. Nartallo
, P. Nieminen
, T. Nishimura
, K. Ohtsubo
M. Okamura
, S. O’Neale
, Y. Oohata
, K. Paech
, J. Perl
, A. Pfeiffer
M.G. Pia
, F. Ranjard
, A. Rybin
, S. Sadilov
, E. Di Salvo
, G. Santin
T. Sasaki
, N. Savvas
, Y. Sawada
, S. Scherer
, S. Sei
, V. Sirotenko
D. Smith
, N. Starkov
, H. Stoecker
, J. Sulkimo
, M. Takahata
, S. Tanaka
E. Tcherniaev
, E. Safai Tehrani
, M. Tropeano
, P. Truscott
, H. Uno
L. Urban
, P. Urban
, M. Verderi
, A. Walkden
, W. Wander
, H. Weber
J.P. Wellisch
, T. Wenaus
, D.C. Williams
, D. Wright
, T. Yamada
H. Yoshida
, D. Zschiesche
European Organization for Nuclear Research (CERN) Switzerland
European Space Agency (ESA), ESTEC, The Netherlands
Istituto Nazionale di Fisica Nucleare (INFN), Italy
Jefferson Lab, USA
KEK, Japan
*Corresponding author. Tel.: +44-161-275-4179; fax: +44-161-273-5867.
E-mail address: (J. Allison).
0168-9002/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.

Lebedev Institute, Russia
Stanford Linear Accelerator Center (SLAC), USA
TRIUMF, Canada
ATLAS Collaboration, CERN, Switzerland
BaBar Collaboration, USA
Borexino Collaboration, Italy
CMS Collaboration, CERN, Switzerland
HARP Collaboration, CERN, Switzerland
LHCb Collaboration, CERN, Switzerland
RWTH, Aachen, Germany
University of Alberta, Canada
ALICE Collaboration, CERN, Switzerland
University of Bath, UK
University of Birmingham, UK
University of British Columbia, Canada
Brookhaven National Laboratory, USA
Kfki, Budapest, Hungary
a della Calabria and INFN, Italy
University of Cordoba, Spain
University of Dortmund, Germany
Fukui University, Japan
IST Natl. Inst. for Cancer Research of Genova, Italy
INFN Genova, Italy
a di Genova, Italy
Inst. f
ur Theoretische Physik, Johann Wolfgang Goethe Universit
at, Frankfurt, Germany
HERMES Collaboration, DESY, Germany
Helsinki Institute of Physics (HIP), Finland
Hiroshima Institute of Technology, Japan
Imperial College of Science, Technology and Medicine, London, UK
IHEP Protvino, Russia
North Illinois University, USA
Kobe University, Japan
IN2P3/LAL, Orsay, France
IN2P3/LAPP, Annecy, France
IN2P3/LLR, Palaiseau, France
EPFL, Lausanne, Switzerland
Lyon University, France
Department of Physics and Astronomy, The University of Manchester, UK
MEPhI, Moscow, Russia
INFN, Milan, Italy
Naruto University of Education, Japan
Niigata University, Japan
Northeastern University, USA
Budker Institute for Nuclear Physics, Novosibirsk, Russia
Osaka Institute of Technology, Japan
a di Padova, Italy
University of Pittsburg, USA
QinetiQ, UK
Ritsumeikan University, Japan
University of Southampton, UK
TIFR, Mumbai, India
INFN, Torino, Italy
Tokyo Metropolitan University, Japan
S. Agostinelli et al. / Nuclear Instruments and Methods in Physics Research A 506 (2003) 250303 251

