Geant4: an update

1
Geant4 an update

• Makoto Asai, SLAC
• On behalf of
• the Geant4 collaboration
• and the SLAC Geant4 team

21 May 2003 LCSim workshop _at_ SLAC
2
Outline

• Most recent release
• Geant4 version 5.1 (Apr. 30, 2003)
• Patch-01 (May 19, 2003)
• Physics highlights
• New capabilities
• Some of the new Developments
• User support
• SLAC Geant4 team

3
Physics Development Highlights

• Geant4 releases Dec 2001-today included
• New theoretical hadronic models
• CHIPS for g-Nucleus, p capture, ..
• Cascade models Bertini (HETC) and Binary
• Details to be given by D.Wright
• New EM processes
• g to m pair
• new TR models
• Numerous physics improvements
• Including, for example
• Charge state for recoils
• Improved X-sections for e-Nuclear, with hard
  scattering

4
Multiple scattering

• Examples of comparisons
• 15.7 MeV e-
• on gold foil
• Modelling comparisons
• L. Urban

Angle (deg)
5
Significant developments in EM (std) in 2002

• Multiple scattering (L. Urban)
• Ultra relativistic energies (H. Burkardt, S.
  Kelner, R. Kokoulin)
• Ionization for Generic Ions (V. Ivanchenko)
• Models of Transition radiation detectors (V.
  Grichine)
• Redesign of few processes prototype model
  approach for Ionization and Bremsstrahlung (V.
  Ivanchenko)

6
Comparison projects

• Joint efforts for comparing Geant4 with
  experiment test-beam data.
• Results of EM comparisons 2000-2002.
• Hadronic comparisons 2002-ongoing.
• Collaboration with experiments
• ATLAS (projects with data of test beams of 4
  calorimeters)
• BaBar (with experiment data for tracker, drift
  chamber)
• Many results have been presented (by the
  experiments) at conferences workshops eg Calor
  2002.
• Presentations at quarterly LHC experiment-Geant4
  physics comparisons meetings, eg 4th March 2003.

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Tailored Physics lists

• Created and distribute educated guess physics
  lists
• That correspond to the major use cases of Geant4
  involving hadronic physics,
• to use directly, and as a starting point for
  users to modify,
• facilitate the specialization of those parts of
  hadronic physics lists that vary between use
  cases.
• First released in September 2002
• Using physics models of Geant4 4.1.
• Revised with experience of comparisons with data
• Latest
• updated with physics models of Geant4 5.0 in
  March 2003
• Find them on the G4 hadronic physics web pages
  http//cmsdoc.cern.ch/hpw/GHAD/HomePage

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Use cases of Physics Lists

• Calorimetry
• Tracker detectors
• Average HEP detector
• High energy physics calorimetry.
• High energy physics trackers.
• 'Average' HEP collider detector
• Low energy dosimetric applicationswith neutrons
• low energy nucleon penetration shielding
• linear collider neutron fluxes
• high energy penetration shielding

• medical and other life-saving neutron
  applications
• low energy dosimetric applications
• high energy production targets
• e.g. 400GeV protons on C or Be
• medium energy production targets
• e.g. 15-50 GeV p on light targets
• LHC neutron fluxes
• Air shower applications
• low background experiments

Contributors http//cern.ch/geant4/organisation/
working_groups.htmlwg.Had
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Resolution

• Original (org) results from Calor 2002
  presentation,
• (March 2002).
• Open symbols from additional physics lists JPW,
  May 2002, using geant4 4.0-patch2
• (released end Feb 2002).

Status of May 2002
Thanks to Atlas HEC and J.P. Wellisch
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BaBar

• Geant4 based simulation since 2001 production.
• More than 109 events (through Oct 2002)
• Used Geant4 3.1fixes, own transport.

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Improvements in Geometry

• Reflection of volume hierarchies
• Eg to create endcap geometry
• Improved voxelisation for performant navigation
• 3-D for parameterized volumes
• Now equal performance to placed volume
• Option to avoid voxelising some volumes
• Illegal geometries detected rejected
• E.g. incompatible daughters (placed
  parameterised)
• XML binding GDML 1.0 released
• Specification
• Implementation
• Refinements currently on hold.

