Geant4: an update John Apostolakis, CERN Makoto Asai, SLAC for the Geant4 collaboration An overview of Geant4’s recent developments.

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

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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

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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

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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)

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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)

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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

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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

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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 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

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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

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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.

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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

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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)

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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.

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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

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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.

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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.

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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