Dr. Guy Tel-Zur

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Computational Physics An Introduction to the Geant4 toolkit

An Introduction to the Geant4 toolkit

Many of the slides are from a presentation by: J. Apostolakis, CERN

for the Geant4 collaboration

Geant4

Home page: http://geant4.cern.ch/Important paper:

Geant4 – a simulation toolkitTutorial:

http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=58317

Live CD: https://twiki.cern.ch/twiki/bin/view/Geant4/Geant4CernVM 3

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Overview

Simulation packages/toolkits Key capabilities and concepts

What it can do - highlightsApplication areas

What is inside – lightning tourBrief highlights of capabilities

Transparency of results Open source

GEANT4: the collaboration

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What can a simulation package or toolkit do ?A Package provides ‘general’ tools to

undertake (some or all) of the key tasks: tracking, and geometrical propagation modelling of physics interactions, visualization, persistency

and enable you to describe your setup’s detector geometry, radiation source, details of sensitive regions

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GEANT 4

Detector simulation tool-kit from HEP full functionality: geometry, tracking, physics,

I/O offers alternatives, allows for tailoring

Software Engineering and OO technology provide the architecture & methods for

maintaining itRequirements from:

current and future HEP experiments medical and space science applications

World-wide collaboration

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Key Capabilities ‘Kernel’: create, manage, move tracks

tracking, stacks, geometry, hits, …Extensible, flexible

Physics Processes X-section, final-state models for electromagnetic, hadronic, …

Can be ‘assembled’ for use in an application area Tools for faster simulation

‘Cuts’, framework shower parameterisation Event biasing, variance reduction.

Open interfaces for input/output User commands, visualization, persistency

Brief History

Geant4 started as RD44 project (1994-98) Amongst first OO in HEP, 1st for

simulation Dec 1998: 1st supported release

Geant4.0.0First uses in production in several

fields Space: 1999 XMM (X-ray telescope) HEP: 2001 BaBar, 2004

ATLAS/CMS/LHCbRegular public releases (1-2 per

year) Geant4 release 9.0 (Jun 07), 9.3 (Dec

09) Guy: Dec. 17, 2010: new release:

9.4

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APPLICATION AREAS

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HIGH ENERGY PHYSICS

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BaBar

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Now simulating PEP beam line as well (-9m < zIP < 9m)

Courtesy of D.Wright (SLAC)

BaBar at SLAC was the pioneer experiment in HEP in use of Geant4 Started in 2000

Simulated several x 1010 events

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Pion longitudinal shower profile in stand-alone

ATLAS TileCal test-beam at 90o

Data

For Protons : -(20%-40%) at 10 λ.

MC within ~ ±10% up to 10 λ.

Thanks to Atlas Tilecal

14Courtesy: CMSTalk of S. Banerjee, Geant4 Workshop 2009

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Boulby Mine dark matter search Prototype Simulation

Courtesy of H. Araujo, A. Howard, IC London

LXe

GXe

PMT

mirror

source

One High Energy event

17Courtesy of V.D.Elvira (FNAL)

Geant4 for beam transportation

AEROSPACE

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g astrophysics

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g-ray bursts

AGILE GLAST

Typical telescope: Tracker Calorimeter Anticoincidence

g conversion electron interactions multiple scattering d-ray production charged particle tracking

GLAST

GLAST

Bepi Colombo: X-Ray Mineralogical Survey of Mercury

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Alfonso Mantero, Thesis, Univ. Genova, 2002

Space Environments and Effects Section

BepiColomboESA cornerstone mission to Mercury

Courtesy of ESA Astrophysics

PlanetoCosmicsGeant4 simulation of Cosmic Rays in planetary Atmo-/Magneto- spheres

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MEDICAL PHYSICS

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http://top25.sciencedirect.com/index.php?subject_area_id=21

A QUICK WALK THROUGH GEANT4

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Key Domains of the Simulation

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Top Level Category Diagram (part 1)

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Top Level Category Diagram (part 2)

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Describes a Setup

Hierarchy of volumes Many volumes

repeat Volume & sub-tree

Up to hundreds of thousands of volumes

Importing solids from CAD systems

Navigates in Detector

Locates a point Computes a step

Linear intersection

Geometry: what it does

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Electromagnetic physics

Gammas: Gamma-conversion, Compton scattering, Photo-electric

effect

Leptons(e, m), charged hadrons, ions Energy loss (Ionisation, Bremstrahlung), Multiple scattering,

Transition radiation, Synchrotron radiation, e+ annihilation.

