Electromagnetic Physics

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Electromagnetic Physics

• Maria Grazia Pia
• CERN/IT and INFN Genova
• S. Chauvie, V. Grichine, P. Gumplinger, V.
  Ivanchenko, R. Kokoulin,
• S. Magni, M. Maire, P. Nieminen, M.G. Pia, A.
  Rybin, L. Urban

MC2000 Conference, Lisbon, 20-23 October 2000
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Highlights
A wide domain of applications with a large user
community in many fields
CMS at LHC, CERN
HEP, astrophysics, nuclear physics, space
sciences, medical physics, radiation studies etc.
X ray telescope
XMM
Borexino at Gran Sasso Laboratory
A rigorous approach to software engineering
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• Geant4 is a simulation Toolkit designed for a
  variety of applications
• It has been developed and is maintained by an
  international collaboration of gt 100 scientists
• RD44 Collaboration
• Geant4 Collaboration
• The code is publicly distributed from the WWW,
  together with ample documentation

• 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

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Software Engineering
Geant4 architecture
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

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
Use of Standards

• de jure and de facto

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Features of 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
• ee- pair production
• photoelectric effect
• Compton scattering
• Rayleigh effect
• g conversion
• synchrotron radiation
• transition radiation
• Cherenkov
• refraction
• reflection
• absorption
• scintillation
• fluorescence
• Auger (in progress)

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

energy loss
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OO design
Top level class diagram of electromagnetic physics
Alternative models, obeying the same abstract
interface, are provided for the same physics
interaction
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Standard electromagnetic processes
Shower profile, 1 GeV e- in water

• Photons
• Compton scattering
• g conversion
• photoelectric effect
• Electrons and positrons
• Bremsstrahlung
• ionisation
• continuous energy loss from Bremsstrahlung and
  ionisation
• d ray production
• positron annihilation
• synchrotron radiation
• Charged hadrons

JH Crannel - Phys. Rev. 184-2 August69
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Features of Standard e.m. processes
Multiple scattering 6.56 MeV proton , 92.6 mm Si

• Multiple scattering
• new model
• computes mean free path length and lateral
  displacement
• Super energy loss
• 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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Photo Absorption Ionisation Model
Ionisation energy loss produced by charged
particles in thin layers of absorbers
3 GeV/c p in 1.5 cm ArCH4
5 GeV/c p in 20.5 mm Si

• Ionisation energy loss distribution produced by
  pions, PAI model

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Low energy extensions e-, g
250 eV up to 100 GeV

• Based on EPDL97, EEDL and EADL evaluated data
  libraries
• cross sections
• sampling of the final state
• Photoelectric effect
• Compton scattering
• Rayleigh scattering
• Bremsstrahlung
• Ionisation
• Fluorescence

Photon transmission on 1 mm Al
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Low energy extensions hadrons and ions
Various models, depending on the energy range
and the charge

• E gt 2 MeV ? Bethe-Bloch
• 1 keV lt E lt 2 MeV ? parameterisations
• Ziegler 1977, 1985
• ICRU 1993
• corrections due to chemical formulae of materials
• nuclear stopping power
• E lt 1 keV ? free electron gas model
• Barkas effect taken into account down to 50 keV
• quantum harmonic oscillator model

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water

• Photon attenuation coefficient
• Comparison with NIST data
• Geant4
• Standard electromagnetic package
• and
• Low Energy extensions

Fe
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Muon processes

• Validity range
• 1 keV up to 1000 PeV scale
• ?simulation of ultra-high energy and cosmic ray
  physics
• High energy extensions based on theoretical
  models
• Bremsstrahlung
• Ionisation and d ray production
• ee- Pair production

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

Track of a photon entering a light concentrator
CTF-Borexino
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Openness to evolution

• 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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User support

• User Support is a key feature of Geant4
• Users (experiments, laboratories, institutes) are
  members of the collaboration itself
• User Requirements are formally collected and
  regularly updated
• Extensive documentation available from the web (5
  manuals)
• A Geant4 Training Programme in preparation
• User Support through a web interface for
  code-related problem reports
• User Support through human interface for
  consultancy, investigation of anomalous results
  etc.
• A distributed model of User Support
• a large number of experts performs the support on
  the domain of their competence
• The close relationship with user communities and
  their feedback is very valuable to Geant4

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Geant4 electromagnetic physics Working Groups

• M. Maire (LAPP)
• P. Nieminen (ESA)
• M.G. Pia (INFN Genova)
• S. Agostinelli - (IST Genova)
• P. Andreo (Karolinska Inst.)
• D. Belkic (Karolinska Inst.)
• A. Brahme (Karolinska Inst.)
• A. Carlsson (Karolinska Inst.)
• G. Cabras (INFN Udine)
• S. Chauvie (INFN Torino)
• G. Depaola (Univ. Cordova)
• R. Cirami (INFN Trieste)
• E. Daly (ESA)
• A. De Angelis (INFN Udine)
• G. Fedel (INFN Trieste)
• J.M. Fernandez Varea (Univ. Barcelona)
• S. Garelli (IST Genova)
• R. Giannitrapani (INFN Udine)
• V. Grichine (LPI Moscow)

• V. Ivanchenko (Budker Institute )
• R. Kokouline (MEPhI, Moscow)
• E. Lamanna (INFN Cosenza)
• S. Larsson (Karolinska Inst.)
• R. Lewensohn (Karolinska Inst.)
• B.K. Lind (Karolinska Inst.)
• J. Lof (Karolinska Inst.)
• F. Longo (INFN Trieste)
• B. De Lotto (INFN Udine)
• F. Marchetto (INFN Torino)
• E. Milotti (INFN Udine)
• R. Nartallo (ESA)
• G. Nicco (Univ. Torino)
• B. Nilsson (Karolinska Inst.)
• V. Rolando (Univ. Piemonte Orient.)
• A. Rybin (IHEP Protvino)
• G. Santin (INFN Trieste)
• U. Skoglund (Karolinska Inst.)
• A. Solano (INFN Torino)

Standard e.m. Physics
Low Energy e.m. Physics
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Conclusions

• Geant4 is a simulation Toolkit, providing
  advanced tools for all the domains of detector
  simulation
• Its areas of application span diverse domains
  HEP and nuclear physics, astrophysics and space
  sciences, medical physics, radiation studies etc.
• Geant4 is characterized by a rigorous approach to
  software engineering
• Geant4 electromagnetic physics covers a wide
  energy range of interactions of electrons and
  positrons, photons, muons, charged hadrons and
  ions
• An abundant set of electromagnetic physics
  processes is available, often with a variety of
  complementary and alternative physics models
• Low and high energy extensions have opened new
  domains of applications
• Thanks to the OO technology, Geant4 is open to
  extension and evolution

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Related presentations at this conference

• P. Nieminen Space applications of the Geant4
  Toolkit
• S. Chauvie Medical applications of the Geant4
  Toolkit
• V. Grichine Fast Simulation of X-ray Transition
  Radiation in the Geant4 Toolkit