geant4: an update
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Geant4: an update. An overview of Geant4’s recent developments. John Apostolakis, CERN Makoto Asai, SLAC for the Geant4 collaboration. Outline. Brief introduction to Geant4 Physics highlights Modeling validation New capabilities Detector description and collision detection - PowerPoint PPT PresentationTRANSCRIPT
Geant4: an update
John Apostolakis, CERNMakoto Asai, SLAC
for the Geant4 collaboration
An overview of Geant4’s recent developments
24th March 2003 2
Outline
1. Brief introduction to Geant42. Physics highlights
Modeling validation
3. New capabilities Detector description and collision
detection
4. Some current Developments In progress Planned for 2003
Introduction
ContextToolkit structure
Part 1
24th March 2003 4
GEANT 4 introduction Detector simulation tool-kit for HEP
offering alternatives, allowing for tailoringSoftware Engineering and OO technology
provide the method for building, maintaining it. Requirements from HEP & other domains:
LHC, heavy ions, CP violation, cosmic rays medical and space science applications
World-wide collaboration RD44 1994-1998 MoU 1999-today
24th March 2003 5
Geant4 Overview
Extensive & transparent physics models electromagnetic, hadronic, optical, decay, …
Powerful structure and kernel tracking, stacks, geometry, hits, …
Interfaces visualization, GUI, persistency.
Efficiency enhancing techniques Framework for fast simulation (shower
parameterization) Variance reduction / event biasing
Physics Highlights
Modelingand
Validation
Part 2
24th March 2003 7
Physics Development Highlights
Geant4 releases Dec 2001-today included New EM processes
And improvements to existing processes New theoretical hadronic models
In particular for the cascade energy range The release of ‘tailored’ physics lists
For different hadronics use cases. Numerous physics improvements
Including, for exampleCharge state for recoilsImproved X-sections for e-Nuclear, with hard
scattering
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Significant developments in EM (std) in 2002
Multiple scattering (L. Urban) Angular distributions (see next slides)
Ultra relativistic energies (H. Burkardt, S. Kelner, R. Kokoulin)
process Ionization for Generic Ions (V. Ivanchenko)
New model of Transition radiation (V. Grichine) for TR detectors
Redesign of few processes prototype model approach for Ionization and
Bremsstrahlung (V. Ivanchenko)
24th March 2003 9
Multiple scattering
Small differences between G4 & G3 observed below 1 MeV
- Results competitive versus data in G4 3.2
- Differences traced to Multiple Scattering
MS modeling improved in Geant4 4.0 & 5.0
Examples of comparisons to data
Thanks to L. Urban Angle (deg)
Geant4 4.0(Dec 2001)
15.7 MeV electrons on gold foil
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Multiple scattering
Angle (deg)
Refined modeling of angular distributions in Geant4
5.0
Modeling & comparisons:
L. Urban
Geant4 5.0 (Dec 2002)
24th March 2003 11
Hadronic physics: models, processes and ‘lists’
Illustrative example of assembling models into an inelastic process for set of particles Uses levels 1 & 2 of framework
CHIPS
QGSM Parame-terized
Ene
rgy
Element
particle
Pre-compoundmodel
Five level implementation frameworkVariety of models and cross-sections
for each energy regime, particle type, materialalternatives with different strengths and CPU requirements.
Components can be assembled in an optimized way for each use case.
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Models: Cascade energy range
Parameterized process (1997) Chiral Invariant Phase Space decay,“CHIPS”
For -Nucleus, capture, string-’backend’ First release Dec 2001 in Geant4 4.0 Refinements and extension in 2002
Bertini cascade (Dec 2002, Geant4 5.0) Re-engineered from HETC by HIP
See the presentation of A Heikinen Binary cascade model (Frankfurt, CERN)
First release for nucleon induced interactions (in G4 5.0) Extensive verification suite
See the presentation by D. Wright, V. Ivantchenko For further details,
see the next presentation (J.P. Wellisch)
M Kosov, P Degtyarenko,
JP Wellisch
A HeikinenN Stepanov
JPW
G Folger JPW
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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 HEP calorimetry. HEP 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 targetse.g. 400GeV protons on C or
Be medium energy production
targetse.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.html#wg.Had
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Physics lists for calorimetry LHEP is the fastest for CPU
uses the LEP and HEP parameterized models for inelastic scattering.
QGSP, uses theory-driven
modeling for reactions of s, Ks, and nucleons.
It employs Quark Gluon String Model
for the 'punch-through' interactions of the projectile
A Pre-equilibrium decay model
with an extensive evaporation phase to model the nucleus 'after the punch'.
QGSC, is similar but uses CHIPS for fragmentation The CHiral Invariant
Phase-Space decay (CHIPS)
FTFP replaces instead the string with a diffractive string
excitation similar to that in FRITJOF,
and the Lund fragmentation functions.
