Geant4: an update

John Apostolakis, CERNMakoto Asai, SLAC

for the Geant4 collaboration

Version 0.5.4 23rd March 2003, 16:30

24th March 2003 2

Outline

Brief introduction to Geant4Physics highlights

Modeling validation

New capabilities Detector description and collision

detectionSome of the Developments

In progress Planned for 2003

24th March 2003 3

GEANT 4

Detector simulation tool-kit for HEP offering alternatives, allowing for tailoring

Software Engineering and OO technology provide the method for building, maintaining

it. Requirements from:

LHC heavy ions, CP violation, cosmic rays medical and space science applications

World-wide collaboration

24th March 2003 4

Geant4 Capabilities

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

24th March 2003 5

Physics Development Highlights

Geant4 releases Dec 2001-today included New theoretical hadronic models

CHIPS for -Nucleus, capture, ..Cascade models: Bertini (HETC) and Binary

New EM processes to pair new TR models

Numerous physics improvementsIncluding, for exampleCharge state for recoilsImproved X-sections for e-Nuclear, with hard

scattering

24th March 2003 8

Multiple scattering

Examples of comparisons: 15.7 MeV e-

on gold foil

(figure this page)

Modelling & comparisons:

L. UrbanAngle (deg)

24th March 2003 9

Multiple scattering

Angle (deg)

Examples of comparisons: 15.7 MeV e-

on gold foil

Modelling & comparisons:

L. Urban

24th March 2003 10

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)

24th March 2003 11

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.

24th March 2003 12

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.

Z

24th March 2003 13

Models: Cascade energy range

Parameterized process (1997)Chiral Invariant Phase Space decay,“CHIPS”

Development 2000-2001 (M Kosov, P Degtyarenko, JP Wellisch) Refinements and extension in 2002

Bertini cascade (Dec 2002, Geant4 5.0) Re-engineered from HETC,

See the presentation of A Heikinen

Binary cascade model (Frankfurt, CERN) First release for nucleon induced interactions (in Geant4

5.0) Extensive verification suite

See the presentation by D. Wright For other details,

see the next presentation (J.P. Wellisch)

24th March 2003 14

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

24th March 2003 15

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 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

24th March 2003 17

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).

Thanks to Atlas HEC and J.P. Wellisch

Status of May 2002

24th March 2003 18

BaBar

Geant4 based simulation since 2001 production.

More than 109 events (through Oct 2002)

Used Geant4 3.1+fixes, own transport.

24th March 2003 20

Other Development highlights

Various improvements Ability to reduce initialisation time

By saving/retrieving physics processes’ table A different field for any volume (or volume tree)

Overriding a potential global ‘default’ field Additional ways to create geometries Detect and debug incorrect geometry definitions

Variance reduction Importance: biasing by geometry

In real or ’ghost’ geometry• Eg enabling simulation of shielding applications with

improved time efficiency by large factors Leading particle biasing

• a-la MARS 95, for En<5GeV

24th March 2003 21

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’.

G Cosmo

R Chytracek

I Hrivnacova G Cosmo

V Grichine

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• 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 / navigationUses the full hierarchy & the Navigator

• Created by M Liendl; released in 5.0 Thanks to S. Tanaka

24th March 2003 23

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

24th March 2003 24

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 Goal is that Geant4 is at least as fast as Geant3 in

almost all cases When its power is used.

24th March 2003 25

Geometry, hitsNew

“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)

DAWN rendererThanks to S. Tanaka

Iguana, thanks to L.Tuura, I. Osborne

Visualization

24th March 2003 26

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 27

Cuts per region (precis) 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) 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)

24th March 2003 28

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;

24th March 2003 29

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;Hadronic calorimeter: 1 cm;

Other parts being geometrically far, to.

24th March 2003 31

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

RegionB

Region A

Region B

Region B

Region C

c

24th March 2003 33

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 34

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 35

Scheduled 2003 Development: highlights

Cuts per region Additional physics processes/models

Hadronic: induced binary cascade model, .. EM: refinements to multiple scattering; “models”.

Refinements, including Improvement to recoil in elastic scattering Improved X-sections for pions.

Variance reduction Physics process enhancement Refinements to importance biasing. Leading particle

24th March 2003 36

Geant4 Collaboration

Collaborators also from non-member institutions, including

Budker Inst. of PhysicsIHEP Protvino

MEPHI Moscow

Lebedev

24th March 2003 37

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

Planned: Geant4 5.1 release end-April Geant4 5.2 scheduled for end-June Release timeframe(s) adjusted for customer needs

Workplan User & Experiment Requirements and Requests Next major release Geant4 6.0 scheduled for December.

24th March 2003 38

SummaryResults of comparing Geant4 versus data,

Have & are providing excellent ‘yardsticks’ of EM perf. 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 exper., BaBar and

numerous other experiments and application domains.Refinements & development are ongoing.

http://cern.ch/geant4/

THE END

Slides after this are backup slides, deleted from the presentation

24th March 2003 40

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 41

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.

24th March 2003 42

Geant4 Capabilities

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

24th March 2003 43

Summary

Geant4 is in production use today in running HEP experiments (BaBar, HARP)

Results of comparing Geant4 versus data are growing month by month, have provided important ‘yardsticks’.

Geant4 has demonstrated important strengths: stability of results, flexibility, transparency.

Refinements & development are ongoing.

24th March 2003 44

Testing tools

Improvements of tools for automation of testing, followup Tinderbox Bonsai LXR for use in testing followup

24th March 2003 45

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.