a di Torino, Italy
a di Trieste and INFN Trieste, Italy
UCSC, Santa Cruz, USA
a di Udine and INFN Udine, Italy
University of Valencia, Spain
IFIC Instituto de Fisica Corpuscular de Valencia, Spain
Vienna University of Technology, Austria
Geant4 Collaboration
Received 9 August 2002; received in revised form 11 March 2003; accepted 14 March 2003
Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of
functionality including tracking, geometry, physics models and hits. The physics processes offered cover a
comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived
particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in
others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle
complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit
is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting
software engineering and object-oriented technology and implemented in the C++ programming language.
It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical
r 2003 Elsevier Science B.V. All rights reserved.
PACS: 07.05.Tp; 13; 23
Keywords: Simulation; Particle interactions; Geometrical modelling; Software engineering; Object-oriented technology; Distributed
software development
1. Introduction
Modern particle and nuclear physics experi-
ments pose enormous challenges in the creation of
complex yet robust software frameworks and
applications. Of particular importance is the
ever-increasing demand for large-scale, accurate
and comprehensive simulations of the particle
detectors used in these experiments. The demand
is driven by the escalating size, complexity, and
sensitivity of the detectors and fueled by the
availability of moderate-cost, high-capacity com-
puter systems on which larger and more complex
simulations become possible. Similar considera-
tions arise in other disciplines, such as: radiation
physics, space science, nuclear medicine and, in
fact, any area where particle interactions in matter
play a role.
In response to this, a new object-oriented
simulation toolkit, Gea nt4, has been developed.
The toolkit provides a diverse, wide-ranging, yet
cohesive set of software components which can be
employed in a variety of settings. These range from
simple one-off studies of basic phenomena and
geometries to full-scale detector simulations for
experiments at the Large Hadron Collider and
other facilities.
In defining and implementing the software
components, all aspects of the simulation process
have been included: the geometry of the system,
the materials involved, the fundamental particles
of interest, the generation of primary particles of
events, the tracking of particles through materials
and external electromagnetic fields, the physics
processes governing particle interactions, the
response of sensitive detector components, the
S. Agostinelli et al. / Nuclear Instruments and Methods in Physics Research A 506 (2003) 250303252

generation of event data, the storage of events and
tracks, the visualisation of the detector and
particle trajectories, and the capture for subse-
quent analysis of simulation data at different levels
of detail and refinement.
Early in the design phase of the project, it was
recognised that while many users would incorpo-
rate the Geant4 tools within their own computa-
tional framework, others would want the
capability of easily constructing stand-alone ap-
plications which carry them from the initial
problem definition right through to the production
of results and graphics for publication. To this
end, the toolkit includes built-in steering routines
and command interpreters which operate at the
problem setup, run, event, particle transportation,
visualisation, and analysis levels, allowing all parts
of the toolkit to work in concert.
At the heart of this software system is an
abundant set of physics models to handle the
interactions of particles with matter across a very
wide energy range. Data and expertise have been
drawn from many sources around the world and in
this respect Geant4 acts as a repository that
incorporates a large part of all that is known about
particle interactions; moreover it continues to be
refined, expanded and developed. A serious
limitation of many previous simulation systems
was the difficulty of adding new or variant physics
models; development became difficult due to the
increasing size, complexity and interdependency of
the procedure-based code. In contrast, object-
oriented methods have allowed us effectively to
manage complexity and limit dependencies by
defining a uniform interface and common organi-
sational principles for all physics models. Within
this framework, the functionality of models can be
more easily seen and understood, and the creation
and addition of new models is a well-defined
procedure that entails little or no modification to
the existing code.
Geant4 was designed and developed by an
international collaboration, formed by individuals
from a number of cooperating institutes, HEP
experiments, and universities. It builds on the
accumulated experience of many contributors to
the field of Monte Carlo simulation of physics
detectors and physical processes. While geogra-
phically distributed software development and
large-scale object-oriented systems are no longer
a novelty, we consider that the Geant4 Collabora-
tion, in terms of the size and scope of the code and
the number of contributors, represents one of the
largest and most ambitious projects of this kind. It
has demonstrated that rigorous software engineer-
ing practices and object-oriented methods can be
profitably applied to the production of a coherent
and maintainable software product, even with the
fast-changing and open-ended requirements pre-
sented by physics research.
In the following sections we present a detailed
overview of Geant4 and its features and capabil-
ities, including the design and implementation of
the various categories of physics models. Many
new physics models have been developed, and
others have been refined or extended. They have
been created to support a growing range of
applications for the software, including particle,
nuclear, medical, accelerator and space physics.
The code and documentation, as well as tutorials
and examples, are available from our Web site [1].
1.1. History of Geant4
The origin of Geant4 development can be
traced back to two studies done independently at
CERN and KEK in 1993 [2]. Both groups sought
to investigate how modern computing techniques
could be applied to improve what was offered by
the existing GEANT3 program [3], which was a
benchmark and source of ideas and valuable
experience. These two activities merged and a
proposal was submitted to the CERN Detector
Research and Development Committee (DRDC)
[4] to construct a simulation program based on
object-oriented technology. The resulting project
was RD44, a worldwide collaboration that grew to
include the efforts of 100 scientists and engineers,
drawn from more than 10 experiments in Europe,
Russia, Japan, Canada and the United States.
The design choices faced by RD44 and the
decisions arrived at are described in later sections,
but key to its success was a careful design adapting
object-oriented methodology and an early decision
to use the practical C++ language.
S. Agostinelli et al. / Nuclear Instruments and Methods in Physics Research A 506 (2003) 250303 253