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Comparison projects Joint efforts for comparing Geant4 with
experiment & test-beam data. Results of EM comparisons: ‘peak’ between
2000-2002. Hadronic comparisons: 2002-ongoing.
Collaboration with experiments ATLAS (projects with data of numerous test
beams) BaBar (with data for tracker, drift chamber)
Many results have been presented at conferences & workshops, eg Calor 2002. And at regular LHC experiment-Geant4 physics
comparisons meetings
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LinearityMix and match
problem seen in parameterised models.
Problem disappears, as expected, when utilising theoretical models:Eg Quark-Gluon String
Model + CHIPS
For latest results please see the presentations of JP Wellisch & Atlas
Thanks to Atlas HEC and J.P. Wellisch
First results from April/May 2002
24th March 2003 19
Geant4 Hadronic Signals in ATLAS Calorimeters
Geant4 Hadronic Signals in ATLAS Calorimeters
Calorimeter pion Calorimeter pion response:response:
after discovery of “mix-and-match” problem (transition from low energy to high energy char-ged pion models) in the deposited energy from energy loss of charged particles in pion showers in the HEC (G4 4.0, early 2002): fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and QGS model tested;
e/π signal ration in HEC and TileCal still not well reproduced by Geant4 QGS or LHEP - but better than with GCalor in Geant3.21;
energy dependence in HEC in QGS smoother, “discontinuities” between ~20 GeV and ~80 GeV gone;
Calorimeter pion Calorimeter pion response:response:
after discovery of “mix-and-match” problem (transition from low energy to high energy char-ged pion models) in the deposited energy from energy loss of charged particles in pion showers in the HEC (G4 4.0, early 2002): fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and QGS model tested;
e/π signal ration in HEC and TileCal still not well reproduced by Geant4 QGS or LHEP - but better than with GCalor in Geant3.21;
energy dependence in HEC in QGS smoother, “discontinuities” between ~20 GeV and ~80 GeV gone;
HEC Pions
QGS
LHEPe/π
sig
nal ra
tio
e/π
sig
nal ra
tio
Pion energy [GeV]
Thanks to P. Loch, Atlas
As presented at Geant4 Workshop, 30th September 2002
Word highlights: JA, March 2003
New capabilities
Detector descriptionPerformanceVisualisation
Part 3
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Other Development highlights
Detector description New ways to create geometries Tools to detect incorrect geometry definitions A different field for any volume (or volume tree)
Overriding a global field
Ability to reduce initialisation time By saving/retrieving physics processes’ table
Variance reduction / event biasing Importance: biasing by geometry Leading particle biasing
24th March 2003 22
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 voxelizing some volumes
‘Illegal’ geometries detected & rejected E.g. incompatible daughters (placed & parameterized)
XML binding: GDML 1.0 released Specification & Implementation
• Refinements currently on ‘hold’.
G Cosmo
R Chytracek
I Hrivnacova G Cosmo
V Grichine
G Cosmo
Debugging geometriesDebugging 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 )• Created by S. Tanaka, released ca 1997
New commands to run verification tests• Created by DC Williams; released in 4.0
New example with full tracking / navigation• Created by M Liendl; released in 5.0
Thanks to S. Tanaka
24th March 2003 24
Variance reduction Geant4 had leading particle biasing option for “low energy” neutrons.
Now 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 released Further refinements & methods are under development.
Importance biasing: Splitting/Russian roulette (first released in G4 4.1, June 2002). Importance values can be associated to a volume
In the ‘mass’ geometry or in a dedicated ‘parallel’ geometry. Enabling simulation of shielding applications with improved time
efficiency by large factors Varied options in driving MC ‘history’ and scoring tallies No changes to the kernel were required, due to the flexibility of the
toolkit. Leading particle biasing
a-la MARS 95, for En<5GeV
M Dressel
N.Kanaya
24th March 2003 25
CPU Performance Our first 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 issues 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 Goal is that Geant4 is at least as fast as Geant3 in
almost all cases When its power is used.
24th March 2003 26
Geometry, hitsNew
“DTREE”: hierarchy display HEPREP driver for WIRED
Other Current Drivers OpenGL VRML DAWN Renderer Also from others, eg
IGUANA (for CMS simulation)
DAWN rendererThanks to S. Tanaka
Iguana, thanks to L.Tuura, I. Osborne
Visualization
Current development highlights
ImminentScheduled
Part 4
24th March 2003 28
In Progress 2003 (highlights)
Cuts per region See next slides
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
24th March 2003 29
Cuts in Geant4 (to date) Geant4 has had a unique production threshold
(‘cut’) expressed in length (range of secondary). For all volumes Possibly different for each particle.