I Hrivnacova G Cosmo V Grichine
G Cosmo
R Chytracek
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Debugging geometries

• It is easy to create overlapping volumes
• a volume that protrudes from its mother,
• 2 volumes that intersect in common mother
• During tracking Geant4 does not check for
  malformed geometries
• The problem of detecting significant overlaps
  is now addressed by
• DAVID that intersects volumes directly
• Uses graphical representations
• By S. Tanaka, released circa 1997
• New built-in run-time commands to run
  verification tests by its own navigation
• Using solids and a grid of rays
• Created DC Williams released in 4.0
• New example with full tracking / navigation
• Uses the full hierarchy the Navigator
• Created by M Liendl released in 5.0

Thanks to S. Tanaka
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Variance reduction

• Geant4 has had an event biasing option for the
  transportation of low energy neutrons.
• The formulae are derived from MARS95.
• New, redesigned and improved, implementation in
  Geant4 4.1.
• It was possible to use other methods, but only in
  user code.
• Now new general purpose built-in methods have
  been created.
• Importance biasing
• Splitting/Russian roulette (first released in G4
  4.1, June 2002).
• Importance values can be associated to a mass
  geometry or to a ghost geometry.
• Varied options in driving MC history and
  scoring tallies
• No changes to the kernel were required, due to
  the flexibility of the toolkit.

M Dressel
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CPU Performance

• Our simple benchmarks
• Geometry faster, EM shower setups competitive
• Performance in experimental setups (with Geant4
  releases 2 and 3) was comparable to Geant3
• few counterexamples, including BTeV ECAL.
• New performance issue arose with Geant4 4.0
• and were addressed (in the patches release 4.1)
• Difficult cases remain, including
• Some setups of EM showers and field propagation,
  factor 2x
• Collecting a set of benchmarks
• To follow computing performance regularly
• To be included in SPEC 2004 benchmark
• Goal is that Geant4 is at least as fast as Geant3
  in almost all cases
• When its power is used.

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Visualization
DAWN renderer Thanks to S. Tanaka

• Geometry, hits
• New
• DTREE hierarchy display
• HEPREP and Wired driver
• Other Current Drivers
• OpenGL
• Popular, hardware speed
• VRML
• Portable, lower detail
• DAWN renderer
• High quality Postscript
• Also from others, eg
• IGUANA (for CMS simulation)

Iguana, thanks to L.Tuura, I. Osborne
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Cuts per region

• Full release in Geant4 5.1 (end April)
• Comparable run-time performance
• Geant4 has had a unique production threshold
  (cut) expressed in length (range of secondary).
• For all volumes
• Possibly different for each particle.
• This promotes
• Good consistency in energy deposition
• less use of CPU in dense materials (compared to a
  common Energy)
• Yet appropriate length scales can vary greatly
  between different areas of a large detector
• Eg a vertex detector (5 mm) and a muon detector
  (2.5 cm).
• Having a unique (low) cut can create a
  performance penalty.
• New functionality,
• enabling the tuning of production thresholds at
  the level of a sub-detector.
• Created Region (or sub-detector)

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Cuts/Region Introduction

• A Cut here is a  production threshold 
• Only for physics processes that have infra-red
  divergence
• Not tracking cut (which does not exist in
  Geant4)
• GEANT4 up to now allows a unique cut in range
• One cut in range for each particle
• By default is the same cut for all particles
• Consistency of the physics simulated
• A volume with dense material will not dominate
  the simulation time at the expense of sensitive
  volumes with light material.
• Requests from ATLAS, BABAR, CMS, LHCb, , to
  allow several cuts
• Globally or per particle

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Motivation for several cuts

• Having a unique cut can be the source of
  performance penalties
• Part of the detector with lower cut needs fixes
  the cut for the all simulation
• Can be far too low than necessary in other parts
• Silicon vertex detector a few 10 mm
• Hadronic calorimeter 1 cm
• Other parts being geometrically far, too.

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Region example properties

• Introduce the concept of  region 
• Set of geometry volumes, typically of a
  sub-system
• Eg barrel end-caps of the calorimeter
• Or any group of volumes
• A cut in range is associated to a region
• a different range cut for each particle is
  allowed in a region .
• Typical Uses
• barrel end-caps of the calorimeter can be a
  region
• Deep areas of support structures can be a
  region.

