Geant4: an update

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

21 May 2003 LCSim workshop @ SLAC

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

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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 May 21st, 2003 3

Multiple scattering

 Examples of comparisons:  15.7 MeV e on gold foil Modelling & comparisons: L. Urban May 21st, 2003 Angle (deg) 4

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) May 21st, 2003 5

Comparison projects

 Joint efforts for comparing test-beam data . Geant4 with   Results of EM comparisons: 2000-2002.

Hadronic comparisons: 2002-ongoing.

experiment &   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 4 th 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 May 21st, 2003 7

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 applications with 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/ May 21st, 2003 working_groups.html#wg.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).

May 21st, 2003 Status of May 2002 Thanks to Atlas HEC and J.P. Wellisch 9

May 21st, 2003

BaBar

Geant4 based simulation since 2001 production.

More than 10 9 events (through Oct 2002) Used Geant4 3.1+fixes, own transport.

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Improvements in Geometry

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

R Chytracek May 21st, 2003 11

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Debugging geometries

It is easy to create  overlaps 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’ is now addressed by    DAVID  that intersects volumes directly Uses graphical representations  By S. Tanaka, released circa 1997 New built-in run-time verification tests by its own navigation   commands Using solids and a grid of rays Created DC Williams; released in 4.0

to run New example  with full tracking / navigation Uses the full hierarchy & the Navigator  Created by M Liendl; released in 5.0 Thanks to S. Tanaka

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:   M Dressel 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.

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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

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High quality Postscript

Also from others, eg  IGUANA (for CMS simulation) May 21st, 2003 Iguana, thanks to L.Tuura, I. Osborne 15

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 m m) 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) May 21st, 2003 16

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) G EANT 4 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 A TLAS , B ABAR , C MS , L HCb , …, to allow several cuts;  Globally or per particle; May 21st, 2003 17

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 m m;  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 c B Region A Region B Region C Region B Region B May 21st, 2003 19

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 May 21st, 2003 20

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. experiment’s framework May 21st, 2003 21

Scheduled 2003 Releases

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Geant4 5.2

 End of June, 2003

Geant4 6.0

 Middle of December, 2003

Planned features

 http://wwwasd.web.cern.ch/wwwasd/geant4/ source/planned_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 @ Portland, OR (mid Oct, to be fixed)  FNAL (Oct.27 – Oct.29) HyperNews , mailing list, bug reporting system, daily “private” communications May 21st, 2003 23

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 May 21st, 2003 24

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 world’s major users May 21st, 2003 29

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.

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