The R&D phase was completed in December
1998 [1] with the delivery of the first production
release. Subsequently the Geant4 Collaboration
was established in January 1999 to continue the
development and refinement of the toolkit, and to
provide maintenance and user support.
1.2. Organisation of the collaboration
A Memorandum of Understanding (MoU) [5]
signed by all participating parties governs the
formal collaboration. It is subject to tacit renewal
every 2 years and sets out a collaboration structure
composed of a Collaboration Board (CB), a
Technical Steering Board (TSB) and several work-
ing groups. The MoU also defines the way in
which collaboration resources—money, man-
power, expertise, and key roles and activities (such
as program librarian and documentation man-
ager)—are measured in Contribution Units (CU),
and it further delineates how the boards are
constituted depending on the CU count for each
signatory. Participating groups include experimen-
tal teams and collaborations, laboratories and
national institutes.
It is the CB’s mandate to manage these
resources and to monitor the agreed responsibil-
ities among the affiliates. This body is also charged
with the evolution of the MoU. The TSB, on the
other hand, is the forum where technical matters,
like software engineering details and physics model
implementation issues, are discussed and decided
and where priorities are given to user requests. Its
primary tasks are the supervision of the produc-
tion service and the user support and the over-
seeing of ongoing further development of the
program. The TSB is chaired by the spokesperson
of the Collaboration, who is appointed by and
reports to the CB. The spokesperson is (re)elected
every two years.
Every domain of the Geant4 software that
corresponds to a releasable component (library) is
individually managed by a working group of
experts. In addition, there is a working group for
each of the activities of testing and quality
assurance, software management and documenta-
tion management. A coordinator who is selected
by the TSB heads each group. There is also an
overall release coordinator. This clean overall
problem decomposition makes the distributed
software design and development possible in a
worldwide collaboration. Every group can work in
parallel, allowing an optimal use of manpower and
1.3. User support, documentation and source code
The Collaboration provides documentation and
user support for the toolkit. The support model is
described in more detail in Section 3.6.
Documentation [6] includes installation, user
and reference guides, and a range of training kits
(see also Section 1.4). It is intended to cover the
need of the beginner through to the expert user
who wishes to expand the capabilities of Gea nt4.
User support covers help with problems relating
to the code, consultation on using the toolkit and
responding to enhancement requests. A user may
also expect assistance in investigating anomalous
A Web-based reporting system and a list of
frequently asked questions (FAQs) are available
on the Geant4. Web site [1]. The Collaboration
also runs a Web-based user forum [7], with sub-
forums according to areas of different interest.
Regular releases of the source code and doc-
umentation are freely available on the Web.
1.4. Examples and training kits
The toolkit includes examples at three levels:
Novice: for understanding basic functionalities;
Extended: focused on specific domains of
application (they may also need additional
third party libraries);
Advanced: full programs created to utilise
Geant4 in HEP experiments, and for space
and medical applications.
They are intended to develop the user’s under-
standing in many areas. Initial emphasis is on the
classes describing the user’s setup, which are
required by the toolkit. These classes are explained
in Section 2.4.
Geant4 also provides a training kit. It consists
of a modular set of units, each covering a specific
S. Agostinelli et al. / Nuclear Instruments and Methods in Physics Research A 506 (2003) 250303254