This promotes Clear criteria for locality of energy deposition better use of CPU – less ‘wasted’ in dense materials
Yet appropriate length scales can vary greatly between different areas of a large detector Eg a vertex detector (5 m) and a muon detector (2.5 cm). Having a unique (low) cut can create a performance
penalty. So the part of the detector with the lowest cut need
fixed the cut for all the simulation.
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Motivation for several cuts
Having a unique cut enforced a choice between Sacrificing accuracy of energy deposition Accepting a performance penalty
Lifting the uniqueness of cuts Requested from LHC experiments & BaBar Implemented by introducing geometrical
‘regions’And enabling the choice of thresholds in a
region.
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Region & its 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
RegionB
Region A
Region B
Region B
Region C
c
24th March 2003 32
Cuts per region status
Design and implementation have been made without severe design revision of the existing
GEANT4; First implementation available in latest release
(Feb)
Comparable run-time performanceToday a penalty within 5% is seen, due to redundant
checks included for verification purposes
‘Full release’ will be in Geant4 5.1 (end April) With further refinements, tests, validation.
24th March 2003 33
MS in progress
Multiple scattering:
Refinements
Backscattering
Straggling
Transmitted energy
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MS: straggling
Lateral stragglingof 2.5 MeV protonsAfter mylar foils
Fit to data
Geant4 5.1 (April 2003)
24th March 2003 36
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.
24th March 2003 37
Some further 2003 development highlightsAdditions to physics processes/models
induced binary cascade model, .. EM-std implementation with “model” approach. Refinements, including
Improvement to recoil in elastic scattering Improved X-sections for pions.
Revisions of the ‘tailored’ physics lists Incorporating results of validation
Variance reduction Physics process enhancement Leading particle biasing Plus refinements to importance biasing
24th March 2003 38
Review and Releases Review October 2002
Report available at http://cern.ch/geant4 Developments available in releases
Every two months Latest release (February)
Included cuts per region Upcoming releases
Next minor release is Geant4 5.1 planned for end-April Incorporating cut per region, developments in progress. Release timeframe selected to aid in CMS production.
‘Scheduled’ release Geant4 5.2 for end-June Further refinements, developments
2003 work items & planned release contents to be available soon
Started from User & Experiment Requirements and Requests Next major release Geant4 6.0 is scheduled for December 2003.
24th March 2003 39
SummaryResults of comparing Geant4 versus data,
Have & are providing excellent ‘yardsticks’ of EM perf. Are testing the hadronics well, with increasing
coverageGeant4 has demonstrated important strengths:
stability of results, flexibility, transparency. it is in production use today in running HEP
experiments (BaBar, HARP)Geant4 is evolving
With the feedback from LHC exper., BaBar and numerous other experiments and application domains.
Refinements & development are ongoing.
http://cern.ch/geant4/
THE END
Thanks to allContributorsUsers
After the END …
Slides after this are backups, not part of the presentation.
v0.8 24th March 2003, 18:40 GMT
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Electromagnetic physics
Gammas: Gamma-conversion, Compton scattering, Photo-electric effect
Leptons(e, ), charged hadrons, ions Energy loss (Ionisation, Bremstrahlung) or PAI model energy loss,
Multiple scattering, Transition radiation, Synchrotron radiation,
Photons: Cerenkov, Rayleigh, Reflection, Refraction, Absorption,
Scintillation
High energy Alternative implementation
‘Standard’ for applications that do not need to go below 1 KeV ‘Low Energy’: down to 250eV (e+/), O(0.1) m for hadrons
Including specialized HEP applications
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Shower profile
1 GeV electron in H2O
G4, DataG3
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Support: new & continued
Documentation Revisions of the user and reference guides
After assessments of overall structure & detailed LXR for code reference
see http://geant4www.triumf.ca/lxr/New tool for collecting requirements
Continued Support of users’ questions, problems
HyperNews, Problem reporting system, email. of comparisons with data
By wide variety of users, in HEP, space, medical phys., ..
24th March 2003 46
Testing and QA 2002/3
Establishment of ‘statistical testing’ suite Automated comparison of physics
quantities Against ‘standard’ data (eg NIST)In ‘test-beam’ applicationsIncluding ‘regression testing’.For details see
Establishing a benchmark suite for computing performance.
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Examples of improvements
Fixes and improvements in Geant4 release 4.1 (June 2002)
Geometry Fix for voxelisation of reflected volumes Fix for exit normal angle Fix for problem in very small step in field
EM Improvements in Multiple Scattering, Ionisation, ..
Hadronics Fix for energy conservation in parametrised
models. Fix for small peak at =0 in parametrised models.
24th March 2003 48
BaBar
Geant4 based simulation since 2001 production.
More than 109 events (through Oct 2002)
Used Geant4 3.1+fixes, own transport.
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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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Geant4 Collaboration
Collaborators also from non-member institutions, including
Budker Inst. of PhysicsIHEP Protvino
MEPHI Moscow
Lebedev