Photons: Cerenkov, Rayleigh, Reflection, Refraction, Absorption,

Scintillation High energy muons

A choice of implementations for most processes “Standard”: performant when relevant physics above 1 KeV “Low Energy”: Extra accuracy for application delving below

1 KeV

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Hadronic processes

Hadronic physics is included in Geant4 a powerful and flexible framework and implementations of physics X-sections &

models.A variety of models and cross-sections

for each energy regime, particle type, material alternatives with different strengths and

computing resource requirementsComponents can be assembled in an

optimised way for each use case.

Openness and Extensibility

As a toolkit with open-source code, Geant4 can be extended in many ways Expected/simple

Creating a new shape (G4VSolid) Unusual, but predicted

New processes, for physics or user action Radical extensions

Reversing time (two ways) Creating ‘on-the-fly’ density for a material

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Practical considerations Starting off: what you need

Compatible platform Need CLHEP foundation class library One or more visualisation libraries (possibly from

system, e.g. OpenGL)

CLHEP is used for key common classes ThreeVector (G4ThreeVector is a name for

CLHEP::HepThreeVector) FourVector Random Number Generators, ..

Coding is needed – except if someone did it for you. Modify existing C++ ‘code’ to describe your setup Create you own class to describe eg a magnetic field.

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Platforms

What works ‘best’ (used by developers, main testing) Scientific Linux 4 or 5 and gcc 4.3 (HEP production) MacOS 10.5 Leopard

What we also support (tested + numerous users) Windows (XP) & Visual C++

numerous users

What we expect to work Other Linux flavours with gcc 4.1 and 4.3

Possibly with fewer options, eg missing some visualisation

What others ‘ported’ and check Sun Solaris

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GEANT4 COLLABORATION

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Geant4 Collaboration

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Collaborators also from non-member institutions, including

IHEPMEPHI Moscow

Jefferson Laboratory

Lebedev

TRIUMF

UK STFCLIP

The Toolkit Examples

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Three levels:

Hands on!

• Time to get your hands on Geant4– Copy exercises– Your first run of a simple example

• To start, please look at

http://www.ifh.de/geant4/g4course2010

Else, if you have difficulty to reach that use

http://www-zeuthen.desy.de/geant4/g4course2010

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User: geant, pw: geant2010IP = 192.168.11.128

Example N02This example simulates a simplified fixed target experiment.

1- GEOMETRY DEFINITION

The setup consists of a target followed by six chambers of increasing

transverse size. These chambers are located in a region called Tracker

region. Their shape are boxes, constructed as parametrised volumes

(ChamberParametrisation class).

The default geometry is constructed in DetectorConstruction class.

One can change the material of the target and of the chambers

interactively via the commands defined in the DetectorMessenger class.

In addition a transverse uniform magnetic field can be applied (see

N02MagneticField and DetectorMessenger classes).

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2- PHYSICS LIST

The particle's type and the physic processes which will be available in this example are set in PhysicsList class.

In this example, all the so called 'electromagnetic processes' are introduced for gamma, charged leptons, and charged hadrons (see the method PhysicsList::ConstructEM()).

An important data member of this class is the defaultCutValue which defines the production threshold of secondary particles (only Ionisation and Bremsstrahlung processes are concerned by this CutValue). Notice that the CutValue must be given in unit of length, corresponding to the stopping range of the particle. It is automatically converted in energy for each material, and a table is printed in the method PhysicsList::SetCuts()

In addition the build-in interactive command: /process/(in)activate processName allows to activate/inactivate the processes one by one.

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3- RUNS and EVENTS

The primary kinematic consists of a single particle which hits the target perpendicular to the input face. The type of the particle and its energy are set in the PrimaryGeneratorAction class, and can be changed via the G4 build-in commands of ParticleGun class.

A RUN is a set of events.

The user has control: -at Begin and End of each run (class RunAction) -at Begin and End of each event (class EventAction) -at Begin and End of each track (class TrackingAction, not used here) -at End of each step (class SteppingAction)

The class SteppingVerbose prints some informations step per step, under the control of the command: /tracking/verbose 1 It inherits from G4SteppingVerbose, and has been setup here in order to illustrate how to extract informations from the G4 kernel during the tracking of a particle.