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Journal ArticleDOI
01 Jul 1983-Physics Reports
Abstract: While muchhasbeenlearnedrecentlyaboutquark andgluon interactionsin theframeworkof perturbativeQuantumChromodynamics,the relationbetweencalculatedpartonpropertiesandobservedhadrondensitiesinvolves modelswhere dynamicsandjet empincal ruleshaveto be combined.Thepurposeof this article is to describea presentlysuccessful approachwhich is basedon a cascadejet model usingStringdynamics.It can readily lead to Monte Carlo jet programmesof greatuse when analyzingdata. Production processesin an iterative cascadeapproach,with tunneling in a constantforce field, arereviewed. Expecteddifferencesbetweenquark and gluon jets are discussed.Low transversemomentum phenomenaare alsoreviewed with emphasison hyperon polarization. In so far as this approachusesa fragmentationschemebasedon String dynamics,it wasdeemedappropriateto alsoincludeunderthesamecovera specialreport on theClassicaltheoryof relativisticStrings,seenasthe classicallimit of theDual Resonancemodel. TheEquationsof motion and interactionamongstringsarepresented. Single ordersfor this issue PHYSICSREPOR1’S(Review Sectionof PhysicsLetters)97, Nos.2 & 3 (1983)31—171. Copies of this issue may be obtainedat the price givenbelow. All ordersshouldbe sentdirectly to the Publisher.Ordersmust be accompaniedby check. Single issuepriceDfl. 79.00, postageincluded. 34 B. Andersson et a!., Patton fragmentation and siring dynamics testsof the theory,in particularof the perturbativeQCD structure,containse.g.nonscalingdeviations from the partonmodel. There are at this point already some difficulties becauseit is well-known that any finite energy hadronicdistributionwill containnonscalingcontributions,sometimesto an evenlargerdegreethanthe inherent scale breaking effects of the theory. Further the pencilsharpenergyand momentumdistributions from the single partonsareessentiallydistorted, widenedin transversedirectionsandeven the basicquantumnumberslike chargeandstrangeness etc.seemto havebeentransportedsometimes ratherfar away in longitudinal rapidity space.It has thereforebecomeincreasinglyobvious over the yearsthat in order to compareexperimentto basictheory,it is necessaryto havereliabledescriptionsof the transferfrom the partonicstageto the hadronicone,i.e. to haveconsistentmodelsfor the process of partonfragmentation. Suchmodelsmayon the onehandbe lookedupon solely as phenomenological parametrizationsand rulesof thumb in order to obtain a translationfrom onelanguageto another.As such theyare useful for analysis of experiment as well as for the planning. On the other hand one may as always in connectionwith phenomenologytry to obtain a dynamicalframeworkthat servesas a motivation anda generalizingprinciple for theconstructions. It shouldbekept in mind, however,that thereareno easilyavailablemeasuresof the successof such a venture.As Bacontold us a long time ago,it is actuallyonly possibleto learnthat oneis wrong by a comparisonbetweenmodel calculationsand experimentalfindings. If the predictionagreesthereis no reassurancethat one is evenworking in the right basicdirection (althoughthereis evidentlya possible reasonto feelsomeconfidence!). A modestmeasureof successwould be a demandthat the numberof phenomenological parameters andthe variation in size of their valuesare nonincreasingfunctionsof time as well as the numberof independent experimentalfindings. It is alsoof evidentinterestthat thesamebasicschemeis applicable in different contextssuch as different partonic processesand different parts of phase-space. Several schemeswith a more or less profound theoreticalfoundationhavebeensuggestedbut we will in this review be concernedonly with iterative cascadejet modelsbasedupon string dynamics.The present experiencefrom thesemodelsshowsthat at leastthe above-mentionedcriteriafor successarefulfilled. We will in this reviewmostlydiscussa possibledynamicalframeworkbehindthe modelsandwe will only usecomparisonsto datain order to demonstratemattersof principle.One of the nice featuresof the models is their stochasticstructurewhich readily lends itself to an implementationin terms of computergeneration.Severalsuch MonteCarlojet programsareavailable[21for the interestedreader to makemuchmore detailedcomparisons. Our approachwill primarily be of a semi-classicalnature,i.e. we will at most placesmakeuseof a classicaldynamicalframeworkfor our considerations. We will, however,at all necessaryplacespoint to the basicquantummechanicalconstraints. It is well-known that by meansof a careful choice of dynamicalvariablesit is often possibleto circumvent such constraints.As an example we note that it is in general not possible to give independentvaluesto canonicallyconjugatevariablessuch as momentum(p) andposition(x) dueto Heisenberg’suncertaintyprinciple:

1,890 citations

01 Jan 1994-
TL;DR: The Capability Maturity Model for Software and the Evolution of the CMM: BackGROUND, CONCEPTS, STRUCTURES and USAGE are explained.
Abstract: I. THE CAPABILITY MATURITY MODEL FOR SOFTWARE: BACKGROUND, CONCEPTS, STRUCTURES AND USAGE. 1. Introducing Software Process Maturity. The Evolution of the CMM. Immature versus Mature Software Organizations. Fundamental Concepts Underlying Process Maturity. Total Quality Management and the CMM. Customer Satisfaction. Benefits and Risks of Model-Based Improvement. 2. The Software Process Maturity Framework. Behavioral Characterization of the Maturity Levels. Skipping Maturity Levels. Visibility into the Software Process. Prediction of Performance. 3. The Structure of the Capability Maturity Model. Internal Structure of the Maturity Levels . Maturity Levels. Key Process Areas. Key Practices. Common Features. 4. Interpreting the CMM. Interpreting the Key Practices. The Key Process Area Template. Interpreting the Common Features. Organizational Structure and Roles. Understanding Software Process Definition. The Evolution of Processes. Applying Professional Judgment. 5. Using the CMM. A CMM-Based Appraisal Method. Process Assessments and Capability Evaluation. Software Process Improvement. Using the CMM in Context. 6. A High-Maturity Example: Space Shuttle Onboard Software. Introduction. Background. Approaches to Process Improvement. Overall Lessons. II. THE KEY PRACTICES OF THE CAPABILITY MATURITY MODEL FOR SOFTWARE. 7. The Key Areas for Level 2: Repeatable. Requirements Management. Software Project Planning. Software Project Tracking and Oversight. Software Subcontract Management. Software Quality Assurance. Software Configuration Management. 8. The Key Process Areas for Level 3: Defined. Organization Process Focus. Organization Process Definition. Training Program. Integrated Software Management. Software Product Engineering. Intergroup Coordination. Peer Reviews. 9. The Key Process Areas for Level 4: Managed. Quantitative Process Management. Software Quality Management. 10. The Key Process Areas for Level 5:Optimizing. Defect Prevention. Technology Change Management. Process Change Management. Appendix A: References. Appendix B: Acronyms. Appendix C: Glossary. Appendix D: Abridged Version of the Key Practices. Appendix E: Mapping the Key Practices to Goals. Appendix F: Comparing ISO 9001 and the CMM. Appendix G: An Overview of ISO's SPICE Project. Appendix H: Change History of the CMM. Appendix I: Change Request Form. Index. 0201546647T04062001

1,393 citations

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