Simulation capabilities and application results

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Simulation capabilities and application results
http//cern.ch/geant4/geant4.html

• Maria Grazia Pia
• INFN Genova
• on behalf of the Geant4 Collaboration

EPS-HEP 2001 Conference Budapest, 12-18 July 2001
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A rigorous approach to software engineering
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A wide domain of applications with a large user
community in many fields
HEP, astrophysics, nuclear physics, space
sciences, medical physics, radiation studies etc.

• Geant4 is a simulation Toolkit designed for a
  variety of applications
• It adopts rigorous software engineering
  methodologies and is based on OO technology
• It has been developed and is maintained by an
  international collaboration of gt 100 scientists
• RD44 Collaboration (1994-98)
• 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
• run, event and track management
• geometry and materials
• tracking
• detector response
• PDG-compliant particle management
• user interface
• visualisation
• persistency
• physics processes

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Software Engineering
plays a fundamental role in Geant4

• formally collected
• systematically updated
• PSS-05 standard

User Requirements
Software Process

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

• OOAD
• use of CASE tools

Object Oriented 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

Quality Assurance
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Geometry
Role detailed detector description and efficient
navigation
Multiple representations (Same abstract interface)

• 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 ISO STEP interface
Fields of variable non-uniformity and
differentiability
External tool for g3tog4 geometry conversion
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Guidelines for 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.
with attention to UR
Geant4 physics keeps evolving
facilitated by the OO technology
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Geant4 Physics

• 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

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

• Multiple scattering
• Bremsstrahlung
• Ionisation
• Annihilation
• Photoelectric effect
• Compton scattering
• Rayleigh effect
• g conversion
• ee- pair production
• Synchrotron radiation
• Transition radiation
• Cherenkov
• Refraction
• Reflection
• Absorption
• Scintillation
• Fluorescence
• Auger (in progress)

energy loss

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

Comparable to Geant3 already in the 1st a release
(1997) Further extensions (facilitated by the OO
technology)

• High energy extensions
• needed for LHC experiments, cosmic ray
  experiments
• Low energy extensions
• fundamental for space and medical applications,
  n experiments, antimatter
  spectroscopy etc.
• Alternative models for the same process

All obeying to the same abstract Process
interface ? transparent to tracking
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Standard e.m. processes
1 keV up to O(100 TeV)
Multiple scattering 6.56 MeV proton , 92.6 mm Si

• Multiple scattering
• new model (by L. Urbán)
• computes mean free path length and lateral
  displacement
• New energy loss algorithm
• optimises the generation of d rays near
  boundaries
• Variety of models for ionisation and energy loss
• including the PhotoAbsorption Interaction model
• Differential and Integral approach
• for ionisation, Bremsstrahlung, positron
  annihilation, energy loss and multiple scattering

J.Vincour and P.Bem Nucl.Instr.Meth. 148. (1978)
399
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Low energy e.m. extensions
shell effects
Fundamental for neutrino/dark matter experiments,
space and medical applications, antimatter
spectroscopy etc.
Bragg peak
e,? down to 250 eV (EGS4, ITS to 1 keV, Geant3
to 10 keV)
Hadron and ion models based on Ziegler and ICRU
data and parameterisations
Based on EPDL97, EEDL and EADL evaluated data
libraries
Barkas effect (charge dependence) models for
negative hadrons
Photon attenuation
ions
protons
antiprotons
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Muons
Optical photons

• 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)

• 1 keV up to 1000 PeV scale
• simulation of ultra-high energy and cosmic ray
  physics
• High energy extensions based on theoretical models

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Parameterised and data-driven hadronic 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
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Parameterised and data-driven hadronic models (2)

• Other models are completely new, such as

stopping particles ?- , K- (relevant for m/p
PID detectors)
Isotope production
neutrons

• All worldwide existing databases used in neutron
  transport
• Brond, CENDL, EFF, ENDFB, JEF, JENDL, MENDL etc.

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Theory-driven models
Complementary and alternative models

• Evaporation phase
• Low energy range, pre-equilibrium, O(100 MeV)
• Intermediate energy range, O(100 MeV) to O(5
  GeV), intra-nuclear transport
• High energy range, hadronic generator régime

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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, batchmacros,
  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

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Modules for space applications
Delayed radioactivity
General purpose source particle module
INTEGRAL and other science missions
Low-energy e.m. extensions
Particle source and spectrum
Geological surveys of asteroids
Sector Shielding Analysis Tool
CAD tool front-end
Instrument design purposes
Dose calculations
Courtesy of P. Nieminen, ESA
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Interface to external tools
Through abstract interfaces
? No dependence ? Minimize coupling of
components
Example AIDA Analysis Tools

• Similar approach
• graphics
• (G)UI
• persistency
• etc.

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BaBar
Courtesy of D. Wright for the BaBar Collaboration
Preliminary
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Example of integrated Fast/Full Simulation
application

• BaBar Object-oriented Geant4-based Unified
  Simulation (BOGUS)
• Integrated framework for Fast and Full simulation
• Fast simulation available for public use since
  February 1999
• Integrated in BaBar environment
• primary generators, reconstruction, OODB
  persistency
• parameters for materials and geometry shared with
  reconstruction applications

Exploits Geant4 parameterisation (new feature)
Courtesy of G. Cosmo for the BaBar Collaboration
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ATLAS
300 GeV muons 20 GeV pions
TRT Energy loss measured in ATLAS test beam
compared to Geant3 and Geant4 simulations (PAI
model)
Preliminary
Liquid Ar calorimeter Fcal energy resolution
Muon detector
Courtesy of D. Barberis for ATLAS Collaboration
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HARP with GEANT4
Courtesy of P. Arce for the HARP Collaboration
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T9 beam line
Preliminary

• Sophisticated geometry
• Very non-uniform strong magnetic field
• Primary target as a particle source

Crucial to have a precise absolute knowledge of
the particle rate incident onto HARP target
Beam profile and composition at the HARP target
Impossible to separate experimentally p from m in
the beam with the accuracy required
Courtesy of P. Arce for the HARP Collaboration
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GLAST (g-ray telescope)
Preliminary
Courtesy of F. Longo and R. Giannitrapani, GLAST
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Other astroparticle applications
Solar system explorations

• low E physics
• fluorescence
• radioactivity
• neutrons
• space modules
• etc..

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Technology transfer
anisotropy

• Medical applications of Geant4
• radiotherapy
• PET
• dosimetry
• etc.

Brachytherapy
Treatment planning
Courtesy National Inst. for Cancer Research,
Genova
Isodoses
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Conclusions

• Geant4 is a simulation Toolkit, providing
  advanced tools for all the domains of detector
  simulation
• Geant4 is characterized by a rigorous approach to
  software engineering
• Thanks to the OO technology, Geant4 is open to
  extension and evolution
• An abundant set of physics processes is
  available, often with a variety of complementary
  and alternative physics models
• Its areas of application span diverse fields HEP
  and nuclear physics, astrophysics and space
  sciences, medical physics, radiation studies etc.