Region B
Region B
Region B
Region C
c
Region B
Region A
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In Progress 2003 (highlights)

• Improvements of multiple scattering
• in straggling, backscattering
• Additional refinements of physics lists
• Continuous updates
• Design iteration of EM (std) processes
• With benefits in tailoring, maintenance
• Further extension and automation of testing
• Statistical testing benchmarks and test-beams

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In progress (also)

• The refinement of the design of EM physics
  processes through the use of models.
• To enable the specialization of key features
• To enable the easy use of different models for a
  single process (e.g. Ionization) in one
  application.
• Additional variance reduction techniques
• Filter for enhancing processes in hadronic
  interactions.
• Possible reorganization of G4RunManager
• For easier customization w.r.t. experiments
  framework

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Scheduled 2003 Releases

• Geant4 5.2
• End of June, 2003
• Geant4 6.0
• Middle of December, 2003
• Planned features
• http//wwwasd.web.cern.ch/wwwasd/geant4/source/pla
  nned_features.html

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User support

• New Achievements
• Technical Forum
• Liaison
• See next slides for details
• Tutorials
• DESY (end Sept, to be fixed)
• IEEE NSS/MIC _at_ Portland, OR (mid Oct, to be
  fixed)
• FNAL (Oct.27 Oct.29)
• HyperNews, mailing list, bug reporting system,
  daily private communications

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New Collaboration Agreement

• New Collaboration Agreement is at the very final
  draft stage.
• Expected to be agreed by whole collaboration and
  signing parties within this summer
• SLAC, CERN, IN2P3, INFN, KEK, ESA, PPARK, small
  universities, etc.
• with expectation of DESY (and FNAL?)
• New collaboration structure
• Facilitates new user support mechanisms

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New Geant4 Collaboration
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Technical Forum

• In the Technical Forum, the Geant4 Collaboration,
  its user community and resource providers,
  discuss
• major user and developer requirements, user and
  developer priorities, software implementation
  issues, prioritized plans, physics validation
  issues, user support issues
• The Technical Forum is open to all interested
  parties
• To be held at least 4 times per year at at least
  two locals
• The purpose of the forum is to
• Achieve, as much as possible, a mutual
  understanding of the needs and plans of users and
  developers.
• Provide the Geant4 Collaboration with the
  clearest possible understanding of the needs of
  its users.
• Promote the exchange of information about physics
  validation performed by Geant4 Collaborators and
  Geant4 users.
• Promote the exchange of information about user
  support provided by Geant4 Collaborators and
  Geant4 user communities.

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Liaison

• The Geant4 collaboration may appoint a Geant4
  member to act as Liaison for a user community. A
  Liaison interacts closely with the associated
  users to facilitate the communication with the
  Geant4 Collaboration.
• The collaboration acknowledges and encourages
  user communities and experiments to nominate a
  contact person. The Geant4 collaboration will
  make every effort to channel communication
  through him/her and provide a Geant4 liaison
  officer.
• This new achievement does not exclude any already
  existing communication channels.

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SLAC Geant4 team
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SLAC Geant4 team

• Covers most of the domains in Geant4
• Working with close contacts to BaBar, GLAST and
  NLC/NLD
• With other users mainly in US as well
• Keeping in touch with worlds major users

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Summary

• Results of comparing Geant4 versus data,
• Have are providing excellent yardsticks of EM
  performance
• Are testing the hadronics well, with increasing
  coverage
• Geant4 has demonstrated important strengths
• stability of results, flexibility, transparency.
• Geant4 is in production use today in running HEP
  experiments (BaBar, HARP)
• Geant4 is evolving
• With requirements from LHC experiments, BaBar and
  numerous other experiments and application
  domains.
• Refinements development are ongoing.
• Most recent release Geant4 version 5.1
  Patch-01 (May 19, 2003)
• Next scheduled release Geant4 version 5.2 (June
  27, 2003)
• User support will be more enhanced under the new
  Collaboration Agreement.
• SLAC Geant4 team is quite actively involving to
  most of the Geant4 domains and user supports.