1. Geant4: an update Makoto Asai, SLAC On behalf of
the Geant4 collaboration
and the SLAC Geant4 team
21 May 2003
LCSim SLAC

2. Outline Most recent release Physics highlights New capabilities
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
May 21st, 2003

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
May 21st, 2003

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

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)
May 21st, 2003

6. Comparison projects
Joint efforts for comparing Geant4 with experiment & test-beam data.
Results of EM comparisons:
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.
May 21st, 2003

7. 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
May 21st, 2003

8. 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 GeV p on light targets
LHC neutron fluxes
Air shower applications
low background experiments
Contributors:
working_groups.html#wg.Had
May 21st, 2003

9. 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).
These comparisons are from May Updated comparisons will be presented by ATLAS collaborators. Additional plots regarding the latest update of pion cross sections is expected in JP Wellisch’s presentation.
Status of May 2002
May 21st, 2003
Thanks to Atlas HEC and J.P. Wellisch

10. BaBar Geant4 based simulation since 2001 production.
More than 109 events (through Oct 2002)
Used Geant4 3.1+fixes, own transport.
May 21st, 2003

11. 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
May 21st, 2003

12. 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

13. Variance reduction Importance biasing:
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
May 21st, 2003

14. 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.
Geometry performance goals
Wider choice of geometry descriptions that obtain optimal or near-optimal performance
Utilising the simplest approach of placing lots of ‘placements’ volumes should provide acceptable performance in most cases.
May 21st, 2003

15. Visualization Geometry, hits New Other Current Drivers
DAWN renderer
Thanks to S. Tanaka
Visualization
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)
May 21st, 2003
Iguana, thanks to L.Tuura, I. Osborne

16. 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)
May 21st, 2003

17. 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;
May 21st, 2003

18. 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.
May 21st, 2003

19. 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
Some Details:
A region
- Has one or several ‘root’ volumes
The world is in a predefined ‘default region’
Region B
Region A
May 21st, 2003

20. 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

21. 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

22. Scheduled 2003 Releases Geant4 5.2 Geant4 6.0 Planned features
End of June, 2003
Geant4 6.0
Middle of December, 2003
Planned features
May 21st, 2003

23. User support New Achievements Tutorials
Technical Forum
Liaison
See next slides for details
Tutorials
DESY (end Sept, to be fixed)
IEEE Portland, OR (mid Oct, to be fixed)
FNAL (Oct.27 – Oct.29)
HyperNews, mailing list, bug reporting system, daily “private” communications
May 21st, 2003

24. 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

25. New Geant4 Collaboration
May 21st, 2003

26. 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.
May 21st, 2003

27. 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.
May 21st, 2003

28. SLAC Geant4 team
May 21st, 2003

29. 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

30. 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 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.
May 21st, 2003