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4- USER' LIMITS

We illustrate how to introduce tracking constraints like maximum step length, minimum kinetic energy ..etc.., via G4UserLimits class. See DetectorConstruction and PhysicsList.

5- DETECTOR RESPONSE

A HIT is a record, track per track (even step per step), of all the informations needed to simulate and analyse the detector response.

In this example the Tracker chambers are considered as the detector. Therefore the chambers are declared 'sensitive detectors' (SD) in the DetectorConstruction class.

Then, a Hit is defined as a set of 4 informations per step, inside the chambers, namely: - the track identifier (an integer), - the chamber number, - the total energy deposit in this step, - the position of the deposit.

A given hit is an instance of the class TrackerHit which is created during the tracking of a particle, step by step, in the method TrackerSD::ProcessHits(). This hit is inserted in a HitsCollection. The HitsCollection is printed at the end of event (via the method TrackerSD::EndOfEvent()), under the control of the command: /hits/verbose 1

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6- VISUALIZATION

The Visualization Manager is set in the main(). The initialisation of the drawing is done via a set of /vis/ commands in the macro vis.mac. This macro is automatically read from the main when running in interactive mode.

The tracks are automatically drawn at the end of event and erased at the beginning of the next run.

The visualization (with OpenGL driver) assumes two things: 1- the visualisation & interfaces categories have been compiled with the environment variable G4VIS_BUILD_OPENGLX_DRIVER. 2- exampleN02.cc has been compiled with G4VIS_USE_OPENGLX.

(The same with DAWNFILE instead of OPENGLX)

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7- USER INTERFACES

The default command interface, called G4UIterminal, is done via standart cin/G4cout. On Linux and Sun-cc on can use a smarter command interface G4UItcsh. It is enough to set the environment variable G4UI_USE_TCSH before compiling exampleN02.cc

8- HOW TO START ?

- compile and link to generate an executable % cd N02 % gmake

- execute N02 in 'batch' mode from macro files (without visualization) % exampleN02 run1.mac

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- execute N02 in 'interactive mode' with visualization % exampleN02 .... Idle> type your commands. For instance: Idle> /run/beamOn 10 .... Idle> /control/execute run2.mac .... Idle> exit

Show in editor printout of exampleN02, see file: ./geant/exampleN02_printout.txt

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The END

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Resources for more information Geant4 web site

http://cern.ch/geant4/ Geant4 Training Page

http://cern.ch/geant4/support/ and follow “Training” link,

Geant4 training INFN / EM ‘Low-energy’

http://www.ge.infn.it/geant4/training/

Geant4 Workshops and Users Workshops presentations Latest at the home page,

previous at http://geant4.web.cern.ch/geant4/collaboration/meetings_minutes.html#G4workshops

Geant4 Physics WG web sites Which can all be found at

http://cern.ch/geant4/organisation/working_groups.html

Geant4 Low-Energy Electromagnetic WG web site

http://www.ge.infn.it/geant4/lowE/

Geant4 EM (standard) see below

Geant4 Hadronic WG home Papers on G4 and its

validation “Geant4: a simulation

toolkit”, Nucl Instr and Methods A 506 (2003), 250-303

“Validation of GEANT4, an object-oriented MC toolkit for simulations in medical physics” J.F. Carrier et al, Med Phys 32 (2004), p 484.

Note: “Training” page is also directly accessed at http://cern.ch/geant4/milestones/training/training-milestone.html

ElectroMagnetic (standard) WG home page is at http://cern.ch/geant4/working_groups/electromagnetic/electromagneticWG.html

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Geant4 Capabilities & Use

• Kernel: create geometry, hits, …• Physics Processes

– models for EM, hadronics, …– ‘assembled’ into physics lists for application area

• Tools for faster simulation– Shower parameterisation & Event biasing.

• Open interfaces for input/output– User commands, visualization

• Verification and validation for use cases• Using it

– via ready applications (eg GATE)– by starting with examples & customising

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Acknowledgements

Thanks to those who have contributed-to creating slides for tutorials / talk, that I borrowed

Thanks to all those who have contributed -to the development of Geant4, -to its validation for these and other application areas,

-to those who have applied it -particularly those who have given feedback.

Note that it is a large task to give credit to all of them individually.