A Linear Collider Physics List for Geant4 Simulations

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A Linear Collider Physics List for Geant4
Simulations

• Victoria Linear Collider Workshop
• 28-31 July 2004
• Dennis Wright (SLAC)

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Objectives

• Provide a standard Geant4 physics list to be
  used in study of LC detectors
• Make the list easy to use and understand
• Keep it up-to-date as new models become available
• Validate as test beam data becomes available
• Include it in LC Geant4 example (Makoto Asai)

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Physics List Design

• For simplicity
• Provide only one list everyone can use
• Specialized lists could be added later
• Avoid hadronic list libraries
• These are nice, but too general and somewhat
  involved
• Write out a long-hand physics list
• Derived from G4VModularPhysicsList
• Everything contained in 12 files
• Easy to see what processes/models are used and
  how they are invoked

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Physics List Contents (1)

• All applicable standard EM and decay processes
  (as available in Geant4 6.2)
• Hadron processes and models taken from the
  QGSP_BERT hadronic physics list
• For incident (p, K, p, n) energies of 20 GeV to
  100 TeV
• (QGS) Quark Gluon String PRE (Precompound)
  models
• For all others (L, S, anti-p, ...) with energies
  20 GeV to 100 TeV
• HEP (High Energy Parameterized model)
• For all particles with energies between 9.5 GeV
  to 20 GeV
• LEP (Low Energy Parameterized model)

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Physics List Contents (2)

• For incident p, p, n with energies lt 10 GeV
• Bertini cascade model
• For all others (K, anti-n, ...) with energies lt
  10 GeV
• LEP
• At rest processes for p- , K- absorption,
  anti-p, anti-n annihilation
• Neutron capture, neutron-induced fission
• Elastic hadron-nucleus scattering (same model for
  all hadrons)
• Added processes for light ions (d, t, 3He, a)
• Elastic scattering
• LEP model for inelastic (d, t, a)

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Justification of Model Choices20 GeV and Above

• Three models to choose from
• HEP works for all particles
• QGS, FTF work for p, K, p, n only
• Use testbeam data to decide
• e/p ratio from Atlas HEC prefers QGS, HEP
• No data yet to say if QGS is better than HEP
• Choose QGS because
• It is more thoroughly validated
• It is based more on physics than parameterization
• So use QGS for p, K, p, n, HEP for all others

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Fig.1

• F

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Fig. 2

• D

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Justification of Model ChoicesBelow 20 GeV

• Between 10 and 20 GeV, only one model available
  LEP
• Below 10 GeV, three models to choose from
• Low energy parameterized (LEP) for all
  particles
• Bertini cascade for p, p, n only
• Binary cascade for p, p, n only
• Pion production reactions clearly eliminate LEP
• Bertini and Binary equally good, Bertini 8x
  faster
• So LEP plus Bertini cascade required in list

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Fig. 3

• S

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Fig. 4

• W

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Plans

• Add gamma- and electro-nuclear processes/models
• Extend Bertini cascade to kaons
• Add hadronic interactions for light ions (to
  replace LEP)
• Validation gap 1 15 GeV
• Eagerly awaiting HARP publication
• Looking for other test beam data in this range

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Maintenance and Use

• Physics list will be maintained in FreeHEP CVS
• Anyone can get it
• cvs -d pserveranonymous_at_cvs.freehep.org/cvs/lc
  d LCPhys
• Better models, bug fixes will be included as
  available
• Questions, problems to
• dwright_at_slac.stanford.edu

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Geant4 Highlights at Release 6.2

• RunManager
• Now modularized, easier to embed in a framework
• Event
• Links between pre-assigned decay products and
  primary maintained
• User information can be attached to event in
  G4VUserEventInformation (also track, vertex,
  particle and region)
• Geometry
• First steps taken to abstract navigator -gt other,
  quite different steppers will soon be enabled
• New default values for tracking in EM field -gt
  improved accuracy
• Divisions (ala Geant3) introduced

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Geant4 Highlights at Release 6.2

• Visualization
• New HepRep XML driver for HepRep2
• New visualization commands
• Remove obsolete OPACS driver
• Environments
• MOMO Java tools now included (geometry and
  physics editors)
• Biasing
• Importance, weight-window methods available
• Co-works with scoring
• EM processes
• Example physics lists available

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Coming Highlights from Release 7.0

• Unknown particle class
• Propagated in a field, through materials
• Appears as a track/trajectory
• Will decay if and only if pre-assigned decay
  channel is defined for that track
• PDG compliance for particle numbers
• Geometry
• Mixing of placements and parameterized volumes
• Twisted trapezoid shape
• Reflection of parameterized volumes

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Coming Highlights from Release 7.0

• EM processes
• Performance analysis and optimization of showers
• Hadronic processes
• Revised physics lists based on new/updated models
• NLD1 example
• Demonstrates use of unknown particle, region
  user information, linking of primary particles,
  tracks, trajectories, hits
• Includes physics list previously discussed
• Currently available at http//www.slac.stanford.ed
  u/asai/NLD1/
• Will be extended example in release